{-# LANGUAGE FlexibleContexts    #-}
{-# LANGUAGE LambdaCase          #-}
{-# LANGUAGE MultiWayIf          #-}
{-# LANGUAGE NamedFieldPuns      #-}
{-# LANGUAGE ParallelListComp    #-}
{-# LANGUAGE ScopedTypeVariables #-}

{-# OPTIONS_GHC -Wno-incomplete-uni-patterns   #-}

module GHC.Tc.Errors(
       reportUnsolved, reportAllUnsolved, warnAllUnsolved,
       warnDefaulting,

       -- * GHC API helper functions
       solverReportMsg_ExpectedActuals, mismatchMsg_ExpectedActuals
  ) where

import GHC.Prelude

import GHC.Driver.Env (hsc_units)
import GHC.Driver.DynFlags
import GHC.Driver.Ppr
import GHC.Driver.Config.Diagnostic

import GHC.Rename.Unbound

import GHC.Tc.Types
import GHC.Tc.Utils.Monad
import GHC.Tc.Errors.Types
import GHC.Tc.Errors.Ppr
import GHC.Tc.Types.Constraint
import GHC.Tc.Utils.TcMType
import GHC.Tc.Zonk.Type
import GHC.Tc.Utils.TcType
import GHC.Tc.Zonk.TcType
import GHC.Tc.Types.Origin
import GHC.Tc.Types.Evidence
import GHC.Tc.Types.EvTerm
import GHC.Tc.Instance.Family
import GHC.Tc.Utils.Instantiate
import {-# SOURCE #-} GHC.Tc.Errors.Hole ( findValidHoleFits, getHoleFitDispConfig, pprHoleFit )

import GHC.Types.Name
import GHC.Types.Name.Reader
import GHC.Types.Id
import GHC.Types.Var
import GHC.Types.Var.Set
import GHC.Types.Var.Env
import GHC.Types.Name.Env
import GHC.Types.SrcLoc
import GHC.Types.Basic
import GHC.Types.Error
import qualified GHC.Types.Unique.Map as UM

--import GHC.Rename.Unbound ( unknownNameSuggestions, WhatLooking(..) )
import GHC.Unit.Module
import qualified GHC.LanguageExtensions as LangExt

import GHC.Core.Predicate
import GHC.Core.Type
import GHC.Core.Coercion
import GHC.Core.TyCo.Ppr     ( pprTyVars )
import GHC.Core.InstEnv
import GHC.Core.TyCon
import GHC.Core.DataCon

import GHC.Utils.Error  (diagReasonSeverity,  pprLocMsgEnvelope )
import GHC.Utils.Misc
import GHC.Utils.Outputable as O
import GHC.Utils.Panic
import GHC.Utils.FV ( fvVarList, unionFV )

import GHC.Data.Bag
import GHC.Data.List.SetOps ( equivClasses, nubOrdBy )
import GHC.Data.Maybe
import qualified GHC.Data.Strict as Strict

import Control.Monad      ( unless, when, foldM, forM_ )
import Data.Foldable      ( toList )
import Data.Function      ( on )
import Data.List          ( partition, sort, sortBy )
import Data.List.NonEmpty ( NonEmpty(..), nonEmpty )
import qualified Data.List.NonEmpty as NE
import Data.Ord         ( comparing )
import qualified Data.Semigroup as S

{-
************************************************************************
*                                                                      *
\section{Errors and contexts}
*                                                                      *
************************************************************************

ToDo: for these error messages, should we note the location as coming
from the insts, or just whatever seems to be around in the monad just
now?

Note [Deferring coercion errors to runtime]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
While developing, sometimes it is desirable to allow compilation to succeed even
if there are type errors in the code. Consider the following case:

  module Main where

  a :: Int
  a = 'a'

  main = print "b"

Even though `a` is ill-typed, it is not used in the end, so if all that we're
interested in is `main` it is handy to be able to ignore the problems in `a`.

Since we treat type equalities as evidence, this is relatively simple. Whenever
we run into a type mismatch in GHC.Tc.Utils.Unify, we normally just emit an error. But it
is always safe to defer the mismatch to the main constraint solver. If we do
that, `a` will get transformed into

  co :: Int ~ Char
  co = ...

  a :: Int
  a = 'a' `cast` co

The constraint solver would realize that `co` is an insoluble constraint, and
emit an error with `reportUnsolved`. But we can also replace the right-hand side
of `co` with `error "Deferred type error: Int ~ Char"`. This allows the program
to compile, and it will run fine unless we evaluate `a`. This is what
`deferErrorsToRuntime` does.

It does this by keeping track of which errors correspond to which coercion
in GHC.Tc.Errors. GHC.Tc.Errors.reportTidyWanteds does not print the errors
and does not fail if -fdefer-type-errors is on, so that we can continue
compilation. The errors are turned into warnings in `reportUnsolved`.
-}

-- | Report unsolved goals as errors or warnings. We may also turn some into
-- deferred run-time errors if `-fdefer-type-errors` is on.
reportUnsolved :: WantedConstraints -> TcM (Bag EvBind)
reportUnsolved :: WantedConstraints -> TcM (Bag EvBind)
reportUnsolved WantedConstraints
wanted
  = do { binds_var <- TcM EvBindsVar
newTcEvBinds
       ; defer_errors <- goptM Opt_DeferTypeErrors
       ; let type_errors | Bool -> Bool
not Bool
defer_errors = DiagnosticReason
ErrorWithoutFlag
                         | Bool
otherwise        = WarningFlag -> DiagnosticReason
WarningWithFlag WarningFlag
Opt_WarnDeferredTypeErrors

       ; defer_holes <- goptM Opt_DeferTypedHoles
       ; let expr_holes | Bool -> Bool
not Bool
defer_holes = DiagnosticReason
ErrorWithoutFlag
                        | Bool
otherwise       = WarningFlag -> DiagnosticReason
WarningWithFlag WarningFlag
Opt_WarnTypedHoles

       ; partial_sigs      <- xoptM LangExt.PartialTypeSignatures
       ; let type_holes | Bool -> Bool
not Bool
partial_sigs
                        = DiagnosticReason
ErrorWithoutFlag
                        | Bool
otherwise
                        = WarningFlag -> DiagnosticReason
WarningWithFlag WarningFlag
Opt_WarnPartialTypeSignatures

       ; defer_out_of_scope <- goptM Opt_DeferOutOfScopeVariables
       ; let out_of_scope_holes | Bool -> Bool
not Bool
defer_out_of_scope
                                = DiagnosticReason
ErrorWithoutFlag
                                | Bool
otherwise
                                = WarningFlag -> DiagnosticReason
WarningWithFlag WarningFlag
Opt_WarnDeferredOutOfScopeVariables

       ; report_unsolved type_errors expr_holes
                         type_holes out_of_scope_holes
                         binds_var wanted

       ; ev_binds <- getTcEvBindsMap binds_var
       ; return (evBindMapBinds ev_binds)}

-- | Report *all* unsolved goals as errors, even if -fdefer-type-errors is on
-- However, do not make any evidence bindings, because we don't
-- have any convenient place to put them.
-- NB: Type-level holes are OK, because there are no bindings.
-- See Note [Deferring coercion errors to runtime]
-- Used by solveEqualities for kind equalities
--      (see Note [Failure in local type signatures] in GHC.Tc.Solver)
reportAllUnsolved :: WantedConstraints -> TcM ()
reportAllUnsolved :: WantedConstraints -> TcM ()
reportAllUnsolved WantedConstraints
wanted
  = do { ev_binds <- TcM EvBindsVar
newNoTcEvBinds

       ; partial_sigs      <- xoptM LangExt.PartialTypeSignatures
       ; let type_holes | Bool -> Bool
not Bool
partial_sigs  = DiagnosticReason
ErrorWithoutFlag
                        | Bool
otherwise         = WarningFlag -> DiagnosticReason
WarningWithFlag WarningFlag
Opt_WarnPartialTypeSignatures

       ; report_unsolved ErrorWithoutFlag
                         ErrorWithoutFlag type_holes ErrorWithoutFlag
                         ev_binds wanted }

-- | Report all unsolved goals as warnings (but without deferring any errors to
-- run-time). See Note [Safe Haskell Overlapping Instances Implementation] in
-- "GHC.Tc.Solver"
warnAllUnsolved :: WantedConstraints -> TcM ()
warnAllUnsolved :: WantedConstraints -> TcM ()
warnAllUnsolved WantedConstraints
wanted
  = do { ev_binds <- TcM EvBindsVar
newTcEvBinds
       ; report_unsolved WarningWithoutFlag
                         WarningWithoutFlag
                         WarningWithoutFlag
                         WarningWithoutFlag
                         ev_binds wanted }

-- | Report unsolved goals as errors or warnings.
report_unsolved :: DiagnosticReason -- Deferred type errors
                -> DiagnosticReason -- Expression holes
                -> DiagnosticReason -- Type holes
                -> DiagnosticReason -- Out of scope holes
                -> EvBindsVar        -- cec_binds
                -> WantedConstraints -> TcM ()
report_unsolved :: DiagnosticReason
-> DiagnosticReason
-> DiagnosticReason
-> DiagnosticReason
-> EvBindsVar
-> WantedConstraints
-> TcM ()
report_unsolved DiagnosticReason
type_errors DiagnosticReason
expr_holes
    DiagnosticReason
type_holes DiagnosticReason
out_of_scope_holes EvBindsVar
binds_var WantedConstraints
wanted
  | WantedConstraints -> Bool
isEmptyWC WantedConstraints
wanted
  = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()
  | Bool
otherwise
  = do { String -> SDoc -> TcM ()
traceTc String
"reportUnsolved {" (SDoc -> TcM ()) -> SDoc -> TcM ()
forall a b. (a -> b) -> a -> b
$
         [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"type errors:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> DiagnosticReason -> SDoc
forall a. Outputable a => a -> SDoc
ppr DiagnosticReason
type_errors
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"expr holes:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> DiagnosticReason -> SDoc
forall a. Outputable a => a -> SDoc
ppr DiagnosticReason
expr_holes
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"type holes:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> DiagnosticReason -> SDoc
forall a. Outputable a => a -> SDoc
ppr DiagnosticReason
type_holes
              , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"scope holes:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> DiagnosticReason -> SDoc
forall a. Outputable a => a -> SDoc
ppr DiagnosticReason
out_of_scope_holes ]
       ; String -> SDoc -> TcM ()
traceTc String
"reportUnsolved (before zonking and tidying)" (WantedConstraints -> SDoc
forall a. Outputable a => a -> SDoc
ppr WantedConstraints
wanted)

       ; wanted <- ZonkM WantedConstraints -> TcM WantedConstraints
forall a. ZonkM a -> TcM a
liftZonkM (ZonkM WantedConstraints -> TcM WantedConstraints)
-> ZonkM WantedConstraints -> TcM WantedConstraints
forall a b. (a -> b) -> a -> b
$ WantedConstraints -> ZonkM WantedConstraints
zonkWC WantedConstraints
wanted   -- Zonk to reveal all information

       ; let tidy_env = TidyEnv -> [TcId] -> TidyEnv
tidyFreeTyCoVars TidyEnv
emptyTidyEnv [TcId]
free_tvs
             free_tvs = (TcId -> Bool) -> [TcId] -> [TcId]
forall a. (a -> Bool) -> [a] -> [a]
filterOut TcId -> Bool
isCoVar ([TcId] -> [TcId]) -> [TcId] -> [TcId]
forall a b. (a -> b) -> a -> b
$
                        WantedConstraints -> [TcId]
tyCoVarsOfWCList WantedConstraints
wanted
                        -- tyCoVarsOfWC returns free coercion *holes*, even though
                        -- they are "bound" by other wanted constraints. They in
                        -- turn may mention variables bound further in, which makes
                        -- no sense. Really we should not return those holes at all;
                        -- for now we just filter them out.

       ; traceTc "reportUnsolved (after zonking):" $
         vcat [ text "Free tyvars:" <+> pprTyVars free_tvs
              , text "Tidy env:" <+> ppr tidy_env
              , text "Wanted:" <+> ppr wanted ]

       ; warn_redundant <- woptM Opt_WarnRedundantConstraints
       ; exp_syns <- goptM Opt_PrintExpandedSynonyms
       ; let err_ctxt = CEC { cec_encl :: [Implication]
cec_encl  = []
                            , cec_tidy :: TidyEnv
cec_tidy  = TidyEnv
tidy_env
                            , cec_defer_type_errors :: DiagnosticReason
cec_defer_type_errors = DiagnosticReason
type_errors
                            , cec_expr_holes :: DiagnosticReason
cec_expr_holes = DiagnosticReason
expr_holes
                            , cec_type_holes :: DiagnosticReason
cec_type_holes = DiagnosticReason
type_holes
                            , cec_out_of_scope_holes :: DiagnosticReason
cec_out_of_scope_holes = DiagnosticReason
out_of_scope_holes
                            , cec_suppress :: Bool
cec_suppress = WantedConstraints -> Bool
insolubleWC WantedConstraints
wanted
                                 -- See Note [Suppressing error messages]
                                 -- Suppress low-priority errors if there
                                 -- are insoluble errors anywhere;
                                 -- See #15539 and c.f. setting ic_status
                                 -- in GHC.Tc.Solver.setImplicationStatus
                            , cec_warn_redundant :: Bool
cec_warn_redundant = Bool
warn_redundant
                            , cec_expand_syns :: Bool
cec_expand_syns = Bool
exp_syns
                            , cec_binds :: EvBindsVar
cec_binds    = EvBindsVar
binds_var }

       ; tc_lvl <- getTcLevel
       ; reportWanteds err_ctxt tc_lvl wanted
       ; traceTc "reportUnsolved }" empty }

--------------------------------------------
--      Internal functions
--------------------------------------------

-- | Make a report from a single 'TcSolverReportMsg'.
important :: SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important :: SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important SolverReportErrCtxt
ctxt TcSolverReportMsg
doc
  = SolverReport { sr_important_msg :: SolverReportWithCtxt
sr_important_msg = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt TcSolverReportMsg
doc
                 , sr_supplementary :: [SolverReportSupplementary]
sr_supplementary = [] }

add_relevant_bindings :: RelevantBindings -> SolverReport -> SolverReport
add_relevant_bindings :: RelevantBindings -> SolverReport -> SolverReport
add_relevant_bindings RelevantBindings
binds report :: SolverReport
report@(SolverReport { sr_supplementary :: SolverReport -> [SolverReportSupplementary]
sr_supplementary = [SolverReportSupplementary]
supp })
  = SolverReport
report { sr_supplementary = SupplementaryBindings binds : supp }

-- | Returns True <=> the SolverReportErrCtxt indicates that something is deferred
deferringAnyBindings :: SolverReportErrCtxt -> Bool
  -- Don't check cec_type_holes, as these don't cause bindings to be deferred
deferringAnyBindings :: SolverReportErrCtxt -> Bool
deferringAnyBindings (CEC { cec_defer_type_errors :: SolverReportErrCtxt -> DiagnosticReason
cec_defer_type_errors  = DiagnosticReason
ErrorWithoutFlag
                          , cec_expr_holes :: SolverReportErrCtxt -> DiagnosticReason
cec_expr_holes         = DiagnosticReason
ErrorWithoutFlag
                          , cec_out_of_scope_holes :: SolverReportErrCtxt -> DiagnosticReason
cec_out_of_scope_holes = DiagnosticReason
ErrorWithoutFlag }) = Bool
False
deferringAnyBindings SolverReportErrCtxt
_                                                   = Bool
True

maybeSwitchOffDefer :: EvBindsVar -> SolverReportErrCtxt -> SolverReportErrCtxt
-- Switch off defer-type-errors inside CoEvBindsVar
-- See Note [Failing equalities with no evidence bindings]
maybeSwitchOffDefer :: EvBindsVar -> SolverReportErrCtxt -> SolverReportErrCtxt
maybeSwitchOffDefer EvBindsVar
evb SolverReportErrCtxt
ctxt
 | CoEvBindsVar{} <- EvBindsVar
evb
 = SolverReportErrCtxt
ctxt { cec_defer_type_errors  = ErrorWithoutFlag
        , cec_expr_holes         = ErrorWithoutFlag
        , cec_out_of_scope_holes = ErrorWithoutFlag }
 | Bool
otherwise
 = SolverReportErrCtxt
ctxt

{- Note [Failing equalities with no evidence bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we go inside an implication that has no term evidence
(e.g. unifying under a forall), we can't defer type errors.  You could
imagine using the /enclosing/ bindings (in cec_binds), but that may
not have enough stuff in scope for the bindings to be well typed.  So
we just switch off deferred type errors altogether.  See #14605.

This is done by maybeSwitchOffDefer.  It's also useful in one other
place: see Note [Wrapping failing kind equalities] in GHC.Tc.Solver.

Note [Suppressing error messages]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The cec_suppress flag says "don't report any errors".  Instead, just create
evidence bindings (as usual).  It's used when more important errors have occurred.

Specifically (see reportWanteds)
  * If there are insoluble Givens, then we are in unreachable code and all bets
    are off.  So don't report any further errors.
  * If there are any insolubles (eg Int~Bool), here or in a nested implication,
    then suppress errors from the simple constraints here.  Sometimes the
    simple-constraint errors are a knock-on effect of the insolubles.

This suppression behaviour is controlled by the Bool flag in
ReportErrorSpec, as used in reportWanteds.

But we need to take care: flags can turn errors into warnings, and we
don't want those warnings to suppress subsequent errors (including
suppressing the essential addTcEvBind for them: #15152). So in
tryReporter we use askNoErrs to see if any error messages were
/actually/ produced; if not, we don't switch on suppression.

A consequence is that warnings never suppress warnings, so turning an
error into a warning may allow subsequent warnings to appear that were
previously suppressed.   (e.g. partial-sigs/should_fail/T14584)
-}

reportImplic :: SolverReportErrCtxt -> Implication -> TcM ()
reportImplic :: SolverReportErrCtxt -> Implication -> TcM ()
reportImplic SolverReportErrCtxt
ctxt implic :: Implication
implic@(Implic { ic_skols :: Implication -> [TcId]
ic_skols  = [TcId]
tvs
                                 , ic_given :: Implication -> [TcId]
ic_given  = [TcId]
given
                                 , ic_wanted :: Implication -> WantedConstraints
ic_wanted = WantedConstraints
wanted, ic_binds :: Implication -> EvBindsVar
ic_binds = EvBindsVar
evb
                                 , ic_status :: Implication -> ImplicStatus
ic_status = ImplicStatus
status, ic_info :: Implication -> SkolemInfoAnon
ic_info = SkolemInfoAnon
info
                                 , ic_env :: Implication -> CtLocEnv
ic_env    = CtLocEnv
ct_loc_env
                                 , ic_tclvl :: Implication -> TcLevel
ic_tclvl  = TcLevel
tc_lvl })
  | SkolemInfoAnon
BracketSkol <- SkolemInfoAnon
info
  , Bool -> Bool
not Bool
insoluble
  = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()        -- For Template Haskell brackets report only
                     -- definite errors. The whole thing will be re-checked
                     -- later when we plug it in, and meanwhile there may
                     -- certainly be un-satisfied constraints

  | Bool
otherwise
  = do { String -> SDoc -> TcM ()
traceTc String
"reportImplic" (SDoc -> TcM ()) -> SDoc -> TcM ()
forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat
           [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"tidy env:"   SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> TidyEnv -> SDoc
forall a. Outputable a => a -> SDoc
ppr (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt)
           , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"skols:     " SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [TcId] -> SDoc
pprTyVars [TcId]
tvs
           , String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"tidy skols:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> [TcId] -> SDoc
pprTyVars [TcId]
tvs' ]

       ; Bool -> TcM () -> TcM ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when Bool
bad_telescope (TcM () -> TcM ()) -> TcM () -> TcM ()
forall a b. (a -> b) -> a -> b
$ SolverReportErrCtxt
-> CtLocEnv -> SkolemInfoAnon -> [TcId] -> TcM ()
reportBadTelescope SolverReportErrCtxt
ctxt CtLocEnv
ct_loc_env SkolemInfoAnon
info [TcId]
tvs
               -- Do /not/ use the tidied tvs because then are in the
               -- wrong order, so tidying will rename things wrongly
       ; SolverReportErrCtxt -> TcLevel -> WantedConstraints -> TcM ()
reportWanteds SolverReportErrCtxt
ctxt' TcLevel
tc_lvl WantedConstraints
wanted

       -- Report redundant (unused) constraints
       ; SolverReportErrCtxt
-> CtLocEnv -> SkolemInfoAnon -> [TcId] -> TcM ()
warnRedundantConstraints SolverReportErrCtxt
ctxt' CtLocEnv
ct_loc_env SkolemInfoAnon
info' [TcId]
dead_givens }
  where
    insoluble :: Bool
insoluble    = ImplicStatus -> Bool
isInsolubleStatus ImplicStatus
status
    (TidyEnv
env1, [TcId]
tvs') = TidyEnv -> [TcId] -> (TidyEnv, [TcId])
tidyVarBndrs (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt) ([TcId] -> (TidyEnv, [TcId])) -> [TcId] -> (TidyEnv, [TcId])
forall a b. (a -> b) -> a -> b
$
                   [TcId] -> [TcId]
scopedSort [TcId]
tvs
        -- scopedSort: the ic_skols may not be in dependency order
        -- (see Note [Skolems in an implication] in GHC.Tc.Types.Constraint)
        -- but tidying goes wrong on out-of-order constraints;
        -- so we sort them here before tidying
    info' :: SkolemInfoAnon
info'   = TidyEnv -> SkolemInfoAnon -> SkolemInfoAnon
tidySkolemInfoAnon TidyEnv
env1 SkolemInfoAnon
info
    implic' :: Implication
implic' = Implication
implic { ic_skols = tvs'
                     , ic_given = map (tidyEvVar env1) given
                     , ic_info  = info' }

    ctxt1 :: SolverReportErrCtxt
ctxt1 = EvBindsVar -> SolverReportErrCtxt -> SolverReportErrCtxt
maybeSwitchOffDefer EvBindsVar
evb SolverReportErrCtxt
ctxt
    ctxt' :: SolverReportErrCtxt
ctxt' = SolverReportErrCtxt
ctxt1 { cec_tidy     = env1
                  , cec_encl     = implic' : cec_encl ctxt

                  , cec_suppress = insoluble || cec_suppress ctxt
                        -- Suppress inessential errors if there
                        -- are insolubles anywhere in the
                        -- tree rooted here, or we've come across
                        -- a suppress-worthy constraint higher up (#11541)

                  , cec_binds    = evb }

    dead_givens :: [TcId]
dead_givens = case ImplicStatus
status of
                    IC_Solved { ics_dead :: ImplicStatus -> [TcId]
ics_dead = [TcId]
dead } -> [TcId]
dead
                    ImplicStatus
_                             -> []

    bad_telescope :: Bool
bad_telescope = case ImplicStatus
status of
              ImplicStatus
IC_BadTelescope -> Bool
True
              ImplicStatus
_               -> Bool
False

warnRedundantConstraints :: SolverReportErrCtxt -> CtLocEnv -> SkolemInfoAnon -> [EvVar] -> TcM ()
-- See Note [Tracking redundant constraints] in GHC.Tc.Solver
warnRedundantConstraints :: SolverReportErrCtxt
-> CtLocEnv -> SkolemInfoAnon -> [TcId] -> TcM ()
warnRedundantConstraints SolverReportErrCtxt
ctxt CtLocEnv
env SkolemInfoAnon
info [TcId]
redundant_evs
 | Bool -> Bool
not (SolverReportErrCtxt -> Bool
cec_warn_redundant SolverReportErrCtxt
ctxt)
 = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

 | [TcId] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TcId]
redundant_evs
 = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

 -- Do not report redundant constraints for quantified constraints
 -- See (RC4) in Note [Tracking redundant constraints]
 -- Fortunately it is easy to spot implications constraints that arise
 -- from quantified constraints, from their SkolInfo
 | InstSkol (IsQC {}) PatersonSize
_ <- SkolemInfoAnon
info
 = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()

 | SigSkol UserTypeCtxt
user_ctxt Type
_ [(Name, TcId)]
_ <- SkolemInfoAnon
info
 -- When dealing with a user-written type signature,
 -- we want to add "In the type signature for f".
 = Bool -> CtLocEnv -> TcM ()
report_redundant_msg Bool
True (CtLocEnv -> SrcSpan -> CtLocEnv
setCtLocEnvLoc CtLocEnv
env (UserTypeCtxt -> SrcSpan
redundantConstraintsSpan UserTypeCtxt
user_ctxt))
                             --  ^^^^ add "In the type signature..."

 | Bool
otherwise
 -- But for InstSkol there already *is* a surrounding
 -- "In the instance declaration for Eq [a]" context
 -- and we don't want to say it twice. Seems a bit ad-hoc
 = Bool -> CtLocEnv -> TcM ()
report_redundant_msg Bool
False CtLocEnv
env
                   --   ^^^^^ don't add "In the type signature..."
 where
   report_redundant_msg :: Bool -- whether to add "In the type signature..." to the diagnostic
                        -> CtLocEnv
                        -> TcRn ()
   report_redundant_msg :: Bool -> CtLocEnv -> TcM ()
report_redundant_msg Bool
show_info CtLocEnv
lcl_env
     = do { msg <-
              CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport
                CtLocEnv
lcl_env
                ([TcId] -> (SkolemInfoAnon, Bool) -> TcRnMessage
TcRnRedundantConstraints [TcId]
redundant_evs (SkolemInfoAnon
info, Bool
show_info))
                (SolverReportErrCtxt -> Maybe SolverReportErrCtxt
forall a. a -> Maybe a
Just SolverReportErrCtxt
ctxt)
                []
          ; reportDiagnostic msg }

reportBadTelescope :: SolverReportErrCtxt -> CtLocEnv -> SkolemInfoAnon -> [TcTyVar] -> TcM ()
reportBadTelescope :: SolverReportErrCtxt
-> CtLocEnv -> SkolemInfoAnon -> [TcId] -> TcM ()
reportBadTelescope SolverReportErrCtxt
ctxt CtLocEnv
env (ForAllSkol TyVarBndrs
telescope) [TcId]
skols
  = do { msg <- CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport
                  CtLocEnv
env
                  (SolverReportWithCtxt -> DiagnosticReason -> TcRnMessage
TcRnSolverReport SolverReportWithCtxt
report DiagnosticReason
ErrorWithoutFlag)
                  (SolverReportErrCtxt -> Maybe SolverReportErrCtxt
forall a. a -> Maybe a
Just SolverReportErrCtxt
ctxt)
                  []
       ; reportDiagnostic msg }
  where
    report :: SolverReportWithCtxt
report = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt (TcSolverReportMsg -> SolverReportWithCtxt)
-> TcSolverReportMsg -> SolverReportWithCtxt
forall a b. (a -> b) -> a -> b
$ TyVarBndrs -> [TcId] -> TcSolverReportMsg
BadTelescope TyVarBndrs
telescope [TcId]
skols

reportBadTelescope SolverReportErrCtxt
_ CtLocEnv
_ SkolemInfoAnon
skol_info [TcId]
skols
  = String -> SDoc -> TcM ()
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"reportBadTelescope" (SkolemInfoAnon -> SDoc
forall a. Outputable a => a -> SDoc
ppr SkolemInfoAnon
skol_info SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [TcId] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TcId]
skols)

-- | Should we completely ignore this constraint in error reporting?
-- It *must* be the case that any constraint for which this returns True
-- somehow causes an error to be reported elsewhere.
-- See Note [Constraints to ignore].
ignoreConstraint :: Ct -> Bool
ignoreConstraint :: Ct -> Bool
ignoreConstraint Ct
ct
  | CtOrigin
AssocFamPatOrigin <- Ct -> CtOrigin
ctOrigin Ct
ct
  = Bool
True
  | Bool
otherwise
  = Bool
False

-- | Makes an error item from a constraint, calculating whether or not
-- the item should be suppressed. See Note [Wanteds rewrite Wanteds]
-- in GHC.Tc.Types.Constraint. Returns Nothing if we should just ignore
-- a constraint. See Note [Constraints to ignore].
mkErrorItem :: Ct -> TcM (Maybe ErrorItem)
mkErrorItem :: Ct -> TcM (Maybe ErrorItem)
mkErrorItem Ct
ct
  | Ct -> Bool
ignoreConstraint Ct
ct
  = do { String -> SDoc -> TcM ()
traceTc String
"Ignoring constraint:" (Ct -> SDoc
forall a. Outputable a => a -> SDoc
ppr Ct
ct)
       ; Maybe ErrorItem -> TcM (Maybe ErrorItem)
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe ErrorItem
forall a. Maybe a
Nothing }   -- See Note [Constraints to ignore]

  | Bool
otherwise
  = do { let loc :: CtLoc
loc = Ct -> CtLoc
ctLoc Ct
ct
             flav :: CtFlavour
flav = Ct -> CtFlavour
ctFlavour Ct
ct

       ; (suppress, m_evdest) <- case Ct -> CtEvidence
ctEvidence Ct
ct of
           CtGiven {} -> (Bool, Maybe TcEvDest)
-> IOEnv (Env TcGblEnv TcLclEnv) (Bool, Maybe TcEvDest)
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (Bool
False, Maybe TcEvDest
forall a. Maybe a
Nothing)
           CtWanted { ctev_rewriters :: CtEvidence -> RewriterSet
ctev_rewriters = RewriterSet
rewriters, ctev_dest :: CtEvidence -> TcEvDest
ctev_dest = TcEvDest
dest }
             -> do { rewriters' <- RewriterSet -> TcM RewriterSet
zonkRewriterSet RewriterSet
rewriters
                   ; return (not (isEmptyRewriterSet rewriters'), Just dest) }

       ; let m_reason = case Ct
ct of
                CIrredCan (IrredCt { ir_reason :: IrredCt -> CtIrredReason
ir_reason = CtIrredReason
reason }) -> CtIrredReason -> Maybe CtIrredReason
forall a. a -> Maybe a
Just CtIrredReason
reason
                Ct
_                                          -> Maybe CtIrredReason
forall a. Maybe a
Nothing

       ; return $ Just $ EI { ei_pred     = ctPred ct
                            , ei_evdest   = m_evdest
                            , ei_flavour  = flav
                            , ei_loc      = loc
                            , ei_m_reason = m_reason
                            , ei_suppress = suppress }}

-- | Actually report this 'ErrorItem'.
unsuppressErrorItem :: ErrorItem -> ErrorItem
unsuppressErrorItem :: ErrorItem -> ErrorItem
unsuppressErrorItem ErrorItem
ei = ErrorItem
ei { ei_suppress = False }

----------------------------------------------------------------
reportWanteds :: SolverReportErrCtxt -> TcLevel -> WantedConstraints -> TcM ()
reportWanteds :: SolverReportErrCtxt -> TcLevel -> WantedConstraints -> TcM ()
reportWanteds SolverReportErrCtxt
ctxt TcLevel
tc_lvl wc :: WantedConstraints
wc@(WC { wc_simple :: WantedConstraints -> Cts
wc_simple = Cts
simples, wc_impl :: WantedConstraints -> Bag Implication
wc_impl = Bag Implication
implics
                                 , wc_errors :: WantedConstraints -> Bag DelayedError
wc_errors = Bag DelayedError
errs })
  | WantedConstraints -> Bool
isEmptyWC WantedConstraints
wc = String -> SDoc -> TcM ()
traceTc String
"reportWanteds empty WC" SDoc
forall doc. IsOutput doc => doc
empty
  | Bool
otherwise
  = do { tidy_items1 <- (Ct -> TcM (Maybe ErrorItem))
-> [Ct] -> IOEnv (Env TcGblEnv TcLclEnv) [ErrorItem]
forall (m :: * -> *) a b.
Applicative m =>
(a -> m (Maybe b)) -> [a] -> m [b]
mapMaybeM Ct -> TcM (Maybe ErrorItem)
mkErrorItem [Ct]
tidy_cts
       ; traceTc "reportWanteds 1" (vcat [ text "Simples =" <+> ppr simples
                                         , text "Suppress =" <+> ppr (cec_suppress ctxt)
                                         , text "tidy_cts   =" <+> ppr tidy_cts
                                         , text "tidy_items1 =" <+> ppr tidy_items1
                                         , text "tidy_errs =" <+> ppr tidy_errs ])

         -- Catch an awkward (and probably rare) case in which /all/ errors are
         -- suppressed: see Wrinkle (WRW2) in Note [Prioritise Wanteds with empty
         -- RewriterSet] in GHC.Tc.Types.Constraint.
         --
         -- Unless we are sure that an error will be reported some other way
         -- (details in the defn of tidy_items) un-suppress the lot. This makes
         -- sure we don't forget to report an error at all, which is
         -- catastrophic: GHC proceeds to desguar and optimise the program, even
         -- though it is full of type errors (#22702, #22793)
       ; errs_already <- ifErrsM (return True) (return False)
       ; let tidy_items
               | Bool -> Bool
not Bool
errs_already                     -- Have not already reported an error (perhaps
                                                      --   from an outer implication); see #21405
               , Bool -> Bool
not ((Ct -> Bool) -> Cts -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any Ct -> Bool
ignoreConstraint Cts
simples)   -- No error is ignorable (is reported elsewhere)
               , (ErrorItem -> Bool) -> [ErrorItem] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all ErrorItem -> Bool
ei_suppress [ErrorItem]
tidy_items1          -- All errors are suppressed
               = (ErrorItem -> ErrorItem) -> [ErrorItem] -> [ErrorItem]
forall a b. (a -> b) -> [a] -> [b]
map ErrorItem -> ErrorItem
unsuppressErrorItem [ErrorItem]
tidy_items1
               | Bool
otherwise
               = [ErrorItem]
tidy_items1

         -- First, deal with any out-of-scope errors:
       ; let (out_of_scope, other_holes, not_conc_errs) = partition_errors tidy_errs
               -- don't suppress out-of-scope errors
             ctxt_for_scope_errs = SolverReportErrCtxt
ctxt { cec_suppress = False }
       ; (_, no_out_of_scope) <- askNoErrs $
                                 reportHoles tidy_items ctxt_for_scope_errs out_of_scope

         -- Next, deal with things that are utterly wrong
         -- Like Int ~ Bool (incl nullary TyCons)
         -- or  Int ~ t a   (AppTy on one side)
         -- These /ones/ are not suppressed by the incoming context
         -- (but will be by out-of-scope errors)
       ; let ctxt_for_insols = SolverReportErrCtxt
ctxt { cec_suppress = not no_out_of_scope }
       ; reportHoles tidy_items ctxt_for_insols other_holes
          -- holes never suppress

       ; reportNotConcreteErrs ctxt_for_insols not_conc_errs

          -- See Note [Suppressing confusing errors]
       ; let (suppressed_items, items0) = partition suppress tidy_items
       ; traceTc "reportWanteds suppressed:" (ppr suppressed_items)
       ; (ctxt1, items1) <- tryReporters ctxt_for_insols report1 items0

         -- Now all the other constraints.  We suppress errors here if
         -- any of the first batch failed, or if the enclosing context
         -- says to suppress
       ; let ctxt2 = SolverReportErrCtxt
ctxt1 { cec_suppress = cec_suppress ctxt || cec_suppress ctxt1 }
       ; (ctxt3, leftovers) <- tryReporters ctxt2 report2 items1
       ; massertPpr (null leftovers)
           (text "The following unsolved Wanted constraints \
                 \have not been reported to the user:"
           $$ ppr leftovers)

       ; mapBagM_ (reportImplic ctxt2) implics
            -- NB ctxt2: don't suppress inner insolubles if there's only a
            -- wanted insoluble here; but do suppress inner insolubles
            -- if there's a *given* insoluble here (= inaccessible code)

            -- Only now, if there are no errors, do we report suppressed ones
            -- See Note [Suppressing confusing errors]
            -- We don't need to update the context further because of the
            -- whenNoErrs guard
       ; whenNoErrs $
         do { (_, more_leftovers) <- tryReporters ctxt3 report3 suppressed_items
            ; massertPpr (null more_leftovers) (ppr more_leftovers) } }
 where
    env :: TidyEnv
env       = SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt
    tidy_cts :: [Ct]
tidy_cts  = Cts -> [Ct]
forall a. Bag a -> [a]
bagToList ((Ct -> Ct) -> Cts -> Cts
forall a b. (a -> b) -> Bag a -> Bag b
mapBag (TidyEnv -> Ct -> Ct
tidyCt TidyEnv
env)   Cts
simples)
    tidy_errs :: [DelayedError]
tidy_errs = Bag DelayedError -> [DelayedError]
forall a. Bag a -> [a]
bagToList ((DelayedError -> DelayedError)
-> Bag DelayedError -> Bag DelayedError
forall a b. (a -> b) -> Bag a -> Bag b
mapBag (TidyEnv -> DelayedError -> DelayedError
tidyDelayedError TidyEnv
env) Bag DelayedError
errs)

    partition_errors :: [DelayedError] -> ([Hole], [Hole], [NotConcreteError])
    partition_errors :: [DelayedError] -> ([Hole], [Hole], [NotConcreteError])
partition_errors = [Hole]
-> [Hole]
-> [NotConcreteError]
-> [DelayedError]
-> ([Hole], [Hole], [NotConcreteError])
go [] [] []
      where
        go :: [Hole]
-> [Hole]
-> [NotConcreteError]
-> [DelayedError]
-> ([Hole], [Hole], [NotConcreteError])
go [Hole]
out_of_scope [Hole]
other_holes [NotConcreteError]
syn_eqs []
          = ([Hole]
out_of_scope, [Hole]
other_holes, [NotConcreteError]
syn_eqs)
        go [Hole]
es1 [Hole]
es2 [NotConcreteError]
es3 (DelayedError
err:[DelayedError]
errs)
          | ([Hole]
es1, [Hole]
es2, [NotConcreteError]
es3) <- [Hole]
-> [Hole]
-> [NotConcreteError]
-> [DelayedError]
-> ([Hole], [Hole], [NotConcreteError])
go [Hole]
es1 [Hole]
es2 [NotConcreteError]
es3 [DelayedError]
errs
          = case DelayedError
err of
              DE_Hole Hole
hole
                | Hole -> Bool
isOutOfScopeHole Hole
hole
                -> (Hole
hole Hole -> [Hole] -> [Hole]
forall a. a -> [a] -> [a]
: [Hole]
es1, [Hole]
es2, [NotConcreteError]
es3)
                | Bool
otherwise
                -> ([Hole]
es1, Hole
hole Hole -> [Hole] -> [Hole]
forall a. a -> [a] -> [a]
: [Hole]
es2, [NotConcreteError]
es3)
              DE_NotConcrete NotConcreteError
err
                -> ([Hole]
es1, [Hole]
es2, NotConcreteError
err NotConcreteError -> [NotConcreteError] -> [NotConcreteError]
forall a. a -> [a] -> [a]
: [NotConcreteError]
es3)

      -- See Note [Suppressing confusing errors]
    suppress :: ErrorItem -> Bool
    suppress :: ErrorItem -> Bool
suppress ErrorItem
item
      | CtFlavour
Wanted <- ErrorItem -> CtFlavour
ei_flavour ErrorItem
item
      = ErrorItem -> Bool
is_ww_fundep_item ErrorItem
item
      | Bool
otherwise
      = Bool
False

    -- report1: ones that should *not* be suppressed by
    --          an insoluble somewhere else in the tree
    -- It's crucial that anything that is considered insoluble
    -- (see GHC.Tc.Utils.insolublWantedCt) is caught here, otherwise
    -- we might suppress its error message, and proceed on past
    -- type checking to get a Lint error later
    report1 :: [ReporterSpec]
report1 = [ (String
"custom_error", ErrorItem -> Pred -> Bool
forall {p}. ErrorItem -> p -> Bool
is_user_type_error, Bool
True,  Reporter
mkUserTypeErrorReporter)
                 -- (Handles TypeError and Unsatisfiable)

              , ReporterSpec
given_eq_spec
              , (String
"insoluble2",      ErrorItem -> Pred -> Bool
forall {p}. p -> Pred -> Bool
utterly_wrong,  Bool
True, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr)
              , (String
"skolem eq1",      ErrorItem -> Pred -> Bool
very_wrong,     Bool
True, Reporter
mkSkolReporter)
              , (String
"FixedRuntimeRep", ErrorItem -> Pred -> Bool
is_FRR,         Bool
True, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter HasDebugCallStack =>
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkFRRErr)
              , (String
"skolem eq2",      ErrorItem -> Pred -> Bool
skolem_eq,      Bool
True, Reporter
mkSkolReporter)
              , (String
"non-tv eq",       ErrorItem -> Pred -> Bool
forall {p}. p -> Pred -> Bool
non_tv_eq,      Bool
True, Reporter
mkSkolReporter)

                  -- The only remaining equalities are alpha ~ ty,
                  -- where alpha is untouchable; and representational equalities
                  -- Prefer homogeneous equalities over hetero, because the
                  -- former might be holding up the latter.
                  -- See Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality
              , (String
"Homo eqs",      ErrorItem -> Pred -> Bool
forall {p}. p -> Pred -> Bool
is_homo_equality,  Bool
True,  (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr)
              , (String
"Other eqs",     ErrorItem -> Pred -> Bool
is_equality,       Bool
True,  (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr)
              ]

    -- report2: we suppress these if there are insolubles elsewhere in the tree
    report2 :: [ReporterSpec]
report2 = [ (String
"Implicit params", ErrorItem -> Pred -> Bool
is_ip,           Bool
False, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkIPErr)
              , (String
"Irreds",          ErrorItem -> Pred -> Bool
is_irred,        Bool
False, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkIrredErr)
              , (String
"Dicts",           ErrorItem -> Pred -> Bool
is_dict,         Bool
False, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter HasDebugCallStack =>
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkDictErr) ]

    -- report3: suppressed errors should be reported as categorized by either report1
    -- or report2. Keep this in sync with the suppress function above
    report3 :: [(String, ErrorItem -> p -> Bool, Bool, Reporter)]
report3 = [ (String
"wanted/wanted fundeps", ErrorItem -> p -> Bool
forall {p}. ErrorItem -> p -> Bool
is_ww_fundep, Bool
True, (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr)
              ]

    -- rigid_nom_eq, rigid_nom_tv_eq,
    is_dict, is_equality, is_ip, is_FRR, is_irred :: ErrorItem -> Pred -> Bool

    is_given_eq :: ErrorItem -> Pred -> Bool
is_given_eq ErrorItem
item Pred
pred
       | CtFlavour
Given <- ErrorItem -> CtFlavour
ei_flavour ErrorItem
item
       , EqPred {} <- Pred
pred = Bool
True
       | Bool
otherwise         = Bool
False
       -- I think all given residuals are equalities

    -- Things like (Int ~N Bool)
    utterly_wrong :: p -> Pred -> Bool
utterly_wrong p
_ (EqPred EqRel
NomEq Type
ty1 Type
ty2) = Type -> Bool
isRigidTy Type
ty1 Bool -> Bool -> Bool
&& Type -> Bool
isRigidTy Type
ty2
    utterly_wrong p
_ Pred
_                      = Bool
False

    -- Things like (a ~N Int)
    very_wrong :: ErrorItem -> Pred -> Bool
very_wrong ErrorItem
_ (EqPred EqRel
NomEq Type
ty1 Type
ty2) = TcLevel -> Type -> Bool
isSkolemTy TcLevel
tc_lvl Type
ty1 Bool -> Bool -> Bool
&& Type -> Bool
isRigidTy Type
ty2
    very_wrong ErrorItem
_ Pred
_                      = Bool
False

    -- Representation-polymorphism errors, to be reported using mkFRRErr.
    is_FRR :: ErrorItem -> Pred -> Bool
is_FRR ErrorItem
item Pred
_ = Maybe FixedRuntimeRepErrorInfo -> Bool
forall a. Maybe a -> Bool
isJust (Maybe FixedRuntimeRepErrorInfo -> Bool)
-> Maybe FixedRuntimeRepErrorInfo -> Bool
forall a b. (a -> b) -> a -> b
$ HasDebugCallStack => ErrorItem -> Maybe FixedRuntimeRepErrorInfo
ErrorItem -> Maybe FixedRuntimeRepErrorInfo
fixedRuntimeRepOrigin_maybe ErrorItem
item

    -- Things like (a ~N b) or (a  ~N  F Bool)
    skolem_eq :: ErrorItem -> Pred -> Bool
skolem_eq ErrorItem
_ (EqPred EqRel
NomEq Type
ty1 Type
_) = TcLevel -> Type -> Bool
isSkolemTy TcLevel
tc_lvl Type
ty1
    skolem_eq ErrorItem
_ Pred
_                    = Bool
False

    -- Things like (F a  ~N  Int)
    non_tv_eq :: p -> Pred -> Bool
non_tv_eq p
_ (EqPred EqRel
NomEq Type
ty1 Type
_) = Bool -> Bool
not (Type -> Bool
isTyVarTy Type
ty1)
    non_tv_eq p
_ Pred
_                    = Bool
False

    -- Catch TypeError and Unsatisfiable.
    -- Here, we want any nested TypeErrors to bubble up, so we use
    -- 'containsUserTypeError' and not 'isTopLevelUserTypeError'.
    --
    -- See also Note [Implementation of Unsatisfiable constraints], point (F).
    is_user_type_error :: ErrorItem -> p -> Bool
is_user_type_error ErrorItem
item p
_ = Type -> Bool
containsUserTypeError (ErrorItem -> Type
errorItemPred ErrorItem
item)

    is_homo_equality :: p -> Pred -> Bool
is_homo_equality p
_ (EqPred EqRel
_ Type
ty1 Type
ty2)
      = HasDebugCallStack => Type -> Type
Type -> Type
typeKind Type
ty1 HasDebugCallStack => Type -> Type -> Bool
Type -> Type -> Bool
`tcEqType` HasDebugCallStack => Type -> Type
Type -> Type
typeKind Type
ty2
    is_homo_equality p
_ Pred
_
      = Bool
False

    is_equality :: ErrorItem -> Pred -> Bool
is_equality ErrorItem
_(EqPred {}) = Bool
True
    is_equality ErrorItem
_ Pred
_          = Bool
False

    is_dict :: ErrorItem -> Pred -> Bool
is_dict ErrorItem
_ (ClassPred {}) = Bool
True
    is_dict ErrorItem
_ Pred
_              = Bool
False

    is_ip :: ErrorItem -> Pred -> Bool
is_ip ErrorItem
_ (ClassPred Class
cls [Type]
_) = Class -> Bool
isIPClass Class
cls
    is_ip ErrorItem
_ Pred
_                 = Bool
False

    is_irred :: ErrorItem -> Pred -> Bool
is_irred ErrorItem
_ (IrredPred {}) = Bool
True
    is_irred ErrorItem
_ Pred
_              = Bool
False

     -- See situation (1) of Note [Suppressing confusing errors]
    is_ww_fundep :: ErrorItem -> p -> Bool
is_ww_fundep ErrorItem
item p
_ = ErrorItem -> Bool
is_ww_fundep_item ErrorItem
item
    is_ww_fundep_item :: ErrorItem -> Bool
is_ww_fundep_item = CtOrigin -> Bool
isWantedWantedFunDepOrigin (CtOrigin -> Bool) -> (ErrorItem -> CtOrigin) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> CtOrigin
errorItemOrigin

    given_eq_spec :: ReporterSpec
given_eq_spec  -- See Note [Given errors]
      | Bool
has_gadt_match_here
      = (String
"insoluble1a", ErrorItem -> Pred -> Bool
is_given_eq, Bool
True,  Reporter
mkGivenErrorReporter)
      | Bool
otherwise
      = (String
"insoluble1b", ErrorItem -> Pred -> Bool
is_given_eq, Bool
False, Reporter
ignoreErrorReporter)
          -- False means don't suppress subsequent errors
          -- Reason: we don't report all given errors
          --         (see mkGivenErrorReporter), and we should only suppress
          --         subsequent errors if we actually report this one!
          --         #13446 is an example

    -- See Note [Given errors]
    has_gadt_match_here :: Bool
has_gadt_match_here = [Implication] -> Bool
has_gadt_match (SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt)
    has_gadt_match :: [Implication] -> Bool
has_gadt_match [] = Bool
False
    has_gadt_match (Implication
implic : [Implication]
implics)
      | PatSkol {} <- Implication -> SkolemInfoAnon
ic_info Implication
implic
      , Implication -> HasGivenEqs
ic_given_eqs Implication
implic HasGivenEqs -> HasGivenEqs -> Bool
forall a. Eq a => a -> a -> Bool
/= HasGivenEqs
NoGivenEqs
      , Implication -> Bool
ic_warn_inaccessible Implication
implic
          -- Don't bother doing this if -Winaccessible-code isn't enabled.
          -- See Note [Avoid -Winaccessible-code when deriving] in GHC.Tc.TyCl.Instance.
      = Bool
True
      | Bool
otherwise
      = [Implication] -> Bool
has_gadt_match [Implication]
implics

---------------
isSkolemTy :: TcLevel -> Type -> Bool
-- The type is a skolem tyvar
isSkolemTy :: TcLevel -> Type -> Bool
isSkolemTy TcLevel
tc_lvl Type
ty
  | Just TcId
tv <- Type -> Maybe TcId
getTyVar_maybe Type
ty
  =  TcId -> Bool
isSkolemTyVar TcId
tv
  Bool -> Bool -> Bool
|| (TcId -> Bool
isTyVarTyVar TcId
tv Bool -> Bool -> Bool
&& TcLevel -> TcId -> Bool
isTouchableMetaTyVar TcLevel
tc_lvl TcId
tv)
     -- The last case is for touchable TyVarTvs
     -- we postpone untouchables to a latter test (too obscure)

  | Bool
otherwise
  = Bool
False

isTyFun_maybe :: Type -> Maybe TyCon
isTyFun_maybe :: Type -> Maybe TyCon
isTyFun_maybe Type
ty = case HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty of
                      Just (TyCon
tc,[Type]
_) | TyCon -> Bool
isTypeFamilyTyCon TyCon
tc -> TyCon -> Maybe TyCon
forall a. a -> Maybe a
Just TyCon
tc
                      Maybe (TyCon, [Type])
_ -> Maybe TyCon
forall a. Maybe a
Nothing

{- Note [Suppressing confusing errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Certain errors we might encounter are potentially confusing to users.
If there are any other errors to report, at all, we want to suppress these.

Which errors (only 1 case right now):

1) Errors which arise from the interaction of two Wanted fun-dep constraints.
   Example:

     class C a b | a -> b where
       op :: a -> b -> b

     foo _ = op True Nothing

     bar _ = op False []

   Here, we could infer
     foo :: C Bool (Maybe a) => p -> Maybe a
     bar :: C Bool [a]       => p -> [a]

   (The unused arguments suppress the monomorphism restriction.) The problem
   is that these types can't both be correct, as they violate the functional
   dependency. Yet reporting an error here is awkward: we must
   non-deterministically choose either foo or bar to reject. We thus want
   to report this problem only when there is nothing else to report.
   See typecheck/should_fail/T13506 for an example of when to suppress
   the error. The case above is actually accepted, because foo and bar
   are checked separately, and thus the two fundep constraints never
   encounter each other. It is test case typecheck/should_compile/FunDepOrigin1.

   This case applies only when both fundeps are *Wanted* fundeps; when
   both are givens, the error represents unreachable code. For
   a Given/Wanted case, see #9612.

Mechanism:

We use the `suppress` function within reportWanteds to filter out these two
cases, then report all other errors. Lastly, we return to these suppressed
ones and report them only if there have been no errors so far.

Note [Constraints to ignore]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some constraints are meant only to aid the solver by unification; a failure
to solve them is not necessarily an error to report to the user. It is critical
that compilation is aborted elsewhere if there are any ignored constraints here;
they will remain unfilled, and might have been used to rewrite another constraint.

Currently, the constraints to ignore are:

1) Constraints generated in order to unify associated type instance parameters
   with class parameters. Here are two illustrative examples:

     class C (a :: k) where
       type F (b :: k)

     instance C True where
       type F a = Int

     instance C Left where
       type F (Left :: a -> Either a b) = Bool

   In the first instance, we want to infer that `a` has type Bool. So we emit
   a constraint unifying kappa (the guessed type of `a`) with Bool. All is well.

   In the second instance, we process the associated type instance only
   after fixing the quantified type variables of the class instance. We thus
   have skolems a1 and b1 such that the class instance is for (Left :: a1 -> Either a1 b1).
   Unifying a1 and b1 with a and b in the type instance will fail, but harmlessly so.
   checkConsistentFamInst checks for this, and will fail if anything has gone
   awry. Really the equality constraints emitted are just meant as an aid, not
   a requirement. This is test case T13972.

   We detect this case by looking for an origin of AssocFamPatOrigin; constraints
   with this origin are dropped entirely during error message reporting.

   If there is any trouble, checkValidFamInst bleats, aborting compilation.

Note [Implementation of Unsatisfiable constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Unsatisfiable constraint was introduced in GHC proposal #433 (https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0433-unsatisfiable.rst).
See Note [The Unsatisfiable constraint] in GHC.TypeError.

Its implementation consists of the following:

  A. The definitions.

     The Unsatisfiable class is defined in GHC.TypeError, in base.
     It consists of the following definitions:

       type Unsatisfiable :: ErrorMessage -> Constraint
       class Unsatisfiable msg where
         unsatisfiableLifted :: a

       unsatisfiable :: forall {rep} (msg :: ErrorMessage) (a :: TYPE rep). Unsatisfiable msg => a
       unsatisfiable = unsatisfiableLifted @msg @((##) -> a) (##)

     The class TyCon as well as the unsatisfiable Id have known-key Names
     in GHC; they are not wired-in.

  B. Unsatisfiable instances.

     The Unsatisfiable typeclass has no instances (see GHC.Tc.Instance.Class.matchGlobalInst).

     Users are prevented from writing instances in GHC.Tc.Validity.check_special_inst_head.
     This is done using the same mechanism as for, say, Coercible or WithDict.

  C. Using [G] Unsatisfiable msg to solve any Wanted.

     In GHC.Tc.Solver.simplifyTopWanteds, after defaulting happens, when an
     implication contains Givens of the form [G] Unsatisfiable msg, and the
     implication supports term-level evidence (as per Note [Coercion evidence only]
     in GHC.Tc.Types.Evidence), we use any such Given to solve all the Wanteds
     in that implication. See GHC.Tc.Solver.useUnsatisfiableGivens.

     The way we construct the evidence terms is slightly complicated by
     Type vs Constraint considerations; see Note [Evidence terms from Unsatisfiable Givens]
     in GHC.Tc.Solver.

     The proposal explains why this happens after defaulting: if there are other
     ways to solve the Wanteds, we would prefer to use that, as that will make
     user programs "as defined as possible".

     Wrinkle [Ambiguity]

       We also use an Unsatisfiable Given to solve Wanteds when performing an
       ambiguity check. See the call to "useUnsatisfiableGivens" in
       GHC.Tc.Solver.simplifyAmbiguityCheck.

       This is, for example, required to typecheck the definition
       of "unsatisfiable" itself:

         unsatisfiable :: forall {rep} (msg :: ErrorMessage) (a :: TYPE rep). Unsatisfiable msg => a

       The ambiguity check on this type signature will produce

         [G] Unsatisfiable msg1, [W] Unsatisfiable msg2

       and we want to ensure the Given solves the Wanted, to accept the definition.

       NB:

         An alternative would be to add a functional dependency on Unsatisfiable:

           class Unsatisfiable msg | -> msg

         Then we would unify msg1 and msg2 in the above constraint solving problem,
         and would be able to solve the Wanted using the Given in the normal way.
         However, adding such a functional dependency solely for this purpose
         could have undesirable consequences. For example, one might have

           [W] Unsatisfiable (Text "msg1"), [W] Unsatisfiable (Text "msg2")

         and W-W fundep interaction would produce the insoluble constraint

           [W] "msg1" ~ "msg2"

         which we definitely wouldn't want to report to the user.

  D. Adding "meth = unsatisfiable @msg" method bindings.

     When a class instance has an "Unsatisfiable msg" constraint in its context,
     and the user has omitted methods, we add method bindings of the form
     "meth = unsatisfiable @msg".
     See GHC.Tc.TyCl.Instance.tcMethods, in particular "tc_default".

     Example:

         class C a where { op :: a -> a }
         instance Unsatisfiable Msg => C [a] where {}

       elaborates to

         instance Unsatisfiable Msg => C [a] where { op = unsatisfiable @Msg }

       due to the (Unsatisfiable Msg) constraint in the instance context.

     We also switch off the "missing methods" warning in this situation.
     See "checkMinimalDefinition" in GHC.Tc.TyCl.Instance.tcMethods.

     Note that we do this even when there is a default method available. This
     ensures we run into the unsatisfiable error message when deferring type
     errors; otherwise we could end up with a runtime loop as seen in #23816.

  E. Switching off functional dependency coverage checks when there is
     an "Unsatisfiable msg" context.

     This is because we want to allow users to rule out certain instances with
     an "unsatisfiable" error, even when that would violate a functional
     dependency. For example:

       class C a b | a -> b
       instance Unsatisfiable (Text "No") => C a b

     See GHC.Tc.Instance.FunDeps.checkInstCoverage.

  F. Error reporting of "Unsatisfiable msg" constraints.

     This is done in GHC.Tc.Errors.reportWanteds: we detect when a constraint
     is of the form "Unsatisfiable msg" and just emit the custom message
     as an error to the user.

     This is the only way that "Unsatisfiable msg" constraints are reported,
     which makes their behaviour much more predictable than TypeError.
-}


--------------------------------------------
--      Reporters
--------------------------------------------

type Reporter
  = SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM ()
type ReporterSpec
  = ( String                      -- Name
    , ErrorItem -> Pred -> Bool  -- Pick these ones
    , Bool                        -- True <=> suppress subsequent reporters
    , Reporter)                   -- The reporter itself

mkSkolReporter :: Reporter
-- Suppress duplicates with either the same LHS, or same location
-- Pre-condition: all items are equalities
mkSkolReporter :: Reporter
mkSkolReporter SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = (NonEmpty ErrorItem -> TcM ()) -> [NonEmpty ErrorItem] -> TcM ()
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ ((SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
reportGroup SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr SolverReportErrCtxt
ctxt) ([ErrorItem] -> [NonEmpty ErrorItem]
group (NonEmpty ErrorItem -> [ErrorItem]
forall a. NonEmpty a -> [a]
forall (t :: * -> *) a. Foldable t => t a -> [a]
toList NonEmpty ErrorItem
items))
  where
     group :: [ErrorItem] -> [NonEmpty ErrorItem]
group [] = []
     group (ErrorItem
item:[ErrorItem]
items) = (ErrorItem
item ErrorItem -> [ErrorItem] -> NonEmpty ErrorItem
forall a. a -> [a] -> NonEmpty a
:| [ErrorItem]
yeses) NonEmpty ErrorItem -> [NonEmpty ErrorItem] -> [NonEmpty ErrorItem]
forall a. a -> [a] -> [a]
: [ErrorItem] -> [NonEmpty ErrorItem]
group [ErrorItem]
noes
        where
          ([ErrorItem]
yeses, [ErrorItem]
noes) = (ErrorItem -> Bool) -> [ErrorItem] -> ([ErrorItem], [ErrorItem])
forall a. (a -> Bool) -> [a] -> ([a], [a])
partition (ErrorItem -> ErrorItem -> Bool
group_with ErrorItem
item) [ErrorItem]
items

     group_with :: ErrorItem -> ErrorItem -> Bool
group_with ErrorItem
item1 ErrorItem
item2
       | Ordering
EQ <- ErrorItem -> ErrorItem -> Ordering
cmp_loc ErrorItem
item1 ErrorItem
item2 = Bool
True
       | ErrorItem -> ErrorItem -> Bool
eq_lhs_type   ErrorItem
item1 ErrorItem
item2 = Bool
True
       | Bool
otherwise                 = Bool
False

reportHoles :: [ErrorItem]  -- other (tidied) constraints
            -> SolverReportErrCtxt -> [Hole] -> TcM ()
reportHoles :: [ErrorItem] -> SolverReportErrCtxt -> [Hole] -> TcM ()
reportHoles [ErrorItem]
tidy_items SolverReportErrCtxt
ctxt [Hole]
holes
  = do
      diag_opts <- DynFlags -> DiagOpts
initDiagOpts (DynFlags -> DiagOpts)
-> IOEnv (Env TcGblEnv TcLclEnv) DynFlags
-> IOEnv (Env TcGblEnv TcLclEnv) DiagOpts
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> IOEnv (Env TcGblEnv TcLclEnv) DynFlags
forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
      let severity = DiagOpts -> DiagnosticReason -> Severity
diagReasonSeverity DiagOpts
diag_opts (SolverReportErrCtxt -> DiagnosticReason
cec_type_holes SolverReportErrCtxt
ctxt)
          holes'   = (Hole -> Bool) -> [Hole] -> [Hole]
forall a. (a -> Bool) -> [a] -> [a]
filter (Severity -> Hole -> Bool
keepThisHole Severity
severity) [Hole]
holes
      -- Zonk and tidy all the TcLclEnvs before calling `mkHoleError`
      -- because otherwise types will be zonked and tidied many times over.
      (tidy_env', lcl_name_cache) <- liftZonkM $
        zonkTidyTcLclEnvs (cec_tidy ctxt) (map (ctl_env . hole_loc) holes')
      let ctxt' = SolverReportErrCtxt
ctxt { cec_tidy = tidy_env' }
      forM_ holes' $ \Hole
hole -> do { msg <- NameEnv Type
-> [ErrorItem]
-> SolverReportErrCtxt
-> Hole
-> TcM (MsgEnvelope TcRnMessage)
mkHoleError NameEnv Type
lcl_name_cache [ErrorItem]
tidy_items SolverReportErrCtxt
ctxt' Hole
hole
                                 ; reportDiagnostic msg }

keepThisHole :: Severity -> Hole -> Bool
-- See Note [Skip type holes rapidly]
keepThisHole :: Severity -> Hole -> Bool
keepThisHole Severity
sev Hole
hole
  = case Hole -> HoleSort
hole_sort Hole
hole of
       ExprHole {}    -> Bool
True
       HoleSort
TypeHole       -> Bool
keep_type_hole
       HoleSort
ConstraintHole -> Bool
keep_type_hole
  where
    keep_type_hole :: Bool
keep_type_hole = case Severity
sev of
                         Severity
SevIgnore -> Bool
False
                         Severity
_         -> Bool
True

-- | zonkTidyTcLclEnvs takes a bunch of 'CtLocEnv's, each from a Hole.
-- It returns a ('Name' :-> 'Type') mapping which gives the zonked, tidied
-- type for each Id in any of the binder stacks in the  'CtLocEnv's.
-- Since there is a huge overlap between these stacks, is is much,
-- much faster to do them all at once, avoiding duplication.
zonkTidyTcLclEnvs :: TidyEnv -> [CtLocEnv] -> ZonkM (TidyEnv, NameEnv Type)
zonkTidyTcLclEnvs :: TidyEnv -> [CtLocEnv] -> ZonkM (TidyEnv, NameEnv Type)
zonkTidyTcLclEnvs TidyEnv
tidy_env [CtLocEnv]
lcls = ((TidyEnv, NameEnv Type)
 -> TcBinder -> ZonkM (TidyEnv, NameEnv Type))
-> (TidyEnv, NameEnv Type)
-> [TcBinder]
-> ZonkM (TidyEnv, NameEnv Type)
forall (t :: * -> *) (m :: * -> *) b a.
(Foldable t, Monad m) =>
(b -> a -> m b) -> b -> t a -> m b
foldM (TidyEnv, NameEnv Type)
-> TcBinder -> ZonkM (TidyEnv, NameEnv Type)
go (TidyEnv
tidy_env, NameEnv Type
forall a. NameEnv a
emptyNameEnv) ((CtLocEnv -> [TcBinder]) -> [CtLocEnv] -> [TcBinder]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap CtLocEnv -> [TcBinder]
ctl_bndrs [CtLocEnv]
lcls)
  where
    go :: (TidyEnv, NameEnv Type)
-> TcBinder -> ZonkM (TidyEnv, NameEnv Type)
go (TidyEnv, NameEnv Type)
envs TcBinder
tc_bndr = case TcBinder
tc_bndr of
          TcTvBndr {} -> (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
forall a. a -> ZonkM a
forall (m :: * -> *) a. Monad m => a -> m a
return (TidyEnv, NameEnv Type)
envs
          TcIdBndr TcId
id TopLevelFlag
_top_lvl -> Name
-> Type -> (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
go_one (TcId -> Name
idName TcId
id) (TcId -> Type
idType TcId
id) (TidyEnv, NameEnv Type)
envs
          TcIdBndr_ExpType Name
name ExpType
et TopLevelFlag
_top_lvl ->
            do { mb_ty <- IO (Maybe Type) -> ZonkM (Maybe Type)
forall a. IO a -> ZonkM a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO (Maybe Type) -> ZonkM (Maybe Type))
-> IO (Maybe Type) -> ZonkM (Maybe Type)
forall a b. (a -> b) -> a -> b
$ ExpType -> IO (Maybe Type)
forall (m :: * -> *). MonadIO m => ExpType -> m (Maybe Type)
readExpType_maybe ExpType
et
                   -- et really should be filled in by now. But there's a chance
                   -- it hasn't, if, say, we're reporting a kind error en route to
                   -- checking a term. See test indexed-types/should_fail/T8129
                   -- Or we are reporting errors from the ambiguity check on
                   -- a local type signature
               ; case mb_ty of
                   Just Type
ty -> Name
-> Type -> (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
go_one Name
name Type
ty (TidyEnv, NameEnv Type)
envs
                   Maybe Type
Nothing -> (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
forall a. a -> ZonkM a
forall (m :: * -> *) a. Monad m => a -> m a
return (TidyEnv, NameEnv Type)
envs
               }
    go_one :: Name
-> Type -> (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
go_one Name
name Type
ty (TidyEnv
tidy_env, NameEnv Type
name_env) = do
            if Name
name Name -> NameEnv Type -> Bool
forall a. Name -> NameEnv a -> Bool
`elemNameEnv` NameEnv Type
name_env
              then (TidyEnv, NameEnv Type) -> ZonkM (TidyEnv, NameEnv Type)
forall a. a -> ZonkM a
forall (m :: * -> *) a. Monad m => a -> m a
return (TidyEnv
tidy_env, NameEnv Type
name_env)
              else do
                (tidy_env', tidy_ty) <- TidyEnv -> Type -> ZonkM (TidyEnv, Type)
zonkTidyTcType TidyEnv
tidy_env Type
ty
                return (tidy_env',  extendNameEnv name_env name tidy_ty)

reportNotConcreteErrs :: SolverReportErrCtxt -> [NotConcreteError] -> TcM ()
reportNotConcreteErrs :: SolverReportErrCtxt -> [NotConcreteError] -> TcM ()
reportNotConcreteErrs SolverReportErrCtxt
_ [] = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()
reportNotConcreteErrs SolverReportErrCtxt
ctxt errs :: [NotConcreteError]
errs@(NotConcreteError
err0:[NotConcreteError]
_)
  = do { msg <- CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport (CtLoc -> CtLocEnv
ctLocEnv (NotConcreteError -> CtLoc
nce_loc NotConcreteError
err0)) TcRnMessage
diag (SolverReportErrCtxt -> Maybe SolverReportErrCtxt
forall a. a -> Maybe a
Just SolverReportErrCtxt
ctxt) []
       ; reportDiagnostic msg }

  where

    frr_origins :: [FixedRuntimeRepErrorInfo]
frr_origins = [NotConcreteError] -> [FixedRuntimeRepErrorInfo]
acc_errors [NotConcreteError]
errs
    diag :: TcRnMessage
diag = SolverReportWithCtxt -> DiagnosticReason -> TcRnMessage
TcRnSolverReport
             (SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt ([FixedRuntimeRepErrorInfo] -> TcSolverReportMsg
FixedRuntimeRepError [FixedRuntimeRepErrorInfo]
frr_origins))
             DiagnosticReason
ErrorWithoutFlag

    -- Accumulate the different kind of errors arising from syntactic equality.
    -- (Only SynEq_FRR origin for the moment.)
    acc_errors :: [NotConcreteError] -> [FixedRuntimeRepErrorInfo]
acc_errors = [FixedRuntimeRepErrorInfo]
-> [NotConcreteError] -> [FixedRuntimeRepErrorInfo]
go []
      where
        go :: [FixedRuntimeRepErrorInfo]
-> [NotConcreteError] -> [FixedRuntimeRepErrorInfo]
go [FixedRuntimeRepErrorInfo]
frr_errs [] = [FixedRuntimeRepErrorInfo]
frr_errs
        go [FixedRuntimeRepErrorInfo]
frr_errs (NotConcreteError
err:[NotConcreteError]
errs)
          | [FixedRuntimeRepErrorInfo]
frr_errs <- [FixedRuntimeRepErrorInfo]
-> [NotConcreteError] -> [FixedRuntimeRepErrorInfo]
go [FixedRuntimeRepErrorInfo]
frr_errs [NotConcreteError]
errs
          = case NotConcreteError
err of
              NCE_FRR
                { nce_frr_origin :: NotConcreteError -> FixedRuntimeRepOrigin
nce_frr_origin = FixedRuntimeRepOrigin
frr_orig
                , nce_reasons :: NotConcreteError -> NonEmpty NotConcreteReason
nce_reasons = NonEmpty NotConcreteReason
_not_conc } ->
                FRR_Info
                  { frr_info_origin :: FixedRuntimeRepOrigin
frr_info_origin       = FixedRuntimeRepOrigin
frr_orig
                  , frr_info_not_concrete :: Maybe (TcId, Type)
frr_info_not_concrete = Maybe (TcId, Type)
forall a. Maybe a
Nothing }
                FixedRuntimeRepErrorInfo
-> [FixedRuntimeRepErrorInfo] -> [FixedRuntimeRepErrorInfo]
forall a. a -> [a] -> [a]
: [FixedRuntimeRepErrorInfo]
frr_errs

{- Note [Skip type holes rapidly]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we have module with a /lot/ of partial type signatures, and we
compile it while suppressing partial-type-signature warnings.  Then
we don't want to spend ages constructing error messages and lists of
relevant bindings that we never display! This happened in #14766, in
which partial type signatures in a Happy-generated parser cause a huge
increase in compile time.

The function ignoreThisHole short-circuits the error/warning generation
machinery, in cases where it is definitely going to be a no-op.
-}

mkUserTypeErrorReporter :: Reporter
mkUserTypeErrorReporter :: Reporter
mkUserTypeErrorReporter SolverReportErrCtxt
ctxt
  = (ErrorItem -> TcM ()) -> NonEmpty ErrorItem -> TcM ()
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ ((ErrorItem -> TcM ()) -> NonEmpty ErrorItem -> TcM ())
-> (ErrorItem -> TcM ()) -> NonEmpty ErrorItem -> TcM ()
forall a b. (a -> b) -> a -> b
$ \ErrorItem
item -> do { let err :: SolverReport
err = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important SolverReportErrCtxt
ctxt (TcSolverReportMsg -> SolverReport)
-> TcSolverReportMsg -> SolverReport
forall a b. (a -> b) -> a -> b
$ ErrorItem -> TcSolverReportMsg
mkUserTypeError ErrorItem
item
                        ; SolverReportErrCtxt -> NonEmpty ErrorItem -> SolverReport -> TcM ()
maybeReportError SolverReportErrCtxt
ctxt (ErrorItem
item ErrorItem -> [ErrorItem] -> NonEmpty ErrorItem
forall a. a -> [a] -> NonEmpty a
:| []) SolverReport
err
                        ; SolverReportErrCtxt -> SolverReport -> ErrorItem -> TcM ()
addDeferredBinding SolverReportErrCtxt
ctxt SolverReport
err ErrorItem
item }

mkUserTypeError :: ErrorItem -> TcSolverReportMsg
mkUserTypeError :: ErrorItem -> TcSolverReportMsg
mkUserTypeError ErrorItem
item
  | Just Type
msg <- Type -> Maybe Type
getUserTypeErrorMsg Type
pty
  = Type -> TcSolverReportMsg
UserTypeError Type
msg
  | Just Type
msg <- Type -> Maybe Type
isUnsatisfiableCt_maybe Type
pty
  = Type -> TcSolverReportMsg
UnsatisfiableError Type
msg
  | Bool
otherwise
  = String -> SDoc -> TcSolverReportMsg
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"mkUserTypeError" (ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr ErrorItem
item)
  where
    pty :: Type
pty = ErrorItem -> Type
errorItemPred ErrorItem
item

mkGivenErrorReporter :: Reporter
-- See Note [Given errors]
mkGivenErrorReporter :: Reporter
mkGivenErrorReporter SolverReportErrCtxt
ctxt (ErrorItem
item:|[ErrorItem]
_)
  = do { (ctxt, relevant_binds, item) <- Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
True SolverReportErrCtxt
ctxt ErrorItem
item
       ; let (implic:_) = cec_encl ctxt
                 -- Always non-empty when mkGivenErrorReporter is called
             loc'  = CtLoc -> CtLocEnv -> CtLoc
setCtLocEnv (ErrorItem -> CtLoc
ei_loc ErrorItem
item) (Implication -> CtLocEnv
ic_env Implication
implic)
             item' = ErrorItem
item { ei_loc = loc' }
                   -- For given constraints we overwrite the env (and hence src-loc)
                   -- with one from the immediately-enclosing implication.
                   -- See Note [Inaccessible code]
       ; eq_err_msg <- mkEqErr_help ctxt item' ty1 ty2
       ; let supplementary = [ RelevantBindings -> SolverReportSupplementary
SupplementaryBindings RelevantBindings
relevant_binds ]
             msg = Implication -> SolverReportWithCtxt -> TcRnMessage
TcRnInaccessibleCode Implication
implic (SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt TcSolverReportMsg
eq_err_msg)
       ; msg <- mkErrorReport (ctLocEnv loc') msg (Just ctxt) supplementary
       ; reportDiagnostic msg }
  where
    (Type
ty1, Type
ty2)   = Type -> (Type, Type)
getEqPredTys (ErrorItem -> Type
errorItemPred ErrorItem
item)

ignoreErrorReporter :: Reporter
-- Discard Given errors that don't come from
-- a pattern match; maybe we should warn instead?
ignoreErrorReporter :: Reporter
ignoreErrorReporter SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = do { String -> SDoc -> TcM ()
traceTc String
"mkGivenErrorReporter no" (NonEmpty ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr NonEmpty ErrorItem
items SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [Implication] -> SDoc
forall a. Outputable a => a -> SDoc
ppr (SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt))
       ; () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return () }


{- Note [Given errors]
~~~~~~~~~~~~~~~~~~~~~~
Given constraints represent things for which we have (or will have)
evidence, so they aren't errors.  But if a Given constraint is
insoluble, this code is inaccessible, and we might want to at least
warn about that.  A classic case is

   data T a where
     T1 :: T Int
     T2 :: T a
     T3 :: T Bool

   f :: T Int -> Bool
   f T1 = ...
   f T2 = ...
   f T3 = ...  -- We want to report this case as inaccessible

We'd like to point out that the T3 match is inaccessible. It
will have a Given constraint [G] Int ~ Bool.

But we don't want to report ALL insoluble Given constraints.  See Trac
#12466 for a long discussion.  For example, if we aren't careful
we'll complain about
   f :: ((Int ~ Bool) => a -> a) -> Int
which arguably is OK.  It's more debatable for
   g :: (Int ~ Bool) => Int -> Int
but it's tricky to distinguish these cases so we don't report
either.

The bottom line is this: has_gadt_match looks for an enclosing
pattern match which binds some equality constraints.  If we
find one, we report the insoluble Given.
-}

mkGroupReporter :: (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
                             -- Make error message for a group
                -> Reporter  -- Deal with lots of constraints
-- Group together errors from same location,
-- and report only the first (to avoid a cascade)
mkGroupReporter :: (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
mkGroupReporter SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mk_err SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = (NonEmpty ErrorItem -> TcM ()) -> [NonEmpty ErrorItem] -> TcM ()
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ ((SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
reportGroup SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mk_err SolverReportErrCtxt
ctxt) ((ErrorItem -> ErrorItem -> Ordering)
-> [ErrorItem] -> [NonEmpty ErrorItem]
forall a. (a -> a -> Ordering) -> [a] -> [NonEmpty a]
equivClasses ErrorItem -> ErrorItem -> Ordering
cmp_loc (NonEmpty ErrorItem -> [ErrorItem]
forall a. NonEmpty a -> [a]
forall (t :: * -> *) a. Foldable t => t a -> [a]
toList NonEmpty ErrorItem
items))

eq_lhs_type :: ErrorItem -> ErrorItem -> Bool
eq_lhs_type :: ErrorItem -> ErrorItem -> Bool
eq_lhs_type ErrorItem
item1 ErrorItem
item2
  = case (Type -> Pred
classifyPredType (ErrorItem -> Type
errorItemPred ErrorItem
item1), Type -> Pred
classifyPredType (ErrorItem -> Type
errorItemPred ErrorItem
item2)) of
       (EqPred EqRel
eq_rel1 Type
ty1 Type
_, EqPred EqRel
eq_rel2 Type
ty2 Type
_) ->
         (EqRel
eq_rel1 EqRel -> EqRel -> Bool
forall a. Eq a => a -> a -> Bool
== EqRel
eq_rel2) Bool -> Bool -> Bool
&& (Type
ty1 Type -> Type -> Bool
`eqType` Type
ty2)
       (Pred, Pred)
_ -> String -> SDoc -> Bool
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"mkSkolReporter" (ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr ErrorItem
item1 SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr ErrorItem
item2)

cmp_loc :: ErrorItem -> ErrorItem -> Ordering
cmp_loc :: ErrorItem -> ErrorItem -> Ordering
cmp_loc ErrorItem
item1 ErrorItem
item2 = ErrorItem -> RealSrcLoc
get ErrorItem
item1 RealSrcLoc -> RealSrcLoc -> Ordering
forall a. Ord a => a -> a -> Ordering
`compare` ErrorItem -> RealSrcLoc
get ErrorItem
item2
  where
    get :: ErrorItem -> RealSrcLoc
get ErrorItem
ei = RealSrcSpan -> RealSrcLoc
realSrcSpanStart (CtLoc -> RealSrcSpan
ctLocSpan (ErrorItem -> CtLoc
errorItemCtLoc ErrorItem
ei))
             -- Reduce duplication by reporting only one error from each
             -- /starting/ location even if the end location differs

reportGroup :: (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport) -> Reporter
reportGroup :: (SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport)
-> Reporter
reportGroup SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mk_err SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = do { err <- SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mk_err SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
       ; traceTc "About to maybeReportErr" $
         vcat [ text "Constraint:"             <+> ppr items
              , text "cec_suppress ="          <+> ppr (cec_suppress ctxt)
              , text "cec_defer_type_errors =" <+> ppr (cec_defer_type_errors ctxt) ]
       ; maybeReportError ctxt items err
           -- But see Note [Always warn with -fdefer-type-errors]
       ; traceTc "reportGroup" (ppr items)
       ; mapM_ (addDeferredBinding ctxt err) items }
           -- Add deferred bindings for all
           -- Redundant if we are going to abort compilation,
           -- but that's hard to know for sure, and if we don't
           -- abort, we need bindings for all (e.g. #12156)

-- See Note [No deferring for multiplicity errors]
nonDeferrableOrigin :: CtOrigin -> Bool
nonDeferrableOrigin :: CtOrigin -> Bool
nonDeferrableOrigin (NonLinearPatternOrigin {}) = Bool
True
nonDeferrableOrigin (UsageEnvironmentOf {}) = Bool
True
nonDeferrableOrigin (FRROrigin {})          = Bool
True
nonDeferrableOrigin CtOrigin
_                       = Bool
False

maybeReportError :: SolverReportErrCtxt
                 -> NonEmpty ErrorItem     -- items covered by the Report
                 -> SolverReport -> TcM ()
maybeReportError :: SolverReportErrCtxt -> NonEmpty ErrorItem -> SolverReport -> TcM ()
maybeReportError SolverReportErrCtxt
ctxt items :: NonEmpty ErrorItem
items@(ErrorItem
item1:|[ErrorItem]
_) (SolverReport { sr_important_msg :: SolverReport -> SolverReportWithCtxt
sr_important_msg = SolverReportWithCtxt
important
                                                     , sr_supplementary :: SolverReport -> [SolverReportSupplementary]
sr_supplementary = [SolverReportSupplementary]
supp })
  = Bool -> TcM () -> TcM ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
unless (SolverReportErrCtxt -> Bool
cec_suppress SolverReportErrCtxt
ctxt  -- Some worse error has occurred, so suppress this diagnostic
         Bool -> Bool -> Bool
|| (ErrorItem -> Bool) -> NonEmpty ErrorItem -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all ErrorItem -> Bool
ei_suppress NonEmpty ErrorItem
items) (TcM () -> TcM ()) -> TcM () -> TcM ()
forall a b. (a -> b) -> a -> b
$
                           -- if they're all to be suppressed, report nothing
                           -- if at least one is not suppressed, do report:
                           -- the function that generates the error message
                           -- should look for an unsuppressed error item
    do let reason :: DiagnosticReason
reason | (ErrorItem -> Bool) -> NonEmpty ErrorItem -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (CtOrigin -> Bool
nonDeferrableOrigin (CtOrigin -> Bool) -> (ErrorItem -> CtOrigin) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> CtOrigin
errorItemOrigin) NonEmpty ErrorItem
items = DiagnosticReason
ErrorWithoutFlag
                  | Bool
otherwise                                         = SolverReportErrCtxt -> DiagnosticReason
cec_defer_type_errors SolverReportErrCtxt
ctxt
                  -- See Note [No deferring for multiplicity errors]
           diag :: TcRnMessage
diag = SolverReportWithCtxt -> DiagnosticReason -> TcRnMessage
TcRnSolverReport SolverReportWithCtxt
important DiagnosticReason
reason
       msg <- CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport (CtLoc -> CtLocEnv
ctLocEnv (ErrorItem -> CtLoc
errorItemCtLoc ErrorItem
item1)) TcRnMessage
diag (SolverReportErrCtxt -> Maybe SolverReportErrCtxt
forall a. a -> Maybe a
Just SolverReportErrCtxt
ctxt) [SolverReportSupplementary]
supp
       reportDiagnostic msg

addDeferredBinding :: SolverReportErrCtxt -> SolverReport -> ErrorItem -> TcM ()
-- See Note [Deferring coercion errors to runtime]
addDeferredBinding :: SolverReportErrCtxt -> SolverReport -> ErrorItem -> TcM ()
addDeferredBinding SolverReportErrCtxt
ctxt SolverReport
err (EI { ei_evdest :: ErrorItem -> Maybe TcEvDest
ei_evdest = Just TcEvDest
dest, ei_pred :: ErrorItem -> Type
ei_pred = Type
item_ty
                                , ei_loc :: ErrorItem -> CtLoc
ei_loc = CtLoc
loc })
     -- if evdest is Just, then the constraint was from a wanted
  | SolverReportErrCtxt -> Bool
deferringAnyBindings SolverReportErrCtxt
ctxt
  = do { err_tm <- SolverReportErrCtxt -> CtLoc -> Type -> SolverReport -> TcM EvTerm
mkErrorTerm SolverReportErrCtxt
ctxt CtLoc
loc Type
item_ty SolverReport
err
       ; let ev_binds_var = SolverReportErrCtxt -> EvBindsVar
cec_binds SolverReportErrCtxt
ctxt

       ; case dest of
           EvVarDest TcId
evar
             -> EvBindsVar -> EvBind -> TcM ()
addTcEvBind EvBindsVar
ev_binds_var (EvBind -> TcM ()) -> EvBind -> TcM ()
forall a b. (a -> b) -> a -> b
$ TcId -> Bool -> EvTerm -> EvBind
mkWantedEvBind TcId
evar Bool
True EvTerm
err_tm
           HoleDest CoercionHole
hole
             -> do { -- See Note [Deferred errors for coercion holes]
                     let co_var :: TcId
co_var = CoercionHole -> TcId
coHoleCoVar CoercionHole
hole
                   ; EvBindsVar -> EvBind -> TcM ()
addTcEvBind EvBindsVar
ev_binds_var (EvBind -> TcM ()) -> EvBind -> TcM ()
forall a b. (a -> b) -> a -> b
$ TcId -> Bool -> EvTerm -> EvBind
mkWantedEvBind TcId
co_var Bool
True EvTerm
err_tm
                   ; CoercionHole -> TcCoercionN -> TcM ()
fillCoercionHole CoercionHole
hole (TcId -> TcCoercionN
mkCoVarCo TcId
co_var) } }
addDeferredBinding SolverReportErrCtxt
_ SolverReport
_ ErrorItem
_ = () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ()    -- Do not set any evidence for Given

mkErrorTerm :: SolverReportErrCtxt -> CtLoc -> Type  -- of the error term
            -> SolverReport -> TcM EvTerm
mkErrorTerm :: SolverReportErrCtxt -> CtLoc -> Type -> SolverReport -> TcM EvTerm
mkErrorTerm SolverReportErrCtxt
ctxt CtLoc
ct_loc Type
ty (SolverReport { sr_important_msg :: SolverReport -> SolverReportWithCtxt
sr_important_msg = SolverReportWithCtxt
important, sr_supplementary :: SolverReport -> [SolverReportSupplementary]
sr_supplementary = [SolverReportSupplementary]
supp })
  = do { msg <- CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport
                  (CtLoc -> CtLocEnv
ctLocEnv CtLoc
ct_loc)
                  (SolverReportWithCtxt -> DiagnosticReason -> TcRnMessage
TcRnSolverReport SolverReportWithCtxt
important DiagnosticReason
ErrorWithoutFlag) (SolverReportErrCtxt -> Maybe SolverReportErrCtxt
forall a. a -> Maybe a
Just SolverReportErrCtxt
ctxt) [SolverReportSupplementary]
supp
         -- This will be reported at runtime, so we always want "error:" in the report, never "warning:"
       ; dflags <- getDynFlags
       ; let err_msg = DiagnosticOpts TcRnMessage -> MsgEnvelope TcRnMessage -> SDoc
forall e. Diagnostic e => DiagnosticOpts e -> MsgEnvelope e -> SDoc
pprLocMsgEnvelope (DynFlags -> DiagnosticOpts TcRnMessage
initTcMessageOpts DynFlags
dflags) MsgEnvelope TcRnMessage
msg
             err_str = DynFlags -> SDoc -> String
showSDoc DynFlags
dflags (SDoc -> String) -> SDoc -> String
forall a b. (a -> b) -> a -> b
$
                       SDoc
err_msg SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"(deferred type error)"

       ; return $ evDelayedError ty err_str }

tryReporters :: SolverReportErrCtxt -> [ReporterSpec] -> [ErrorItem] -> TcM (SolverReportErrCtxt, [ErrorItem])
-- Use the first reporter in the list whose predicate says True
tryReporters :: SolverReportErrCtxt
-> [ReporterSpec]
-> [ErrorItem]
-> TcM (SolverReportErrCtxt, [ErrorItem])
tryReporters SolverReportErrCtxt
ctxt [ReporterSpec]
reporters [ErrorItem]
items
  = do { let ([ErrorItem]
vis_items, [ErrorItem]
invis_items)
               = (ErrorItem -> Bool) -> [ErrorItem] -> ([ErrorItem], [ErrorItem])
forall a. (a -> Bool) -> [a] -> ([a], [a])
partition (CtOrigin -> Bool
isVisibleOrigin (CtOrigin -> Bool) -> (ErrorItem -> CtOrigin) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> CtOrigin
errorItemOrigin) [ErrorItem]
items
       ; String -> SDoc -> TcM ()
traceTc String
"tryReporters {" ([ErrorItem] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [ErrorItem]
vis_items SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ [ErrorItem] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [ErrorItem]
invis_items)
       ; (ctxt', items') <- SolverReportErrCtxt
-> [ReporterSpec]
-> [ErrorItem]
-> [ErrorItem]
-> TcM (SolverReportErrCtxt, [ErrorItem])
go SolverReportErrCtxt
ctxt [ReporterSpec]
reporters [ErrorItem]
vis_items [ErrorItem]
invis_items
       ; traceTc "tryReporters }" (ppr items')
       ; return (ctxt', items') }
  where
    go :: SolverReportErrCtxt
-> [ReporterSpec]
-> [ErrorItem]
-> [ErrorItem]
-> TcM (SolverReportErrCtxt, [ErrorItem])
go SolverReportErrCtxt
ctxt [] [ErrorItem]
vis_items [ErrorItem]
invis_items
      = (SolverReportErrCtxt, [ErrorItem])
-> TcM (SolverReportErrCtxt, [ErrorItem])
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (SolverReportErrCtxt
ctxt, [ErrorItem]
vis_items [ErrorItem] -> [ErrorItem] -> [ErrorItem]
forall a. [a] -> [a] -> [a]
++ [ErrorItem]
invis_items)

    go SolverReportErrCtxt
ctxt (ReporterSpec
r : [ReporterSpec]
rs) [ErrorItem]
vis_items [ErrorItem]
invis_items
       -- always look at *visible* Origins before invisible ones
       -- this is the whole point of isVisibleOrigin
      = do { (ctxt', vis_items') <- SolverReportErrCtxt
-> ReporterSpec
-> [ErrorItem]
-> TcM (SolverReportErrCtxt, [ErrorItem])
tryReporter SolverReportErrCtxt
ctxt ReporterSpec
r [ErrorItem]
vis_items
           ; (ctxt'', invis_items') <- tryReporter ctxt' r invis_items
           ; go ctxt'' rs vis_items' invis_items' }
                -- Carry on with the rest, because we must make
                -- deferred bindings for them if we have -fdefer-type-errors
                -- But suppress their error messages

tryReporter :: SolverReportErrCtxt -> ReporterSpec -> [ErrorItem] -> TcM (SolverReportErrCtxt, [ErrorItem])
tryReporter :: SolverReportErrCtxt
-> ReporterSpec
-> [ErrorItem]
-> TcM (SolverReportErrCtxt, [ErrorItem])
tryReporter SolverReportErrCtxt
ctxt (String
str, ErrorItem -> Pred -> Bool
keep_me,  Bool
suppress_after, Reporter
reporter) [ErrorItem]
items = case [ErrorItem] -> Maybe (NonEmpty ErrorItem)
forall a. [a] -> Maybe (NonEmpty a)
nonEmpty [ErrorItem]
yeses of
    Maybe (NonEmpty ErrorItem)
Nothing -> (SolverReportErrCtxt, [ErrorItem])
-> TcM (SolverReportErrCtxt, [ErrorItem])
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (f :: * -> *) a. Applicative f => a -> f a
pure (SolverReportErrCtxt
ctxt, [ErrorItem]
items)
    Just NonEmpty ErrorItem
yeses -> do
       { String -> SDoc -> TcM ()
traceTc String
"tryReporter{ " (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
str SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> NonEmpty ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr NonEmpty ErrorItem
yeses)
       ; (_, no_errs) <- TcM () -> TcRn ((), Bool)
forall a. TcRn a -> TcRn (a, Bool)
askNoErrs (Reporter
reporter SolverReportErrCtxt
ctxt NonEmpty ErrorItem
yeses)
       ; let suppress_now   = Bool -> Bool
not Bool
no_errs Bool -> Bool -> Bool
&& Bool
suppress_after
                            -- See Note [Suppressing error messages]
             ctxt' = SolverReportErrCtxt
ctxt { cec_suppress = suppress_now || cec_suppress ctxt }
       ; traceTc "tryReporter end }" (text str <+> ppr (cec_suppress ctxt) <+> ppr suppress_after)
       ; return (ctxt', nos) }
  where
    ([ErrorItem]
yeses, [ErrorItem]
nos) = (ErrorItem -> Bool) -> [ErrorItem] -> ([ErrorItem], [ErrorItem])
forall a. (a -> Bool) -> [a] -> ([a], [a])
partition ErrorItem -> Bool
keep [ErrorItem]
items
    keep :: ErrorItem -> Bool
keep ErrorItem
item = ErrorItem -> Pred -> Bool
keep_me ErrorItem
item (Type -> Pred
classifyPredType (ErrorItem -> Type
errorItemPred ErrorItem
item))

-- | Wrap an input 'TcRnMessage' with additional contextual information,
-- such as relevant bindings or valid hole fits.
mkErrorReport :: CtLocEnv
              -> TcRnMessage
                  -- ^ The main payload of the message.
              -> Maybe SolverReportErrCtxt
                  -- ^ The context to add, after the main diagnostic
                  -- but before the supplementary information.
                  -- Nothing <=> don't add any context.
              -> [SolverReportSupplementary]
                  -- ^ Supplementary information, to be added at the end of the message.
              -> TcM (MsgEnvelope TcRnMessage)
mkErrorReport :: CtLocEnv
-> TcRnMessage
-> Maybe SolverReportErrCtxt
-> [SolverReportSupplementary]
-> TcM (MsgEnvelope TcRnMessage)
mkErrorReport CtLocEnv
tcl_env TcRnMessage
msg Maybe SolverReportErrCtxt
mb_ctxt [SolverReportSupplementary]
supplementary
  = do { mb_context <- (SolverReportErrCtxt -> IOEnv (Env TcGblEnv TcLclEnv) SDoc)
-> Maybe SolverReportErrCtxt
-> IOEnv (Env TcGblEnv TcLclEnv) (Maybe SDoc)
forall (t :: * -> *) (f :: * -> *) a b.
(Traversable t, Applicative f) =>
(a -> f b) -> t a -> f (t b)
forall (f :: * -> *) a b.
Applicative f =>
(a -> f b) -> Maybe a -> f (Maybe b)
traverse (\ SolverReportErrCtxt
ctxt -> TidyEnv -> [ErrCtxt] -> IOEnv (Env TcGblEnv TcLclEnv) SDoc
mkErrInfo (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt) (CtLocEnv -> [ErrCtxt]
ctl_ctxt CtLocEnv
tcl_env)) Maybe SolverReportErrCtxt
mb_ctxt
       ; unit_state <- hsc_units <$> getTopEnv
       ; hfdc <- getHoleFitDispConfig
       ; let
           err_info =
             SDoc -> SDoc -> ErrInfo
ErrInfo
               (SDoc -> Maybe SDoc -> SDoc
forall a. a -> Maybe a -> a
fromMaybe SDoc
forall doc. IsOutput doc => doc
empty Maybe SDoc
mb_context)
               ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat ([SDoc] -> SDoc) -> [SDoc] -> SDoc
forall a b. (a -> b) -> a -> b
$ (SolverReportSupplementary -> SDoc)
-> [SolverReportSupplementary] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (HoleFitDispConfig -> SolverReportSupplementary -> SDoc
pprSolverReportSupplementary HoleFitDispConfig
hfdc) [SolverReportSupplementary]
supplementary)
       ; let detailed_msg = ErrInfo -> TcRnMessage -> TcRnMessageDetailed
mkDetailedMessage ErrInfo
err_info TcRnMessage
msg
       ; mkTcRnMessage
           (RealSrcSpan (ctl_loc tcl_env) Strict.Nothing)
           (TcRnMessageWithInfo unit_state $ detailed_msg) }



-- | Pretty-print supplementary information, to add to an error report.
pprSolverReportSupplementary :: HoleFitDispConfig -> SolverReportSupplementary -> SDoc
-- This function should be in "GHC.Tc.Errors.Ppr",
-- but we need it here because 'TcRnMessageDetails' needs an 'SDoc'.
pprSolverReportSupplementary :: HoleFitDispConfig -> SolverReportSupplementary -> SDoc
pprSolverReportSupplementary HoleFitDispConfig
hfdc = \case
  SupplementaryBindings RelevantBindings
binds -> RelevantBindings -> SDoc
pprRelevantBindings RelevantBindings
binds
  SupplementaryHoleFits ValidHoleFits
fits  -> HoleFitDispConfig -> ValidHoleFits -> SDoc
pprValidHoleFits HoleFitDispConfig
hfdc ValidHoleFits
fits
  SupplementaryCts      [(Type, RealSrcSpan)]
cts   -> [(Type, RealSrcSpan)] -> SDoc
pprConstraintsInclude [(Type, RealSrcSpan)]
cts

-- | Display a collection of valid hole fits.
pprValidHoleFits :: HoleFitDispConfig -> ValidHoleFits -> SDoc
-- This function should be in "GHC.Tc.Errors.Ppr",
-- but we need it here because 'TcRnMessageDetails' needs an 'SDoc'.
pprValidHoleFits :: HoleFitDispConfig -> ValidHoleFits -> SDoc
pprValidHoleFits HoleFitDispConfig
hfdc (ValidHoleFits (Fits [HoleFit]
fits Bool
discarded_fits) (Fits [HoleFit]
refs Bool
discarded_refs))
  = SDoc
fits_msg SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ SDoc
refs_msg

  where
    fits_msg, refs_msg, fits_discard_msg, refs_discard_msg :: SDoc
    fits_msg :: SDoc
fits_msg = Bool -> SDoc -> SDoc
forall doc. IsOutput doc => Bool -> doc -> doc
ppUnless ([HoleFit] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [HoleFit]
fits) (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
                    SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Valid hole fits include") Int
2 (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
                    [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat ((HoleFit -> SDoc) -> [HoleFit] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (HoleFitDispConfig -> HoleFit -> SDoc
pprHoleFit HoleFitDispConfig
hfdc) [HoleFit]
fits)
                      SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Bool -> SDoc -> SDoc
forall doc. IsOutput doc => Bool -> doc -> doc
ppWhen  Bool
discarded_fits SDoc
fits_discard_msg
    refs_msg :: SDoc
refs_msg = Bool -> SDoc -> SDoc
forall doc. IsOutput doc => Bool -> doc -> doc
ppUnless ([HoleFit] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [HoleFit]
refs) (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
                  SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Valid refinement hole fits include") Int
2 (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
                  [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat ((HoleFit -> SDoc) -> [HoleFit] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (HoleFitDispConfig -> HoleFit -> SDoc
pprHoleFit HoleFitDispConfig
hfdc) [HoleFit]
refs)
                    SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Bool -> SDoc -> SDoc
forall doc. IsOutput doc => Bool -> doc -> doc
ppWhen Bool
discarded_refs SDoc
refs_discard_msg
    fits_discard_msg :: SDoc
fits_discard_msg =
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"(Some hole fits suppressed;" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+>
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"use -fmax-valid-hole-fits=N" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+>
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"or -fno-max-valid-hole-fits)"
    refs_discard_msg :: SDoc
refs_discard_msg =
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"(Some refinement hole fits suppressed;" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+>
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"use -fmax-refinement-hole-fits=N" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+>
      String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"or -fno-max-refinement-hole-fits)"

-- | Add a "Constraints include..." message.
--
-- See Note [Constraints include ...]
pprConstraintsInclude :: [(PredType, RealSrcSpan)] -> SDoc
-- This function should be in "GHC.Tc.Errors.Ppr",
-- but we need it here because 'TcRnMessageDetails' needs an 'SDoc'.
pprConstraintsInclude :: [(Type, RealSrcSpan)] -> SDoc
pprConstraintsInclude [(Type, RealSrcSpan)]
cts
  = Bool -> SDoc -> SDoc
forall doc. IsOutput doc => Bool -> doc -> doc
ppUnless ([(Type, RealSrcSpan)] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [(Type, RealSrcSpan)]
cts) (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$
     SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"Constraints include")
        Int
2 ([SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat ([SDoc] -> SDoc) -> [SDoc] -> SDoc
forall a b. (a -> b) -> a -> b
$ ((Type, RealSrcSpan) -> SDoc) -> [(Type, RealSrcSpan)] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (Type, RealSrcSpan) -> SDoc
forall {a} {a}. (Outputable a, Outputable a) => (a, a) -> SDoc
pprConstraint [(Type, RealSrcSpan)]
cts)
  where
    pprConstraint :: (a, a) -> SDoc
pprConstraint (a
constraint, a
loc) =
      a -> SDoc
forall a. Outputable a => a -> SDoc
ppr a
constraint SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Int -> SDoc -> SDoc
nest Int
2 (SDoc -> SDoc
forall doc. IsLine doc => doc -> doc
parens (String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"from" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> a -> SDoc
forall a. Outputable a => a -> SDoc
ppr a
loc))

{- Note [Always warn with -fdefer-type-errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When -fdefer-type-errors is on we warn about *all* type errors, even
if cec_suppress is on.  This can lead to a lot more warnings than you
would get errors without -fdefer-type-errors, but if we suppress any of
them you might get a runtime error that wasn't warned about at compile
time.

To be consistent, we should also report multiple warnings from a single
location in mkGroupReporter, when -fdefer-type-errors is on.  But that
is perhaps a bit *over*-consistent!

With #10283, you can now opt out of deferred type error warnings.

Note [No deferring for multiplicity errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As explained in Note [Wrapper returned from tcSubMult] in GHC.Tc.Utils.Unify,
linear types do not support casts and any nontrivial coercion will raise
an error during desugaring.

This means that even if we defer a multiplicity mismatch during typechecking,
the desugarer will refuse to compile anyway. Worse: the error raised
by the desugarer would shadow the type mismatch warnings (#20083).
As a solution, we refuse to defer submultiplicity constraints. Test: T20083.

To determine whether a constraint arose from a submultiplicity check, we
look at the CtOrigin. All calls to tcSubMult use one of two origins,
UsageEnvironmentOf and NonLinearPatternOrigin. Those origins are not
used outside of linear types.

In the future, we should compile 'WpMultCoercion' to a runtime error with
-fdefer-type-errors, but the current implementation does not always
place the wrapper in the right place and the resulting program can fail Lint.
This plan is tracked in #20083.

Note [Deferred errors for coercion holes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we need to defer a type error where the destination for the evidence
is a coercion hole. We can't just put the error in the hole, because we can't
make an erroneous coercion. (Remember that coercions are erased for runtime.)
Instead, we invent a new EvVar, bind it to an error and then make a coercion
from that EvVar, filling the hole with that coercion. Because coercions'
types are unlifted, the error is guaranteed to be hit before we get to the
coercion.

************************************************************************
*                                                                      *
                Irreducible predicate errors
*                                                                      *
************************************************************************
-}

mkIrredErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkIrredErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkIrredErr SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = do { (ctxt, binds, item1) <- Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
True SolverReportErrCtxt
ctxt ErrorItem
item1
       ; let msg = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important SolverReportErrCtxt
ctxt (TcSolverReportMsg -> SolverReport)
-> TcSolverReportMsg -> SolverReport
forall a b. (a -> b) -> a -> b
$ MismatchMsg -> TcSolverReportMsg
mkPlainMismatchMsg (MismatchMsg -> TcSolverReportMsg)
-> MismatchMsg -> TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$
                   [Implication]
-> NonEmpty ErrorItem -> Maybe CND_Extra -> MismatchMsg
CouldNotDeduce (SolverReportErrCtxt -> [Implication]
getUserGivens SolverReportErrCtxt
ctxt) (ErrorItem
item1 ErrorItem -> [ErrorItem] -> NonEmpty ErrorItem
forall a. a -> [a] -> NonEmpty a
:| [ErrorItem]
others) Maybe CND_Extra
forall a. Maybe a
Nothing
       ; return $ add_relevant_bindings binds msg  }
  where
    ErrorItem
item1:|[ErrorItem]
others = (ErrorItem -> Bool) -> NonEmpty ErrorItem -> NonEmpty ErrorItem
forall a. (a -> Bool) -> NonEmpty a -> NonEmpty a
tryFilter (Bool -> Bool
not (Bool -> Bool) -> (ErrorItem -> Bool) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> Bool
ei_suppress) NonEmpty ErrorItem
items

{- Note [Constructing Hole Errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Whether or not 'mkHoleError' returns an error is not influenced by cec_suppress. In other terms,
these "hole" errors are /not/ suppressed by cec_suppress. We want to see them!

There are two cases to consider:

1. For out-of-scope variables we always report an error, unless -fdefer-out-of-scope-variables is on,
   in which case the messages are discarded. See also #12170 and #12406. If deferring, report a warning
   only if -Wout-of-scope-variables is on.

2. For the general case, when -XPartialTypeSignatures is on, warnings (instead of errors) are generated
   for holes in partial type signatures, unless -Wpartial-type-signatures is not on, in which case
   the messages are discarded. If deferring, report a warning only if -Wtyped-holes is on.

The above can be summarised into the following table:

| Hole Type    | Active Flags                                             | Outcome          |
|--------------|----------------------------------------------------------|------------------|
| out-of-scope | None                                                     | Error            |
| out-of-scope | -fdefer-out-of-scope-variables, -Wout-of-scope-variables | Warning          |
| out-of-scope | -fdefer-out-of-scope-variables                           | Ignore (discard) |
| type         | None                                                     | Error            |
| type         | -XPartialTypeSignatures, -Wpartial-type-signatures       | Warning          |
| type         | -XPartialTypeSignatures                                  | Ignore (discard) |
| expression   | None                                                     | Error            |
| expression   | -Wdefer-typed-holes, -Wtyped-holes                       | Warning          |
| expression   | -Wdefer-typed-holes                                      | Ignore (discard) |

See also 'reportUnsolved'.

-}

----------------
-- | Constructs a new hole error, unless this is deferred. See Note [Constructing Hole Errors].
mkHoleError :: NameEnv Type -> [ErrorItem] -> SolverReportErrCtxt -> Hole -> TcM (MsgEnvelope TcRnMessage)
mkHoleError :: NameEnv Type
-> [ErrorItem]
-> SolverReportErrCtxt
-> Hole
-> TcM (MsgEnvelope TcRnMessage)
mkHoleError NameEnv Type
_ [ErrorItem]
_tidy_simples SolverReportErrCtxt
ctxt hole :: Hole
hole@(Hole { hole_occ :: Hole -> RdrName
hole_occ = RdrName
occ, hole_loc :: Hole -> CtLoc
hole_loc = CtLoc
ct_loc })
  | Hole -> Bool
isOutOfScopeHole Hole
hole
  = do { (imp_errs, hints)
           <- LocalRdrEnv
-> WhatLooking -> RdrName -> RnM ([ImportError], [GhcHint])
unknownNameSuggestions (CtLocEnv -> LocalRdrEnv
ctl_rdr CtLocEnv
lcl_env) WhatLooking
WL_Anything RdrName
occ
       ; let
             err    = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt
                    (TcSolverReportMsg -> SolverReportWithCtxt)
-> TcSolverReportMsg -> SolverReportWithCtxt
forall a b. (a -> b) -> a -> b
$ Hole -> HoleError -> TcSolverReportMsg
ReportHoleError Hole
hole
                    (HoleError -> TcSolverReportMsg) -> HoleError -> TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$ [ImportError] -> [GhcHint] -> HoleError
OutOfScopeHole [ImportError]
imp_errs [GhcHint]
hints
             report = SolverReportWithCtxt -> [SolverReportSupplementary] -> SolverReport
SolverReport SolverReportWithCtxt
err []

       ; maybeAddDeferredBindings ctxt hole report
       ; mkErrorReport lcl_env (TcRnSolverReport err (cec_out_of_scope_holes ctxt))
           Nothing []
          -- Pass the value 'Nothing' for the context, as it's generally not helpful
          -- to include the context here.
       }
  where
    lcl_env :: CtLocEnv
lcl_env = CtLoc -> CtLocEnv
ctLocEnv CtLoc
ct_loc

 -- general case: not an out-of-scope error
mkHoleError NameEnv Type
lcl_name_cache [ErrorItem]
tidy_simples SolverReportErrCtxt
ctxt
  hole :: Hole
hole@(Hole { hole_ty :: Hole -> Type
hole_ty = Type
hole_ty
             , hole_sort :: Hole -> HoleSort
hole_sort = HoleSort
sort
             , hole_loc :: Hole -> CtLoc
hole_loc = CtLoc
ct_loc })
  = do { rel_binds
           <- Bool
-> CtLocEnv -> NameEnv Type -> TyCoVarSet -> TcM RelevantBindings
relevant_bindings Bool
False CtLocEnv
lcl_env NameEnv Type
lcl_name_cache (Type -> TyCoVarSet
tyCoVarsOfType Type
hole_ty)
               -- The 'False' means "don't filter the bindings"; see #8191

       ; show_hole_constraints <- goptM Opt_ShowHoleConstraints
       ; let relevant_cts
               | ExprHole HoleExprRef
_ <- HoleSort
sort, Bool
show_hole_constraints
               = SolverReportErrCtxt -> [(Type, RealSrcSpan)]
givenConstraints SolverReportErrCtxt
ctxt
               | Bool
otherwise
               = []

       ; show_valid_hole_fits <- goptM Opt_ShowValidHoleFits
       ; (ctxt, hole_fits) <- if show_valid_hole_fits
                              then validHoleFits ctxt tidy_simples hole
                              else return (ctxt, noValidHoleFits)
       ; (grouped_skvs, other_tvs) <- liftZonkM $ zonkAndGroupSkolTvs hole_ty
       ; let reason | ExprHole HoleExprRef
_ <- HoleSort
sort = SolverReportErrCtxt -> DiagnosticReason
cec_expr_holes SolverReportErrCtxt
ctxt
                    | Bool
otherwise          = SolverReportErrCtxt -> DiagnosticReason
cec_type_holes SolverReportErrCtxt
ctxt
             err  = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReportWithCtxt
SolverReportWithCtxt SolverReportErrCtxt
ctxt
                  (TcSolverReportMsg -> SolverReportWithCtxt)
-> TcSolverReportMsg -> SolverReportWithCtxt
forall a b. (a -> b) -> a -> b
$ Hole -> HoleError -> TcSolverReportMsg
ReportHoleError Hole
hole
                  (HoleError -> TcSolverReportMsg) -> HoleError -> TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$ HoleSort -> [TcId] -> [(SkolemInfoAnon, [TcId])] -> HoleError
HoleError HoleSort
sort [TcId]
other_tvs [(SkolemInfoAnon, [TcId])]
grouped_skvs
             supp = [ RelevantBindings -> SolverReportSupplementary
SupplementaryBindings RelevantBindings
rel_binds
                    , [(Type, RealSrcSpan)] -> SolverReportSupplementary
SupplementaryCts      [(Type, RealSrcSpan)]
relevant_cts
                    , ValidHoleFits -> SolverReportSupplementary
SupplementaryHoleFits ValidHoleFits
hole_fits ]

       ; maybeAddDeferredBindings ctxt hole (SolverReport err supp)

       ; mkErrorReport lcl_env (TcRnSolverReport err reason) (Just ctxt) supp
       }

  where
    lcl_env :: CtLocEnv
lcl_env = CtLoc -> CtLocEnv
ctLocEnv CtLoc
ct_loc

-- | For all the skolem type variables in a type, zonk the skolem info and group together
-- all the type variables with the same origin.
zonkAndGroupSkolTvs :: Type -> ZonkM ([(SkolemInfoAnon, [TcTyVar])], [TcTyVar])
zonkAndGroupSkolTvs :: Type -> ZonkM ([(SkolemInfoAnon, [TcId])], [TcId])
zonkAndGroupSkolTvs Type
hole_ty = do
  zonked_info <- ((SkolemInfo, [(TcId, Int)]) -> ZonkM (SkolemInfoAnon, [TcId]))
-> [(SkolemInfo, [(TcId, Int)])]
-> ZonkM [(SkolemInfoAnon, [TcId])]
forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
forall (m :: * -> *) a b. Monad m => (a -> m b) -> [a] -> m [b]
mapM (SkolemInfo, [(TcId, Int)]) -> ZonkM (SkolemInfoAnon, [TcId])
forall {f :: * -> *} {b} {b}.
Functor f =>
(SkolemInfo, f (b, b)) -> ZonkM (SkolemInfoAnon, f b)
zonk_skolem_info [(SkolemInfo, [(TcId, Int)])]
skolem_list
  return (zonked_info, other_tvs)
  where
    zonk_skolem_info :: (SkolemInfo, f (b, b)) -> ZonkM (SkolemInfoAnon, f b)
zonk_skolem_info (SkolemInfo
sk, f (b, b)
tv) =
      do { sk <- SkolemInfoAnon -> ZonkM SkolemInfoAnon
zonkSkolemInfoAnon (SkolemInfoAnon -> ZonkM SkolemInfoAnon)
-> SkolemInfoAnon -> ZonkM SkolemInfoAnon
forall a b. (a -> b) -> a -> b
$ SkolemInfo -> SkolemInfoAnon
getSkolemInfo SkolemInfo
sk
         ; return (sk, fst <$> tv) }
    tvs :: [TcId]
tvs = Type -> [TcId]
tyCoVarsOfTypeList Type
hole_ty
    ([TcId]
skol_tvs, [TcId]
other_tvs) = (TcId -> Bool) -> [TcId] -> ([TcId], [TcId])
forall a. (a -> Bool) -> [a] -> ([a], [a])
partition (TcId -> Bool
isTcTyVar (TcId -> Bool) -> (TcId -> Bool) -> TcId -> Bool
forall (f :: * -> *). Applicative f => f Bool -> f Bool -> f Bool
<&&> TcId -> Bool
isSkolemTyVar) [TcId]
tvs

    group_skolems :: UM.UniqMap SkolemInfo ([(TcTyVar, Int)])
    group_skolems :: UniqMap SkolemInfo [(TcId, Int)]
group_skolems = Bag (TcId, Int) -> [(TcId, Int)]
forall a. Bag a -> [a]
bagToList (Bag (TcId, Int) -> [(TcId, Int)])
-> UniqMap SkolemInfo (Bag (TcId, Int))
-> UniqMap SkolemInfo [(TcId, Int)]
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$>
      (Bag (TcId, Int) -> Bag (TcId, Int) -> Bag (TcId, Int))
-> [(SkolemInfo, Bag (TcId, Int))]
-> UniqMap SkolemInfo (Bag (TcId, Int))
forall k a. Uniquable k => (a -> a -> a) -> [(k, a)] -> UniqMap k a
UM.listToUniqMap_C Bag (TcId, Int) -> Bag (TcId, Int) -> Bag (TcId, Int)
forall a. Bag a -> Bag a -> Bag a
unionBags
        [(TcId -> SkolemInfo
skolemSkolInfo TcId
tv, (TcId, Int) -> Bag (TcId, Int)
forall a. a -> Bag a
unitBag (TcId
tv, Int
n)) | TcId
tv <- [TcId]
skol_tvs | Int
n <- [Int
0..]]

    skolem_list :: [(SkolemInfo, [(TcId, Int)])]
skolem_list = ((SkolemInfo, [(TcId, Int)])
 -> (SkolemInfo, [(TcId, Int)]) -> Ordering)
-> [(SkolemInfo, [(TcId, Int)])] -> [(SkolemInfo, [(TcId, Int)])]
forall a. (a -> a -> Ordering) -> [a] -> [a]
sortBy (((SkolemInfo, [(TcId, Int)]) -> [Int])
-> (SkolemInfo, [(TcId, Int)])
-> (SkolemInfo, [(TcId, Int)])
-> Ordering
forall a b. Ord a => (b -> a) -> b -> b -> Ordering
comparing ([Int] -> [Int]
forall a. Ord a => [a] -> [a]
sort ([Int] -> [Int])
-> ((SkolemInfo, [(TcId, Int)]) -> [Int])
-> (SkolemInfo, [(TcId, Int)])
-> [Int]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ((TcId, Int) -> Int) -> [(TcId, Int)] -> [Int]
forall a b. (a -> b) -> [a] -> [b]
map (TcId, Int) -> Int
forall a b. (a, b) -> b
snd ([(TcId, Int)] -> [Int])
-> ((SkolemInfo, [(TcId, Int)]) -> [(TcId, Int)])
-> (SkolemInfo, [(TcId, Int)])
-> [Int]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (SkolemInfo, [(TcId, Int)]) -> [(TcId, Int)]
forall a b. (a, b) -> b
snd))
                ([(SkolemInfo, [(TcId, Int)])] -> [(SkolemInfo, [(TcId, Int)])])
-> [(SkolemInfo, [(TcId, Int)])] -> [(SkolemInfo, [(TcId, Int)])]
forall a b. (a -> b) -> a -> b
$ UniqMap SkolemInfo [(TcId, Int)] -> [(SkolemInfo, [(TcId, Int)])]
forall k a. UniqMap k a -> [(k, a)]
UM.nonDetUniqMapToList UniqMap SkolemInfo [(TcId, Int)]
group_skolems

{- Note [Adding deferred bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When working with typed holes we have to deal with the case where
we want holes to be reported as warnings to users during compile time but
as errors during runtime. Therefore, we have to call 'maybeAddDeferredBindings'
so that the correct 'Severity' can be computed out of that later on.
-}


-- | Adds deferred bindings (as errors).
-- See Note [Adding deferred bindings].
maybeAddDeferredBindings :: SolverReportErrCtxt
                         -> Hole
                         -> SolverReport
                         -> TcM ()
maybeAddDeferredBindings :: SolverReportErrCtxt -> Hole -> SolverReport -> TcM ()
maybeAddDeferredBindings SolverReportErrCtxt
ctxt Hole
hole SolverReport
report = do
  case Hole -> HoleSort
hole_sort Hole
hole of
    ExprHole (HER IORef EvTerm
ref Type
ref_ty Unique
_) -> do
      -- Only add bindings for holes in expressions
      -- not for holes in partial type signatures
      -- cf. addDeferredBinding
      Bool -> TcM () -> TcM ()
forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (SolverReportErrCtxt -> Bool
deferringAnyBindings SolverReportErrCtxt
ctxt) (TcM () -> TcM ()) -> TcM () -> TcM ()
forall a b. (a -> b) -> a -> b
$ do
        err_tm <- SolverReportErrCtxt -> CtLoc -> Type -> SolverReport -> TcM EvTerm
mkErrorTerm SolverReportErrCtxt
ctxt (Hole -> CtLoc
hole_loc Hole
hole) Type
ref_ty SolverReport
report
          -- NB: ref_ty, not hole_ty. hole_ty might be rewritten.
          -- See Note [Holes] in GHC.Tc.Types.Constraint
        writeMutVar ref err_tm
    HoleSort
_ -> () -> TcM ()
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (f :: * -> *) a. Applicative f => a -> f a
pure ()

-- We unwrap the SolverReportErrCtxt here, to avoid introducing a loop in module
-- imports
validHoleFits :: SolverReportErrCtxt    -- ^ The context we're in, i.e. the
                                        -- implications and the tidy environment
              -> [ErrorItem]      -- ^ Unsolved simple constraints
              -> Hole             -- ^ The hole
              -> TcM (SolverReportErrCtxt, ValidHoleFits)
                -- ^ We return the new context
                -- with a possibly updated
                -- tidy environment, and
                -- the valid hole fits.
validHoleFits :: SolverReportErrCtxt
-> [ErrorItem] -> Hole -> TcM (SolverReportErrCtxt, ValidHoleFits)
validHoleFits ctxt :: SolverReportErrCtxt
ctxt@(CEC { cec_encl :: SolverReportErrCtxt -> [Implication]
cec_encl = [Implication]
implics
                        , cec_tidy :: SolverReportErrCtxt -> TidyEnv
cec_tidy = TidyEnv
lcl_env}) [ErrorItem]
simps Hole
hole
  = do { (tidy_env, fits) <- TidyEnv
-> [Implication]
-> [CtEvidence]
-> Hole
-> TcM (TidyEnv, ValidHoleFits)
findValidHoleFits TidyEnv
lcl_env [Implication]
implics ((ErrorItem -> Maybe CtEvidence) -> [ErrorItem] -> [CtEvidence]
forall a b. (a -> Maybe b) -> [a] -> [b]
mapMaybe ErrorItem -> Maybe CtEvidence
mk_wanted [ErrorItem]
simps) Hole
hole
       ; return (ctxt {cec_tidy = tidy_env}, fits) }
  where
    mk_wanted :: ErrorItem -> Maybe CtEvidence
    mk_wanted :: ErrorItem -> Maybe CtEvidence
mk_wanted (EI { ei_pred :: ErrorItem -> Type
ei_pred = Type
pred, ei_evdest :: ErrorItem -> Maybe TcEvDest
ei_evdest = Maybe TcEvDest
m_dest, ei_loc :: ErrorItem -> CtLoc
ei_loc = CtLoc
loc })
      | Just TcEvDest
dest <- Maybe TcEvDest
m_dest
      = CtEvidence -> Maybe CtEvidence
forall a. a -> Maybe a
Just (CtWanted { ctev_pred :: Type
ctev_pred      = Type
pred
                       , ctev_dest :: TcEvDest
ctev_dest      = TcEvDest
dest
                       , ctev_loc :: CtLoc
ctev_loc       = CtLoc
loc
                       , ctev_rewriters :: RewriterSet
ctev_rewriters = RewriterSet
emptyRewriterSet })
      | Bool
otherwise
      = Maybe CtEvidence
forall a. Maybe a
Nothing   -- The ErrorItem was a Given


-- See Note [Constraints include ...]
givenConstraints :: SolverReportErrCtxt -> [(Type, RealSrcSpan)]
givenConstraints :: SolverReportErrCtxt -> [(Type, RealSrcSpan)]
givenConstraints SolverReportErrCtxt
ctxt
  = do { implic@Implic{ ic_given = given } <- SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt
       ; constraint <- given
       ; return (varType constraint, getCtLocEnvLoc (ic_env implic)) }

----------------

mkIPErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
-- What would happen if an item is suppressed because of
-- Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint? Very unclear
-- what's best. Let's not worry about this.
mkIPErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkIPErr SolverReportErrCtxt
ctxt (ErrorItem
item1:|[ErrorItem]
others)
  = do { (ctxt, binds, item1) <- Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
True SolverReportErrCtxt
ctxt ErrorItem
item1
       ; let msg = SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important SolverReportErrCtxt
ctxt (TcSolverReportMsg -> SolverReport)
-> TcSolverReportMsg -> SolverReport
forall a b. (a -> b) -> a -> b
$ NonEmpty ErrorItem -> TcSolverReportMsg
UnboundImplicitParams (ErrorItem
item1 ErrorItem -> [ErrorItem] -> NonEmpty ErrorItem
forall a. a -> [a] -> NonEmpty a
:| [ErrorItem]
others)
       ; return $ add_relevant_bindings binds msg }

----------------

-- | Report a representation-polymorphism error to the user:
-- a type is required to have a fixed runtime representation,
-- but doesn't.
--
-- See Note [Reporting representation-polymorphism errors] in GHC.Tc.Types.Origin.
mkFRRErr :: HasDebugCallStack => SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkFRRErr :: HasDebugCallStack =>
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkFRRErr SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  = do { -- Process the error items.
       ; (_tidy_env, frr_infos) <-
          ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
-> TcM (TidyEnv, [FixedRuntimeRepErrorInfo])
forall a. ZonkM a -> TcM a
liftZonkM (ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
 -> TcM (TidyEnv, [FixedRuntimeRepErrorInfo]))
-> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
-> TcM (TidyEnv, [FixedRuntimeRepErrorInfo])
forall a b. (a -> b) -> a -> b
$ TidyEnv
-> [FixedRuntimeRepErrorInfo]
-> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
zonkTidyFRRInfos (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt) ([FixedRuntimeRepErrorInfo]
 -> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo]))
-> [FixedRuntimeRepErrorInfo]
-> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
forall a b. (a -> b) -> a -> b
$
            -- Zonk/tidy to show useful variable names.
          (FixedRuntimeRepErrorInfo -> FixedRuntimeRepErrorInfo -> Ordering)
-> [FixedRuntimeRepErrorInfo] -> [FixedRuntimeRepErrorInfo]
forall a. (a -> a -> Ordering) -> [a] -> [a]
nubOrdBy (Type -> Type -> Ordering
nonDetCmpType (Type -> Type -> Ordering)
-> (FixedRuntimeRepErrorInfo -> Type)
-> FixedRuntimeRepErrorInfo
-> FixedRuntimeRepErrorInfo
-> Ordering
forall b c a. (b -> b -> c) -> (a -> b) -> a -> a -> c
`on` (FixedRuntimeRepOrigin -> Type
frr_type (FixedRuntimeRepOrigin -> Type)
-> (FixedRuntimeRepErrorInfo -> FixedRuntimeRepOrigin)
-> FixedRuntimeRepErrorInfo
-> Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. FixedRuntimeRepErrorInfo -> FixedRuntimeRepOrigin
frr_info_origin)) ([FixedRuntimeRepErrorInfo] -> [FixedRuntimeRepErrorInfo])
-> [FixedRuntimeRepErrorInfo] -> [FixedRuntimeRepErrorInfo]
forall a b. (a -> b) -> a -> b
$
            -- Remove duplicates: only one representation-polymorphism error per type.
          (ErrorItem -> FixedRuntimeRepErrorInfo)
-> [ErrorItem] -> [FixedRuntimeRepErrorInfo]
forall a b. (a -> b) -> [a] -> [b]
map (String
-> Maybe FixedRuntimeRepErrorInfo -> FixedRuntimeRepErrorInfo
forall a. HasCallStack => String -> Maybe a -> a
expectJust String
"mkFRRErr" (Maybe FixedRuntimeRepErrorInfo -> FixedRuntimeRepErrorInfo)
-> (ErrorItem -> Maybe FixedRuntimeRepErrorInfo)
-> ErrorItem
-> FixedRuntimeRepErrorInfo
forall b c a. (b -> c) -> (a -> b) -> a -> c
. HasDebugCallStack => ErrorItem -> Maybe FixedRuntimeRepErrorInfo
ErrorItem -> Maybe FixedRuntimeRepErrorInfo
fixedRuntimeRepOrigin_maybe) ([ErrorItem] -> [FixedRuntimeRepErrorInfo])
-> [ErrorItem] -> [FixedRuntimeRepErrorInfo]
forall a b. (a -> b) -> a -> b
$
          NonEmpty ErrorItem -> [ErrorItem]
forall a. NonEmpty a -> [a]
forall (t :: * -> *) a. Foldable t => t a -> [a]
toList NonEmpty ErrorItem
items
       ; return $ important ctxt $ FixedRuntimeRepError frr_infos }

-- | Whether to report something using the @FixedRuntimeRep@ mechanism.
fixedRuntimeRepOrigin_maybe :: HasDebugCallStack => ErrorItem -> Maybe FixedRuntimeRepErrorInfo
fixedRuntimeRepOrigin_maybe :: HasDebugCallStack => ErrorItem -> Maybe FixedRuntimeRepErrorInfo
fixedRuntimeRepOrigin_maybe ErrorItem
item
  -- An error that arose directly from a representation-polymorphism check.
  | FRROrigin FixedRuntimeRepOrigin
frr_orig <- ErrorItem -> CtOrigin
errorItemOrigin ErrorItem
item
  = FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a. a -> Maybe a
Just (FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo)
-> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a b. (a -> b) -> a -> b
$ FRR_Info { frr_info_origin :: FixedRuntimeRepOrigin
frr_info_origin = FixedRuntimeRepOrigin
frr_orig
                    , frr_info_not_concrete :: Maybe (TcId, Type)
frr_info_not_concrete = Maybe (TcId, Type)
forall a. Maybe a
Nothing }
  -- A nominal equality involving a concrete type variable,
  -- such as @alpha[conc] ~# rr[sk]@ or @beta[conc] ~# RR@ for a
  -- type family application @RR@.
  | EqPred EqRel
NomEq Type
ty1 Type
ty2 <- Type -> Pred
classifyPredType (ErrorItem -> Type
errorItemPred ErrorItem
item)
  = if | Just (TcId
tv1, ConcreteFRR FixedRuntimeRepOrigin
frr1) <- Type -> Maybe (TcId, ConcreteTvOrigin)
isConcreteTyVarTy_maybe Type
ty1
       -> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a. a -> Maybe a
Just (FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo)
-> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a b. (a -> b) -> a -> b
$ FixedRuntimeRepOrigin
-> Maybe (TcId, Type) -> FixedRuntimeRepErrorInfo
FRR_Info FixedRuntimeRepOrigin
frr1 ((TcId, Type) -> Maybe (TcId, Type)
forall a. a -> Maybe a
Just (TcId
tv1, Type
ty2))
       | Just (TcId
tv2, ConcreteFRR FixedRuntimeRepOrigin
frr2) <- Type -> Maybe (TcId, ConcreteTvOrigin)
isConcreteTyVarTy_maybe Type
ty2
       -> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a. a -> Maybe a
Just (FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo)
-> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a b. (a -> b) -> a -> b
$ FixedRuntimeRepOrigin
-> Maybe (TcId, Type) -> FixedRuntimeRepErrorInfo
FRR_Info FixedRuntimeRepOrigin
frr2 ((TcId, Type) -> Maybe (TcId, Type)
forall a. a -> Maybe a
Just (TcId
tv2, Type
ty1))
       | Bool
otherwise
       -> Maybe FixedRuntimeRepErrorInfo
forall a. Maybe a
Nothing
  | Bool
otherwise
  = Maybe FixedRuntimeRepErrorInfo
forall a. Maybe a
Nothing

{-
Note [Constraints include ...]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'givenConstraintsMsg' returns the "Constraints include ..." message enabled by
-fshow-hole-constraints. For example, the following hole:

    foo :: (Eq a, Show a) => a -> String
    foo x = _

would generate the message:

    Constraints include
      Eq a (from foo.hs:1:1-36)
      Show a (from foo.hs:1:1-36)

Constraints are displayed in order from innermost (closest to the hole) to
outermost. There's currently no filtering or elimination of duplicates.

************************************************************************
*                                                                      *
                Equality errors
*                                                                      *
************************************************************************

Note [Inaccessible code]
~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   data T a where
     T1 :: T a
     T2 :: T Bool

   f :: (a ~ Int) => T a -> Int
   f T1 = 3
   f T2 = 4   -- Unreachable code

Here the second equation is unreachable. The original constraint
(a~Int) from the signature gets rewritten by the pattern-match to
(Bool~Int), so the danger is that we report the error as coming from
the *signature* (#7293).  So, for Given errors we replace the
env (and hence src-loc) on its CtLoc with that from the immediately
enclosing implication.

Note [Error messages for untouchables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider (#9109)
  data G a where { GBool :: G Bool }
  foo x = case x of GBool -> True

Here we can't solve (t ~ Bool), where t is the untouchable result
meta-var 't', because of the (a ~ Bool) from the pattern match.
So we infer the type
   f :: forall a t. G a -> t
making the meta-var 't' into a skolem.  So when we come to report
the unsolved (t ~ Bool), t won't look like an untouchable meta-var
any more.  So we don't assert that it is.
-}

-- Don't have multiple equality errors from the same location
-- E.g.   (Int,Bool) ~ (Bool,Int)   one error will do!
mkEqErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr :: SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkEqErr SolverReportErrCtxt
ctxt NonEmpty ErrorItem
items
  | ErrorItem
item1 :| [ErrorItem]
_ <- (ErrorItem -> Bool) -> NonEmpty ErrorItem -> NonEmpty ErrorItem
forall a. (a -> Bool) -> NonEmpty a -> NonEmpty a
tryFilter (Bool -> Bool
not (Bool -> Bool) -> (ErrorItem -> Bool) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> Bool
ei_suppress) NonEmpty ErrorItem
items
  = SolverReportErrCtxt -> ErrorItem -> TcM SolverReport
mkEqErr1 SolverReportErrCtxt
ctxt ErrorItem
item1

mkEqErr1 :: SolverReportErrCtxt -> ErrorItem -> TcM SolverReport
mkEqErr1 :: SolverReportErrCtxt -> ErrorItem -> TcM SolverReport
mkEqErr1 SolverReportErrCtxt
ctxt ErrorItem
item   -- Wanted only
                     -- givens handled in mkGivenErrorReporter
  = do { (ctxt, binds, item) <- Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
True SolverReportErrCtxt
ctxt ErrorItem
item
       ; traceTc "mkEqErr1" (ppr item $$ pprCtOrigin (errorItemOrigin item))
       ; err_msg <- mkEqErr_help ctxt item ty1 ty2
       ; let
           report = RelevantBindings -> SolverReport -> SolverReport
add_relevant_bindings RelevantBindings
binds
                  (SolverReport -> SolverReport) -> SolverReport -> SolverReport
forall a b. (a -> b) -> a -> b
$ SolverReportErrCtxt -> TcSolverReportMsg -> SolverReport
important SolverReportErrCtxt
ctxt TcSolverReportMsg
err_msg
       ; return report }
  where
    (Type
ty1, Type
ty2) = Type -> (Type, Type)
getEqPredTys (ErrorItem -> Type
errorItemPred ErrorItem
item)

-- | This function tries to reconstruct why a "Coercible ty1 ty2" constraint
-- is left over.
mkCoercibleExplanation :: GlobalRdrEnv -> FamInstEnvs
                       -> TcType -> TcType -> Maybe CoercibleMsg
mkCoercibleExplanation :: GlobalRdrEnv -> FamInstEnvs -> Type -> Type -> Maybe CoercibleMsg
mkCoercibleExplanation GlobalRdrEnv
rdr_env FamInstEnvs
fam_envs Type
ty1 Type
ty2
  | Just (TyCon
tc, [Type]
tys) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty1
  , (TyCon
rep_tc, [Type]
_, TcCoercionN
_) <- FamInstEnvs -> TyCon -> [Type] -> (TyCon, [Type], TcCoercionN)
tcLookupDataFamInst FamInstEnvs
fam_envs TyCon
tc [Type]
tys
  , Just CoercibleMsg
msg <- TyCon -> Maybe CoercibleMsg
coercible_msg_for_tycon TyCon
rep_tc
  = CoercibleMsg -> Maybe CoercibleMsg
forall a. a -> Maybe a
Just CoercibleMsg
msg
  | Just (TyCon
tc, [Type]
tys) <- HasDebugCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
splitTyConApp_maybe Type
ty2
  , (TyCon
rep_tc, [Type]
_, TcCoercionN
_) <- FamInstEnvs -> TyCon -> [Type] -> (TyCon, [Type], TcCoercionN)
tcLookupDataFamInst FamInstEnvs
fam_envs TyCon
tc [Type]
tys
  , Just CoercibleMsg
msg <- TyCon -> Maybe CoercibleMsg
coercible_msg_for_tycon TyCon
rep_tc
  = CoercibleMsg -> Maybe CoercibleMsg
forall a. a -> Maybe a
Just CoercibleMsg
msg
  | Just (Type
s1, Type
_) <- Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty1
  , Just (Type
s2, Type
_) <- Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty2
  , Type
s1 Type -> Type -> Bool
`eqType` Type
s2
  , Type -> Bool
has_unknown_roles Type
s1
  = CoercibleMsg -> Maybe CoercibleMsg
forall a. a -> Maybe a
Just (CoercibleMsg -> Maybe CoercibleMsg)
-> CoercibleMsg -> Maybe CoercibleMsg
forall a b. (a -> b) -> a -> b
$ Type -> CoercibleMsg
UnknownRoles Type
s1
  | Bool
otherwise
  = Maybe CoercibleMsg
forall a. Maybe a
Nothing
  where
    coercible_msg_for_tycon :: TyCon -> Maybe CoercibleMsg
coercible_msg_for_tycon TyCon
tc
        | TyCon -> Bool
isAbstractTyCon TyCon
tc
        = CoercibleMsg -> Maybe CoercibleMsg
forall a. a -> Maybe a
Just (CoercibleMsg -> Maybe CoercibleMsg)
-> CoercibleMsg -> Maybe CoercibleMsg
forall a b. (a -> b) -> a -> b
$ TyCon -> CoercibleMsg
TyConIsAbstract TyCon
tc
        | TyCon -> Bool
isNewTyCon TyCon
tc
        , [DataCon
data_con] <- TyCon -> [DataCon]
tyConDataCons TyCon
tc
        , let dc_name :: Name
dc_name = DataCon -> Name
dataConName DataCon
data_con
        , Maybe (GlobalRdrEltX GREInfo) -> Bool
forall a. Maybe a -> Bool
isNothing (GlobalRdrEnv -> Name -> Maybe (GlobalRdrEltX GREInfo)
forall info.
Outputable info =>
GlobalRdrEnvX info -> Name -> Maybe (GlobalRdrEltX info)
lookupGRE_Name GlobalRdrEnv
rdr_env Name
dc_name)
        = CoercibleMsg -> Maybe CoercibleMsg
forall a. a -> Maybe a
Just (CoercibleMsg -> Maybe CoercibleMsg)
-> CoercibleMsg -> Maybe CoercibleMsg
forall a b. (a -> b) -> a -> b
$ TyCon -> DataCon -> CoercibleMsg
OutOfScopeNewtypeConstructor TyCon
tc DataCon
data_con
        | Bool
otherwise = Maybe CoercibleMsg
forall a. Maybe a
Nothing

    has_unknown_roles :: Type -> Bool
has_unknown_roles Type
ty
      | Just (TyCon
tc, [Type]
tys) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty
      = [Type]
tys [Type] -> Int -> Bool
forall a. [a] -> Int -> Bool
`lengthAtLeast` TyCon -> Int
tyConArity TyCon
tc  -- oversaturated tycon
      | Just (Type
s, Type
_) <- Type -> Maybe (Type, Type)
tcSplitAppTy_maybe Type
ty
      = Type -> Bool
has_unknown_roles Type
s
      | Type -> Bool
isTyVarTy Type
ty
      = Bool
True
      | Bool
otherwise
      = Bool
False

mkEqErr_help :: SolverReportErrCtxt
             -> ErrorItem
             -> TcType -> TcType -> TcM TcSolverReportMsg
mkEqErr_help :: SolverReportErrCtxt
-> ErrorItem -> Type -> Type -> TcM TcSolverReportMsg
mkEqErr_help SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2
  | Just (TcId, TcCoercionN)
casted_tv1 <- Type -> Maybe (TcId, TcCoercionN)
getCastedTyVar_maybe Type
ty1
  = SolverReportErrCtxt
-> ErrorItem
-> (TcId, TcCoercionN)
-> Type
-> TcM TcSolverReportMsg
mkTyVarEqErr SolverReportErrCtxt
ctxt ErrorItem
item (TcId, TcCoercionN)
casted_tv1 Type
ty2

  -- ToDo: explain..  Cf T2627b   Dual (Dual a) ~ a
  | Just (TcId, TcCoercionN)
casted_tv2 <- Type -> Maybe (TcId, TcCoercionN)
getCastedTyVar_maybe Type
ty2
  = SolverReportErrCtxt
-> ErrorItem
-> (TcId, TcCoercionN)
-> Type
-> TcM TcSolverReportMsg
mkTyVarEqErr SolverReportErrCtxt
ctxt ErrorItem
item (TcId, TcCoercionN)
casted_tv2 Type
ty1

  | Bool
otherwise
  = SolverReportErrCtxt
-> ErrorItem -> Type -> Type -> TcM TcSolverReportMsg
reportEqErr SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2

reportEqErr :: SolverReportErrCtxt
            -> ErrorItem
            -> TcType -> TcType
            -> TcM TcSolverReportMsg
reportEqErr :: SolverReportErrCtxt
-> ErrorItem -> Type -> Type -> TcM TcSolverReportMsg
reportEqErr SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2
  = do
    mb_coercible_info <- if ErrorItem -> EqRel
errorItemEqRel ErrorItem
item EqRel -> EqRel -> Bool
forall a. Eq a => a -> a -> Bool
== EqRel
ReprEq
                         then Type -> Type -> TcM (Maybe CoercibleMsg)
coercible_msg Type
ty1 Type
ty2
                         else Maybe CoercibleMsg -> TcM (Maybe CoercibleMsg)
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe CoercibleMsg
forall a. Maybe a
Nothing
    tv_info <- case getTyVar_maybe ty2 of
                 Maybe TcId
Nothing  -> Maybe TyVarInfo -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TyVarInfo)
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe TyVarInfo
forall a. Maybe a
Nothing
                 Just TcId
tv2 -> TyVarInfo -> Maybe TyVarInfo
forall a. a -> Maybe a
Just (TyVarInfo -> Maybe TyVarInfo)
-> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
-> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TyVarInfo)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv2, Maybe Implication
forall a. Maybe a
Nothing) Type
ty1
    return $ Mismatch { mismatchMsg           = mismatch
                      , mismatchTyVarInfo     = tv_info
                      , mismatchAmbiguityInfo = eqInfos
                      , mismatchCoercibleInfo = mb_coercible_info }
  where
    mismatch :: MismatchMsg
mismatch = SolverReportErrCtxt -> ErrorItem -> Type -> Type -> MismatchMsg
misMatchOrCND SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2
    eqInfos :: [AmbiguityInfo]
eqInfos  = Type -> Type -> [AmbiguityInfo]
eqInfoMsgs Type
ty1 Type
ty2

coercible_msg :: TcType -> TcType -> TcM (Maybe CoercibleMsg)
coercible_msg :: Type -> Type -> TcM (Maybe CoercibleMsg)
coercible_msg Type
ty1 Type
ty2
  = do
    rdr_env  <- TcRn GlobalRdrEnv
getGlobalRdrEnv
    fam_envs <- tcGetFamInstEnvs
    return $ mkCoercibleExplanation rdr_env fam_envs ty1 ty2

mkTyVarEqErr :: SolverReportErrCtxt -> ErrorItem
             -> (TcTyVar, TcCoercionN) -> TcType -> TcM TcSolverReportMsg
-- tv1 and ty2 are already tidied
mkTyVarEqErr :: SolverReportErrCtxt
-> ErrorItem
-> (TcId, TcCoercionN)
-> Type
-> TcM TcSolverReportMsg
mkTyVarEqErr SolverReportErrCtxt
ctxt ErrorItem
item (TcId, TcCoercionN)
casted_tv1 Type
ty2
  = do { String -> SDoc -> TcM ()
traceTc String
"mkTyVarEqErr" (ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr ErrorItem
item SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ (TcId, TcCoercionN) -> SDoc
forall a. Outputable a => a -> SDoc
ppr (TcId, TcCoercionN)
casted_tv1 SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ty2)
       ; SolverReportErrCtxt
-> ErrorItem
-> (TcId, TcCoercionN)
-> Type
-> TcM TcSolverReportMsg
mkTyVarEqErr' SolverReportErrCtxt
ctxt ErrorItem
item (TcId, TcCoercionN)
casted_tv1 Type
ty2 }

mkTyVarEqErr' :: SolverReportErrCtxt -> ErrorItem
              -> (TcTyVar, TcCoercionN) -> TcType -> TcM TcSolverReportMsg
mkTyVarEqErr' :: SolverReportErrCtxt
-> ErrorItem
-> (TcId, TcCoercionN)
-> Type
-> TcM TcSolverReportMsg
mkTyVarEqErr' SolverReportErrCtxt
ctxt ErrorItem
item (TcId
tv1, TcCoercionN
co1) Type
ty2

  -- Is this a representation-polymorphism error, e.g.
  -- alpha[conc] ~# rr[sk] ? If so, handle that first.
  | Just FixedRuntimeRepErrorInfo
frr_info <- Maybe FixedRuntimeRepErrorInfo
mb_concrete_reason
  = do
      (_, infos) <- ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
-> TcM (TidyEnv, [FixedRuntimeRepErrorInfo])
forall a. ZonkM a -> TcM a
liftZonkM (ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
 -> TcM (TidyEnv, [FixedRuntimeRepErrorInfo]))
-> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
-> TcM (TidyEnv, [FixedRuntimeRepErrorInfo])
forall a b. (a -> b) -> a -> b
$ TidyEnv
-> [FixedRuntimeRepErrorInfo]
-> ZonkM (TidyEnv, [FixedRuntimeRepErrorInfo])
zonkTidyFRRInfos (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt) [FixedRuntimeRepErrorInfo
frr_info]
      return $ FixedRuntimeRepError infos

  -- Impredicativity is a simple error to understand;
  -- try it before anything more complicated.
  | CheckTyEqResult
check_eq_result CheckTyEqResult -> CheckTyEqProblem -> Bool
`cterHasProblem` CheckTyEqProblem
cteImpredicative
  = do
    tyvar_eq_info <- (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv1, Maybe Implication
forall a. Maybe a
Nothing) Type
ty2
    let
        poly_msg = ErrorItem
-> TcId -> Type -> Maybe TyVarInfo -> CannotUnifyVariableReason
CannotUnifyWithPolytype ErrorItem
item TcId
tv1 Type
ty2 Maybe TyVarInfo
mb_tv_info
        mb_tv_info
          | TcId -> Bool
isSkolemTyVar TcId
tv1
          = TyVarInfo -> Maybe TyVarInfo
forall a. a -> Maybe a
Just TyVarInfo
tyvar_eq_info
          | Bool
otherwise
          = Maybe TyVarInfo
forall a. Maybe a
Nothing
        main_msg =
          CannotUnifyVariable
            { mismatchMsg :: MismatchMsg
mismatchMsg       = MismatchMsg
headline_msg
            , cannotUnifyReason :: CannotUnifyVariableReason
cannotUnifyReason = CannotUnifyVariableReason
poly_msg }
        -- Unlike the other reports, this discards the old 'report_important'
        -- instead of augmenting it.  This is because the details are not likely
        -- to be helpful since this is just an unimplemented feature.
    return main_msg

  -- Incompatible kinds
  -- This is wrinkle (EIK2) in Note [Equalities with incompatible kinds]
  -- in GHC.Tc.Solver.Equality
  | TcCoercionN -> Bool
hasCoercionHoleCo TcCoercionN
co1 Bool -> Bool -> Bool
|| Type -> Bool
hasCoercionHoleTy Type
ty2
  = TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (TcSolverReportMsg -> TcM TcSolverReportMsg)
-> TcSolverReportMsg -> TcM TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$ ErrorItem -> TcSolverReportMsg
mkBlockedEqErr ErrorItem
item

  | TcId -> Bool
isSkolemTyVar TcId
tv1  -- ty2 won't be a meta-tyvar; we would have
                       -- swapped in Solver.Equality.canEqTyVarHomo
    Bool -> Bool -> Bool
|| TcId -> Bool
isTyVarTyVar TcId
tv1 Bool -> Bool -> Bool
&& Bool -> Bool
not (Type -> Bool
isTyVarTy Type
ty2)
    Bool -> Bool -> Bool
|| ErrorItem -> EqRel
errorItemEqRel ErrorItem
item EqRel -> EqRel -> Bool
forall a. Eq a => a -> a -> Bool
== EqRel
ReprEq
     -- The cases below don't really apply to ReprEq (except occurs check)
  = do
    tv_extra <- (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv1, Maybe Implication
forall a. Maybe a
Nothing) Type
ty2
    reason <- if errorItemEqRel item == ReprEq
              then RepresentationalEq tv_extra <$> coercible_msg ty1 ty2
              else return $ DifferentTyVars tv_extra
    let main_msg = CannotUnifyVariable
                     { mismatchMsg :: MismatchMsg
mismatchMsg       = MismatchMsg
headline_msg
                     , cannotUnifyReason :: CannotUnifyVariableReason
cannotUnifyReason = CannotUnifyVariableReason
reason }
    return main_msg

  | TcId
tv1 TcId -> TyCoVarSet -> Bool
`elemVarSet` Type -> TyCoVarSet
tyCoVarsOfType Type
ty2
    -- We report an "occurs check" even for  a ~ F t a, where F is a type
    -- function; it's not insoluble (because in principle F could reduce)
    -- but we have certainly been unable to solve it
    --
    -- Use tyCoVarsOfType because it might have begun as the canonical
    -- constraint (Dual (Dual a)) ~ a, and been swizzled by mkEqnErr_help
  = let ambiguity_infos :: [AmbiguityInfo]
ambiguity_infos = Type -> Type -> [AmbiguityInfo]
eqInfoMsgs Type
ty1 Type
ty2

        interesting_tyvars :: [TcId]
interesting_tyvars = (TcId -> Bool) -> [TcId] -> [TcId]
forall a. (a -> Bool) -> [a] -> [a]
filter (Bool -> Bool
not (Bool -> Bool) -> (TcId -> Bool) -> TcId -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Type -> Bool
noFreeVarsOfType (Type -> Bool) -> (TcId -> Type) -> TcId -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TcId -> Type
tyVarKind) ([TcId] -> [TcId]) -> [TcId] -> [TcId]
forall a b. (a -> b) -> a -> b
$
                             (TcId -> Bool) -> [TcId] -> [TcId]
forall a. (a -> Bool) -> [a] -> [a]
filter TcId -> Bool
isTyVar ([TcId] -> [TcId]) -> [TcId] -> [TcId]
forall a b. (a -> b) -> a -> b
$
                             FV -> [TcId]
fvVarList (FV -> [TcId]) -> FV -> [TcId]
forall a b. (a -> b) -> a -> b
$
                             Type -> FV
tyCoFVsOfType Type
ty1 FV -> FV -> FV
`unionFV` Type -> FV
tyCoFVsOfType Type
ty2

        occurs_err :: CannotUnifyVariableReason
occurs_err =
          OccursCheck
            { occursCheckInterestingTyVars :: [TcId]
occursCheckInterestingTyVars = [TcId]
interesting_tyvars
            , occursCheckAmbiguityInfos :: [AmbiguityInfo]
occursCheckAmbiguityInfos    = [AmbiguityInfo]
ambiguity_infos }
        main_msg :: TcSolverReportMsg
main_msg =
          CannotUnifyVariable
            { mismatchMsg :: MismatchMsg
mismatchMsg       = MismatchMsg
headline_msg
            , cannotUnifyReason :: CannotUnifyVariableReason
cannotUnifyReason = CannotUnifyVariableReason
occurs_err }

    in TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return TcSolverReportMsg
main_msg

  -- If the immediately-enclosing implication has 'tv' a skolem, and
  -- we know by now its an InferSkol kind of skolem, then presumably
  -- it started life as a TyVarTv, else it'd have been unified, given
  -- that there's no occurs-check or forall problem
  | (Implication
implic:[Implication]
_) <- SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt
  , Implic { ic_skols :: Implication -> [TcId]
ic_skols = [TcId]
skols } <- Implication
implic
  , TcId
tv1 TcId -> [TcId] -> Bool
forall a. Eq a => a -> [a] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [TcId]
skols
  = do
    tv_extra <- (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv1, Maybe Implication
forall a. Maybe a
Nothing) Type
ty2
    let msg = Mismatch
               { mismatchMsg :: MismatchMsg
mismatchMsg           = MismatchMsg
mismatch_msg
               , mismatchTyVarInfo :: Maybe TyVarInfo
mismatchTyVarInfo     = TyVarInfo -> Maybe TyVarInfo
forall a. a -> Maybe a
Just TyVarInfo
tv_extra
               , mismatchAmbiguityInfo :: [AmbiguityInfo]
mismatchAmbiguityInfo = []
               , mismatchCoercibleInfo :: Maybe CoercibleMsg
mismatchCoercibleInfo = Maybe CoercibleMsg
forall a. Maybe a
Nothing }
    return msg

  -- Check for skolem escape
  | (Implication
implic:[Implication]
_) <- SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt   -- Get the innermost context
  , Implic { ic_skols :: Implication -> [TcId]
ic_skols = [TcId]
skols } <- Implication
implic
  , let esc_skols :: [TcId]
esc_skols = (TcId -> Bool) -> [TcId] -> [TcId]
forall a. (a -> Bool) -> [a] -> [a]
filter (TcId -> TyCoVarSet -> Bool
`elemVarSet` (Type -> TyCoVarSet
tyCoVarsOfType Type
ty2)) [TcId]
skols
  , Bool -> Bool
not ([TcId] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TcId]
esc_skols)
  = let main_msg :: TcSolverReportMsg
main_msg =
          CannotUnifyVariable
            { mismatchMsg :: MismatchMsg
mismatchMsg       = MismatchMsg
mismatch_msg
            , cannotUnifyReason :: CannotUnifyVariableReason
cannotUnifyReason = ErrorItem -> Implication -> [TcId] -> CannotUnifyVariableReason
SkolemEscape ErrorItem
item Implication
implic [TcId]
esc_skols }

  in TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return TcSolverReportMsg
main_msg

  -- Nastiest case: attempt to unify an untouchable variable
  -- So tv is a meta tyvar (or started that way before we
  -- generalised it).  So presumably it is an *untouchable*
  -- meta tyvar or a TyVarTv, else it'd have been unified
  -- See Note [Error messages for untouchables]
  | (Implication
implic:[Implication]
_) <- SolverReportErrCtxt -> [Implication]
cec_encl SolverReportErrCtxt
ctxt   -- Get the innermost context
  , Implic { ic_tclvl :: Implication -> TcLevel
ic_tclvl = TcLevel
lvl } <- Implication
implic
  = Bool -> SDoc -> TcM TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr (Bool -> Bool
not (TcLevel -> TcId -> Bool
isTouchableMetaTyVar TcLevel
lvl TcId
tv1))
              (TcId -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcId
tv1 SDoc -> SDoc -> SDoc
forall doc. IsDoc doc => doc -> doc -> doc
$$ TcLevel -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcLevel
lvl) (TcM TcSolverReportMsg -> TcM TcSolverReportMsg)
-> TcM TcSolverReportMsg -> TcM TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$ do -- See Note [Error messages for untouchables]
    tv_extra <- (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv1, Implication -> Maybe Implication
forall a. a -> Maybe a
Just Implication
implic) Type
ty2
    let tv_extra' = TyVarInfo
tv_extra { thisTyVarIsUntouchable = Just implic }
        msg = Mismatch
               { mismatchMsg :: MismatchMsg
mismatchMsg           = MismatchMsg
mismatch_msg
               , mismatchTyVarInfo :: Maybe TyVarInfo
mismatchTyVarInfo     = TyVarInfo -> Maybe TyVarInfo
forall a. a -> Maybe a
Just TyVarInfo
tv_extra'
               , mismatchAmbiguityInfo :: [AmbiguityInfo]
mismatchAmbiguityInfo = []
               , mismatchCoercibleInfo :: Maybe CoercibleMsg
mismatchCoercibleInfo = Maybe CoercibleMsg
forall a. Maybe a
Nothing }
    return msg

  | Bool
otherwise
  = SolverReportErrCtxt
-> ErrorItem -> Type -> Type -> TcM TcSolverReportMsg
reportEqErr SolverReportErrCtxt
ctxt ErrorItem
item (TcId -> Type
mkTyVarTy TcId
tv1) Type
ty2
        -- This *can* happen (#6123)
        -- Consider an ambiguous top-level constraint (a ~ F a)
        -- Not an occurs check, because F is a type function.
  where
    headline_msg :: MismatchMsg
headline_msg = SolverReportErrCtxt -> ErrorItem -> Type -> Type -> MismatchMsg
misMatchOrCND SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2
    mismatch_msg :: MismatchMsg
mismatch_msg = ErrorItem -> Type -> Type -> MismatchMsg
mkMismatchMsg ErrorItem
item Type
ty1 Type
ty2

    -- The following doesn't use the cterHasProblem mechanism because
    -- we need to retrieve the ConcreteTvOrigin. Just knowing whether
    -- there is an error is not sufficient. See #21430.
    mb_concrete_reason :: Maybe FixedRuntimeRepErrorInfo
mb_concrete_reason
      | Just ConcreteTvOrigin
frr_orig <- TcId -> Maybe ConcreteTvOrigin
isConcreteTyVar_maybe TcId
tv1
      , Bool -> Bool
not (Type -> Bool
isConcreteType Type
ty2)
      = FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a. a -> Maybe a
Just (FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo)
-> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a b. (a -> b) -> a -> b
$ ConcreteTvOrigin -> TcId -> Type -> FixedRuntimeRepErrorInfo
frr_reason ConcreteTvOrigin
frr_orig TcId
tv1 Type
ty2
      | Just (TcId
tv2, ConcreteTvOrigin
frr_orig) <- Type -> Maybe (TcId, ConcreteTvOrigin)
isConcreteTyVarTy_maybe Type
ty2
      , Bool -> Bool
not (TcId -> Bool
isConcreteTyVar TcId
tv1)
      = FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a. a -> Maybe a
Just (FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo)
-> FixedRuntimeRepErrorInfo -> Maybe FixedRuntimeRepErrorInfo
forall a b. (a -> b) -> a -> b
$ ConcreteTvOrigin -> TcId -> Type -> FixedRuntimeRepErrorInfo
frr_reason ConcreteTvOrigin
frr_orig TcId
tv2 Type
ty1
      -- NB: if it's an unsolved equality in which both sides are concrete
      -- (e.g. a concrete type variable on both sides), then it's not a
      -- representation-polymorphism problem.
      | Bool
otherwise
      = Maybe FixedRuntimeRepErrorInfo
forall a. Maybe a
Nothing
    frr_reason :: ConcreteTvOrigin -> TcId -> Type -> FixedRuntimeRepErrorInfo
frr_reason (ConcreteFRR FixedRuntimeRepOrigin
frr_orig) TcId
conc_tv Type
not_conc
      = FRR_Info { frr_info_origin :: FixedRuntimeRepOrigin
frr_info_origin = FixedRuntimeRepOrigin
frr_orig
                 , frr_info_not_concrete :: Maybe (TcId, Type)
frr_info_not_concrete = (TcId, Type) -> Maybe (TcId, Type)
forall a. a -> Maybe a
Just (TcId
conc_tv, Type
not_conc) }

    ty1 :: Type
ty1 = TcId -> Type
mkTyVarTy TcId
tv1

    check_eq_result :: CheckTyEqResult
check_eq_result = case ErrorItem -> Maybe CtIrredReason
ei_m_reason ErrorItem
item of
      Just (NonCanonicalReason CheckTyEqResult
result) -> CheckTyEqResult
result
      Maybe CtIrredReason
_                                -> CheckTyEqResult
cteOK

eqInfoMsgs :: TcType -> TcType -> [AmbiguityInfo]
-- Report (a) ambiguity if either side is a type function application
--            e.g. F a0 ~ Int
--        (b) warning about injectivity if both sides are the same
--            type function application   F a ~ F b
--            See Note [Non-injective type functions]
eqInfoMsgs :: Type -> Type -> [AmbiguityInfo]
eqInfoMsgs Type
ty1 Type
ty2
  = [Maybe AmbiguityInfo] -> [AmbiguityInfo]
forall a. [Maybe a] -> [a]
catMaybes [Maybe AmbiguityInfo
tyfun_msg, Maybe AmbiguityInfo
ambig_msg]
  where
    mb_fun1 :: Maybe TyCon
mb_fun1 = Type -> Maybe TyCon
isTyFun_maybe Type
ty1
    mb_fun2 :: Maybe TyCon
mb_fun2 = Type -> Maybe TyCon
isTyFun_maybe Type
ty2

      -- if a type isn't headed by a type function, then any ambiguous
      -- variables need not be reported as such. e.g.: F a ~ t0 -> t0, where a is a skolem
    ambig_tkvs1 :: ([TcId], [TcId])
ambig_tkvs1 = ([TcId], [TcId])
-> (TyCon -> ([TcId], [TcId])) -> Maybe TyCon -> ([TcId], [TcId])
forall b a. b -> (a -> b) -> Maybe a -> b
maybe ([TcId], [TcId])
forall a. Monoid a => a
mempty (\TyCon
_ -> Type -> ([TcId], [TcId])
ambigTkvsOfTy Type
ty1) Maybe TyCon
mb_fun1
    ambig_tkvs2 :: ([TcId], [TcId])
ambig_tkvs2 = ([TcId], [TcId])
-> (TyCon -> ([TcId], [TcId])) -> Maybe TyCon -> ([TcId], [TcId])
forall b a. b -> (a -> b) -> Maybe a -> b
maybe ([TcId], [TcId])
forall a. Monoid a => a
mempty (\TyCon
_ -> Type -> ([TcId], [TcId])
ambigTkvsOfTy Type
ty2) Maybe TyCon
mb_fun2

    ambig_tkvs :: ([TcId], [TcId])
ambig_tkvs@([TcId]
ambig_kvs, [TcId]
ambig_tvs) = ([TcId], [TcId])
ambig_tkvs1 ([TcId], [TcId]) -> ([TcId], [TcId]) -> ([TcId], [TcId])
forall a. Semigroup a => a -> a -> a
S.<> ([TcId], [TcId])
ambig_tkvs2

    ambig_msg :: Maybe AmbiguityInfo
ambig_msg | Maybe TyCon -> Bool
forall a. Maybe a -> Bool
isJust Maybe TyCon
mb_fun1 Bool -> Bool -> Bool
|| Maybe TyCon -> Bool
forall a. Maybe a -> Bool
isJust Maybe TyCon
mb_fun2
              , Bool -> Bool
not ([TcId] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TcId]
ambig_kvs Bool -> Bool -> Bool
&& [TcId] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TcId]
ambig_tvs)
              = AmbiguityInfo -> Maybe AmbiguityInfo
forall a. a -> Maybe a
Just (AmbiguityInfo -> Maybe AmbiguityInfo)
-> AmbiguityInfo -> Maybe AmbiguityInfo
forall a b. (a -> b) -> a -> b
$ Bool -> ([TcId], [TcId]) -> AmbiguityInfo
Ambiguity Bool
False ([TcId], [TcId])
ambig_tkvs
              | Bool
otherwise
              = Maybe AmbiguityInfo
forall a. Maybe a
Nothing

    tyfun_msg :: Maybe AmbiguityInfo
tyfun_msg | Just TyCon
tc1 <- Maybe TyCon
mb_fun1
              , Just TyCon
tc2 <- Maybe TyCon
mb_fun2
              , TyCon
tc1 TyCon -> TyCon -> Bool
forall a. Eq a => a -> a -> Bool
== TyCon
tc2
              , Bool -> Bool
not (TyCon -> Role -> Bool
isInjectiveTyCon TyCon
tc1 Role
Nominal)
              = AmbiguityInfo -> Maybe AmbiguityInfo
forall a. a -> Maybe a
Just (AmbiguityInfo -> Maybe AmbiguityInfo)
-> AmbiguityInfo -> Maybe AmbiguityInfo
forall a b. (a -> b) -> a -> b
$ TyCon -> AmbiguityInfo
NonInjectiveTyFam TyCon
tc1
              | Bool
otherwise
              = Maybe AmbiguityInfo
forall a. Maybe a
Nothing

misMatchOrCND :: SolverReportErrCtxt -> ErrorItem
              -> TcType -> TcType -> MismatchMsg
-- If oriented then ty1 is actual, ty2 is expected
misMatchOrCND :: SolverReportErrCtxt -> ErrorItem -> Type -> Type -> MismatchMsg
misMatchOrCND SolverReportErrCtxt
ctxt ErrorItem
item Type
ty1 Type
ty2
  | Bool
insoluble_item   -- See Note [Insoluble mis-match]
    Bool -> Bool -> Bool
|| (Type -> Bool
isRigidTy Type
ty1 Bool -> Bool -> Bool
&& Type -> Bool
isRigidTy Type
ty2)
    Bool -> Bool -> Bool
|| (ErrorItem -> CtFlavour
ei_flavour ErrorItem
item CtFlavour -> CtFlavour -> Bool
forall a. Eq a => a -> a -> Bool
== CtFlavour
Given)
    Bool -> Bool -> Bool
|| [Implication] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Implication]
givens
  = -- If the equality is unconditionally insoluble
    -- or there is no context, don't report the context
    ErrorItem -> Type -> Type -> MismatchMsg
mkMismatchMsg ErrorItem
item Type
ty1 Type
ty2

  | Bool
otherwise
  = [Implication]
-> NonEmpty ErrorItem -> Maybe CND_Extra -> MismatchMsg
CouldNotDeduce [Implication]
givens (ErrorItem
item ErrorItem -> [ErrorItem] -> NonEmpty ErrorItem
forall a. a -> [a] -> NonEmpty a
:| []) (CND_Extra -> Maybe CND_Extra
forall a. a -> Maybe a
Just (CND_Extra -> Maybe CND_Extra) -> CND_Extra -> Maybe CND_Extra
forall a b. (a -> b) -> a -> b
$ TypeOrKind -> Type -> Type -> CND_Extra
CND_Extra TypeOrKind
level Type
ty1 Type
ty2)

  where
    insoluble_item :: Bool
insoluble_item = case ErrorItem -> Maybe CtIrredReason
ei_m_reason ErrorItem
item of
                       Maybe CtIrredReason
Nothing -> Bool
False
                       Just CtIrredReason
r  -> CtIrredReason -> Bool
isInsolubleReason CtIrredReason
r

    level :: TypeOrKind
level   = CtLoc -> Maybe TypeOrKind
ctLocTypeOrKind_maybe (ErrorItem -> CtLoc
errorItemCtLoc ErrorItem
item) Maybe TypeOrKind -> TypeOrKind -> TypeOrKind
forall a. Maybe a -> a -> a
`orElse` TypeOrKind
TypeLevel
    givens :: [Implication]
givens  = [ Implication
given | Implication
given <- SolverReportErrCtxt -> [Implication]
getUserGivens SolverReportErrCtxt
ctxt, Implication -> HasGivenEqs
ic_given_eqs Implication
given HasGivenEqs -> HasGivenEqs -> Bool
forall a. Eq a => a -> a -> Bool
/= HasGivenEqs
NoGivenEqs ]
              -- Keep only UserGivens that have some equalities.
              -- See Note [Suppress redundant givens during error reporting]

-- These are for the "blocked" equalities, as described in GHC.Tc.Solver.Equality
-- Note [Equalities with incompatible kinds], wrinkle (EIK2). There should
-- always be another unsolved wanted around, which will ordinarily suppress
-- this message. But this can still be printed out with -fdefer-type-errors
-- (sigh), so we must produce a message.
mkBlockedEqErr :: ErrorItem -> TcSolverReportMsg
mkBlockedEqErr :: ErrorItem -> TcSolverReportMsg
mkBlockedEqErr ErrorItem
item = ErrorItem -> TcSolverReportMsg
BlockedEquality ErrorItem
item

{-
Note [Suppress redundant givens during error reporting]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When GHC is unable to solve a constraint and prints out an error message, it
will print out what given constraints are in scope to provide some context to
the programmer. But we shouldn't print out /every/ given, since some of them
are not terribly helpful to diagnose type errors. Consider this example:

  foo :: Int :~: Int -> a :~: b -> a :~: c
  foo Refl Refl = Refl

When reporting that GHC can't solve (a ~ c), there are two givens in scope:
(Int ~ Int) and (a ~ b). But (Int ~ Int) is trivially soluble (i.e.,
redundant), so it's not terribly useful to report it in an error message.
To accomplish this, we discard any Implications that do not bind any
equalities by filtering the `givens` selected in `misMatchOrCND` (based on
the `ic_given_eqs` field of the Implication). Note that we discard givens
that have no equalities whatsoever, but we want to keep ones with only *local*
equalities, as these may be helpful to the user in understanding what went
wrong.

But this is not enough to avoid all redundant givens! Consider this example,
from #15361:

  goo :: forall (a :: Type) (b :: Type) (c :: Type).
         a :~~: b -> a :~~: c
  goo HRefl = HRefl

Matching on HRefl brings the /single/ given (* ~ *, a ~ b) into scope.
The (* ~ *) part arises due the kinds of (:~~:) being unified. More
importantly, (* ~ *) is redundant, so we'd like not to report it. However,
the Implication (* ~ *, a ~ b) /does/ bind an equality (as reported by its
ic_given_eqs field), so the test above will keep it wholesale.

To refine this given, we apply mkMinimalBySCs on it to extract just the (a ~ b)
part. This works because mkMinimalBySCs eliminates reflexive equalities in
addition to superclasses (see Note [Remove redundant provided dicts]
in GHC.Tc.TyCl.PatSyn).
-}

extraTyVarEqInfo :: (TcTyVar, Maybe Implication) -> TcType -> TcM TyVarInfo
-- Add on extra info about skolem constants
-- NB: The types themselves are already tidied
extraTyVarEqInfo :: (TcId, Maybe Implication)
-> Type -> IOEnv (Env TcGblEnv TcLclEnv) TyVarInfo
extraTyVarEqInfo (TcId
tv1, Maybe Implication
mb_implic) Type
ty2
  = do
      tv1_info <- TcId -> TcM TcId
extraTyVarInfo TcId
tv1
      ty2_info <- ty_extra ty2
      return $
        TyVarInfo
          { thisTyVar              = tv1_info
          , thisTyVarIsUntouchable = mb_implic
          , otherTy                = ty2_info }
  where
    ty_extra :: Type -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcId)
ty_extra Type
ty = case Type -> Maybe (TcId, TcCoercionN)
getCastedTyVar_maybe Type
ty of
                    Just (TcId
tv, TcCoercionN
_) -> TcId -> Maybe TcId
forall a. a -> Maybe a
Just (TcId -> Maybe TcId)
-> TcM TcId -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcId)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> TcId -> TcM TcId
extraTyVarInfo TcId
tv
                    Maybe (TcId, TcCoercionN)
Nothing      -> Maybe TcId -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe TcId)
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe TcId
forall a. Maybe a
Nothing

extraTyVarInfo :: TcTyVar -> TcM TyVar
extraTyVarInfo :: TcId -> TcM TcId
extraTyVarInfo TcId
tv = Bool -> SDoc -> TcM TcId -> TcM TcId
forall a. HasCallStack => Bool -> SDoc -> a -> a
assertPpr (TcId -> Bool
isTyVar TcId
tv) (TcId -> SDoc
forall a. Outputable a => a -> SDoc
ppr TcId
tv) (TcM TcId -> TcM TcId) -> TcM TcId -> TcM TcId
forall a b. (a -> b) -> a -> b
$
  case TcId -> TcTyVarDetails
tcTyVarDetails TcId
tv of
    SkolemTv SkolemInfo
skol_info TcLevel
lvl Bool
overlaps -> do
      new_skol_info <- ZonkM SkolemInfo -> TcM SkolemInfo
forall a. ZonkM a -> TcM a
liftZonkM (ZonkM SkolemInfo -> TcM SkolemInfo)
-> ZonkM SkolemInfo -> TcM SkolemInfo
forall a b. (a -> b) -> a -> b
$ SkolemInfo -> ZonkM SkolemInfo
zonkSkolemInfo SkolemInfo
skol_info
      return $ mkTcTyVar (tyVarName tv) (tyVarKind tv) (SkolemTv new_skol_info lvl overlaps)
    TcTyVarDetails
_ -> TcId -> TcM TcId
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return TcId
tv

--------------------
mkMismatchMsg :: ErrorItem -> Type -> Type -> MismatchMsg
mkMismatchMsg :: ErrorItem -> Type -> Type -> MismatchMsg
mkMismatchMsg ErrorItem
item Type
ty1 Type
ty2 =
  case CtOrigin
orig of
    TypeEqOrigin { Type
uo_actual :: Type
uo_actual :: CtOrigin -> Type
uo_actual, Type
uo_expected :: Type
uo_expected :: CtOrigin -> Type
uo_expected, uo_thing :: CtOrigin -> Maybe TypedThing
uo_thing = Maybe TypedThing
mb_thing } ->
      (TypeEqMismatch
        { teq_mismatch_ppr_explicit_kinds :: Bool
teq_mismatch_ppr_explicit_kinds = Bool
ppr_explicit_kinds
        , teq_mismatch_item :: ErrorItem
teq_mismatch_item = ErrorItem
item
        , teq_mismatch_ty1 :: Type
teq_mismatch_ty1  = Type
ty1
        , teq_mismatch_ty2 :: Type
teq_mismatch_ty2  = Type
ty2
        , teq_mismatch_actual :: Type
teq_mismatch_actual   = Type
uo_actual
        , teq_mismatch_expected :: Type
teq_mismatch_expected = Type
uo_expected
        , teq_mismatch_what :: Maybe TypedThing
teq_mismatch_what     = Maybe TypedThing
mb_thing
        , teq_mb_same_occ :: Maybe SameOccInfo
teq_mb_same_occ       = Type -> Type -> Maybe SameOccInfo
sameOccExtras Type
ty2 Type
ty1 })
    KindEqOrigin Type
cty1 Type
cty2 CtOrigin
sub_o Maybe TypeOrKind
mb_sub_t_or_k -> BasicMismatch
      { mismatch_ea :: MismatchEA
mismatch_ea           = MismatchEA
NoEA
      , mismatch_item :: ErrorItem
mismatch_item         = ErrorItem
item
      , mismatch_ty1 :: Type
mismatch_ty1          = Type
ty1
      , mismatch_ty2 :: Type
mismatch_ty2          = Type
ty2
      , mismatch_whenMatching :: Maybe WhenMatching
mismatch_whenMatching = WhenMatching -> Maybe WhenMatching
forall a. a -> Maybe a
Just (WhenMatching -> Maybe WhenMatching)
-> WhenMatching -> Maybe WhenMatching
forall a b. (a -> b) -> a -> b
$ Type -> Type -> CtOrigin -> Maybe TypeOrKind -> WhenMatching
WhenMatching Type
cty1 Type
cty2 CtOrigin
sub_o Maybe TypeOrKind
mb_sub_t_or_k
      , mismatch_mb_same_occ :: Maybe SameOccInfo
mismatch_mb_same_occ  = Maybe SameOccInfo
mb_same_occ
      }
    CtOrigin
_ -> BasicMismatch
      { mismatch_ea :: MismatchEA
mismatch_ea           = MismatchEA
NoEA
      , mismatch_item :: ErrorItem
mismatch_item         = ErrorItem
item
      , mismatch_ty1 :: Type
mismatch_ty1          = Type
ty1
      , mismatch_ty2 :: Type
mismatch_ty2          = Type
ty2
      , mismatch_whenMatching :: Maybe WhenMatching
mismatch_whenMatching = Maybe WhenMatching
forall a. Maybe a
Nothing
      , mismatch_mb_same_occ :: Maybe SameOccInfo
mismatch_mb_same_occ  = Maybe SameOccInfo
mb_same_occ
      }
  where
    orig :: CtOrigin
orig = ErrorItem -> CtOrigin
errorItemOrigin ErrorItem
item
    mb_same_occ :: Maybe SameOccInfo
mb_same_occ = Type -> Type -> Maybe SameOccInfo
sameOccExtras Type
ty2 Type
ty1
    ppr_explicit_kinds :: Bool
ppr_explicit_kinds = Type -> Type -> CtOrigin -> Bool
shouldPprWithExplicitKinds Type
ty1 Type
ty2 CtOrigin
orig

-- | Whether to print explicit kinds (with @-fprint-explicit-kinds@)
-- in an 'SDoc' when a type mismatch occurs to due invisible kind arguments.
--
-- This function first checks to see if the 'CtOrigin' argument is a
-- 'TypeEqOrigin'. If so, it first checks whether the equality is a visible
-- equality; if it's not, definitely print the kinds. Even if the equality is
-- a visible equality, check the expected/actual types to see if the types
-- have equal visible components. If the 'CtOrigin' is
-- not a 'TypeEqOrigin', fall back on the actual mismatched types themselves.
shouldPprWithExplicitKinds :: Type -> Type -> CtOrigin -> Bool
shouldPprWithExplicitKinds :: Type -> Type -> CtOrigin -> Bool
shouldPprWithExplicitKinds Type
_ty1 Type
_ty2 (TypeEqOrigin { uo_actual :: CtOrigin -> Type
uo_actual = Type
act
                                                   , uo_expected :: CtOrigin -> Type
uo_expected = Type
exp
                                                   , uo_visible :: CtOrigin -> Bool
uo_visible = Bool
vis })
  | Bool -> Bool
not Bool
vis   = Bool
True                  -- See tests T15870, T16204c
  | Bool
otherwise = Type -> Type -> Bool
tcEqTypeVis Type
act Type
exp   -- See tests T9171, T9144.
shouldPprWithExplicitKinds Type
ty1 Type
ty2 CtOrigin
_ct
  = Type -> Type -> Bool
tcEqTypeVis Type
ty1 Type
ty2

{- Note [Insoluble mis-match]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider [G] a ~ [a],  [W] a ~ [a] (#13674).  The Given is insoluble
so we don't use it for rewriting.  The Wanted is also insoluble, and
we don't solve it from the Given.  It's very confusing to say
    Cannot solve a ~ [a] from given constraints a ~ [a]

And indeed even thinking about the Givens is silly; [W] a ~ [a] is
just as insoluble as Int ~ Bool.

Exactly the same is true if we have [G] Int ~ Bool, [W] Int ~ Bool.

Conclusion: if there's an insoluble constraint (isInsolubleReason),
then report it directly, not in the "cannot deduce X from Y" form.
This is done in misMatchOrCND (via the insoluble_occurs_check arg)

(NB: there are potentially-soluble ones, like (a ~ F a b), and we don't
want to be as draconian with them.)
-}

sameOccExtras :: TcType -> TcType -> Maybe SameOccInfo
-- See Note [Disambiguating (X ~ X) errors]
sameOccExtras :: Type -> Type -> Maybe SameOccInfo
sameOccExtras Type
ty1 Type
ty2
  | Just (TyCon
tc1, [Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty1
  , Just (TyCon
tc2, [Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty2
  , let n1 :: Name
n1 = TyCon -> Name
tyConName TyCon
tc1
        n2 :: Name
n2 = TyCon -> Name
tyConName TyCon
tc2
        same_occ :: Bool
same_occ = Name -> OccName
nameOccName Name
n1                   OccName -> OccName -> Bool
forall a. Eq a => a -> a -> Bool
== Name -> OccName
nameOccName Name
n2
        same_pkg :: Bool
same_pkg = GenModule Unit -> Unit
forall unit. GenModule unit -> unit
moduleUnit (HasDebugCallStack => Name -> GenModule Unit
Name -> GenModule Unit
nameModule Name
n1) Unit -> Unit -> Bool
forall a. Eq a => a -> a -> Bool
== GenModule Unit -> Unit
forall unit. GenModule unit -> unit
moduleUnit (HasDebugCallStack => Name -> GenModule Unit
Name -> GenModule Unit
nameModule Name
n2)
  , Name
n1 Name -> Name -> Bool
forall a. Eq a => a -> a -> Bool
/= Name
n2   -- Different Names
  , Bool
same_occ   -- but same OccName
  = SameOccInfo -> Maybe SameOccInfo
forall a. a -> Maybe a
Just (SameOccInfo -> Maybe SameOccInfo)
-> SameOccInfo -> Maybe SameOccInfo
forall a b. (a -> b) -> a -> b
$ Bool -> Name -> Name -> SameOccInfo
SameOcc Bool
same_pkg Name
n1 Name
n2
  | Bool
otherwise
  = Maybe SameOccInfo
forall a. Maybe a
Nothing

{- Note [Disambiguating (X ~ X) errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See #8278

Note [Reporting occurs-check errors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Given (a ~ [a]), if 'a' is a rigid type variable bound by a user-supplied
type signature, then the best thing is to report that we can't unify
a with [a], because a is a skolem variable.  That avoids the confusing
"occur-check" error message.

But nowadays when inferring the type of a function with no type signature,
even if there are errors inside, we still generalise its signature and
carry on. For example
   f x = x:x
Here we will infer something like
   f :: forall a. a -> [a]
with a deferred error of (a ~ [a]).  So in the deferred unsolved constraint
'a' is now a skolem, but not one bound by the programmer in the context!
Here we really should report an occurs check.

So isUserSkolem distinguishes the two.

Note [Non-injective type functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's very confusing to get a message like
     Couldn't match expected type `Depend s'
            against inferred type `Depend s1'
so mkTyFunInfoMsg adds:
       NB: `Depend' is type function, and hence may not be injective

Warn of loopy local equalities that were dropped.


************************************************************************
*                                                                      *
                 Type-class errors
*                                                                      *
************************************************************************
-}

mkDictErr :: HasDebugCallStack => SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkDictErr :: HasDebugCallStack =>
SolverReportErrCtxt -> NonEmpty ErrorItem -> TcM SolverReport
mkDictErr SolverReportErrCtxt
ctxt NonEmpty ErrorItem
orig_items
  = do { inst_envs <- TcM InstEnvs
tcGetInstEnvs
       ; let min_items = NonEmpty ErrorItem -> [ErrorItem]
elim_superclasses NonEmpty ErrorItem
items
             lookups = (ErrorItem -> (ErrorItem, ClsInstLookupResult))
-> [ErrorItem] -> [(ErrorItem, ClsInstLookupResult)]
forall a b. (a -> b) -> [a] -> [b]
map (InstEnvs -> ErrorItem -> (ErrorItem, ClsInstLookupResult)
lookup_cls_inst InstEnvs
inst_envs) [ErrorItem]
min_items
             (no_inst_items, overlap_items) = partition is_no_inst lookups

       -- Report definite no-instance errors,
       -- or (iff there are none) overlap errors
       -- But we report only one of them (hence 'head') because they all
       -- have the same source-location origin, to try avoid a cascade
       -- of error from one location
       ; err <- mk_dict_err ctxt (head (no_inst_items ++ overlap_items))
       ; return $ important ctxt err }
  where
    items :: NonEmpty ErrorItem
items = (ErrorItem -> Bool) -> NonEmpty ErrorItem -> NonEmpty ErrorItem
forall a. (a -> Bool) -> NonEmpty a -> NonEmpty a
tryFilter (Bool -> Bool
not (Bool -> Bool) -> (ErrorItem -> Bool) -> ErrorItem -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. ErrorItem -> Bool
ei_suppress) NonEmpty ErrorItem
orig_items

    no_givens :: Bool
no_givens = [Implication] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null (SolverReportErrCtxt -> [Implication]
getUserGivens SolverReportErrCtxt
ctxt)

    is_no_inst :: (ErrorItem, ClsInstLookupResult) -> Bool
is_no_inst (ErrorItem
item, ([InstMatch]
matches, PotentialUnifiers
unifiers, [InstMatch]
_))
      =  Bool
no_givens
      Bool -> Bool -> Bool
&& [InstMatch] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [InstMatch]
matches
      Bool -> Bool -> Bool
&& (PotentialUnifiers -> Bool
nullUnifiers PotentialUnifiers
unifiers Bool -> Bool -> Bool
|| (TcId -> Bool) -> [TcId] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all (Bool -> Bool
not (Bool -> Bool) -> (TcId -> Bool) -> TcId -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TcId -> Bool
isAmbiguousTyVar) (Type -> [TcId]
tyCoVarsOfTypeList (ErrorItem -> Type
errorItemPred ErrorItem
item)))

    lookup_cls_inst :: InstEnvs -> ErrorItem -> (ErrorItem, ClsInstLookupResult)
lookup_cls_inst InstEnvs
inst_envs ErrorItem
item
      = (ErrorItem
item, Bool -> InstEnvs -> Class -> [Type] -> ClsInstLookupResult
lookupInstEnv Bool
True InstEnvs
inst_envs Class
clas [Type]
tys)
      where
        (Class
clas, [Type]
tys) = HasDebugCallStack => Type -> (Class, [Type])
Type -> (Class, [Type])
getClassPredTys (ErrorItem -> Type
errorItemPred ErrorItem
item)


    -- When simplifying [W] Ord (Set a), we need
    --    [W] Eq a, [W] Ord a
    -- but we really only want to report the latter
    elim_superclasses :: NonEmpty ErrorItem -> [ErrorItem]
elim_superclasses = (ErrorItem -> Type) -> [ErrorItem] -> [ErrorItem]
forall a. (a -> Type) -> [a] -> [a]
mkMinimalBySCs ErrorItem -> Type
errorItemPred ([ErrorItem] -> [ErrorItem])
-> (NonEmpty ErrorItem -> [ErrorItem])
-> NonEmpty ErrorItem
-> [ErrorItem]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. NonEmpty ErrorItem -> [ErrorItem]
forall a. NonEmpty a -> [a]
forall (t :: * -> *) a. Foldable t => t a -> [a]
toList

-- Note [mk_dict_err]
-- ~~~~~~~~~~~~~~~~~~~
-- Different dictionary error messages are reported depending on the number of
-- matches and unifiers:
--
--   - No matches, regardless of unifiers: report "No instance for ...".
--   - Two or more matches, regardless of unifiers: report "Overlapping instances for ...",
--     and show the matching and unifying instances.
--   - One match, one or more unifiers: report "Overlapping instances for", show the
--     matching and unifying instances, and say "The choice depends on the instantion of ...,
--     and the result of evaluating ...".
mk_dict_err :: HasCallStack => SolverReportErrCtxt -> (ErrorItem, ClsInstLookupResult)
            -> TcM TcSolverReportMsg
mk_dict_err :: HasCallStack =>
SolverReportErrCtxt
-> (ErrorItem, ClsInstLookupResult) -> TcM TcSolverReportMsg
mk_dict_err SolverReportErrCtxt
ctxt (ErrorItem
item, ([InstMatch]
matches, PotentialUnifiers
unifiers, [InstMatch]
unsafe_overlapped)) = case ([InstMatch] -> Maybe (NonEmpty InstMatch)
forall a. [a] -> Maybe (NonEmpty a)
NE.nonEmpty [InstMatch]
matches, [InstMatch] -> Maybe (NonEmpty InstMatch)
forall a. [a] -> Maybe (NonEmpty a)
NE.nonEmpty [InstMatch]
unsafe_overlapped) of
  (Maybe (NonEmpty InstMatch)
Nothing, Maybe (NonEmpty InstMatch)
_)  -> do -- No matches but perhaps several unifiers
    { (_, rel_binds, item) <- Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
True SolverReportErrCtxt
ctxt ErrorItem
item
    ; candidate_insts <- get_candidate_instances
    ; (imp_errs, field_suggestions) <- record_field_suggestions item
    ; return (cannot_resolve_msg item candidate_insts rel_binds imp_errs field_suggestions) }

  -- Some matches => overlap errors
  (Just NonEmpty InstMatch
matchesNE, Maybe (NonEmpty InstMatch)
Nothing) -> TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (TcSolverReportMsg -> TcM TcSolverReportMsg)
-> TcSolverReportMsg -> TcM TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$
    ErrorItem -> NonEmpty ClsInst -> [ClsInst] -> TcSolverReportMsg
OverlappingInstances ErrorItem
item ((InstMatch -> ClsInst) -> NonEmpty InstMatch -> NonEmpty ClsInst
forall a b. (a -> b) -> NonEmpty a -> NonEmpty b
NE.map InstMatch -> ClsInst
forall a b. (a, b) -> a
fst NonEmpty InstMatch
matchesNE) (PotentialUnifiers -> [ClsInst]
getPotentialUnifiers PotentialUnifiers
unifiers)

  (Just (InstMatch
match :| []), Just NonEmpty InstMatch
unsafe_overlappedNE) -> TcSolverReportMsg -> TcM TcSolverReportMsg
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (TcSolverReportMsg -> TcM TcSolverReportMsg)
-> TcSolverReportMsg -> TcM TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$
    ErrorItem -> ClsInst -> NonEmpty ClsInst -> TcSolverReportMsg
UnsafeOverlap ErrorItem
item (InstMatch -> ClsInst
forall a b. (a, b) -> a
fst InstMatch
match) ((InstMatch -> ClsInst) -> NonEmpty InstMatch -> NonEmpty ClsInst
forall a b. (a -> b) -> NonEmpty a -> NonEmpty b
NE.map InstMatch -> ClsInst
forall a b. (a, b) -> a
fst NonEmpty InstMatch
unsafe_overlappedNE)
  (Just matches :: NonEmpty InstMatch
matches@(InstMatch
_ :| [InstMatch]
_), Just NonEmpty InstMatch
overlaps) -> String -> SDoc -> TcM TcSolverReportMsg
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"mk_dict_err: multiple matches with overlap" (SDoc -> TcM TcSolverReportMsg) -> SDoc -> TcM TcSolverReportMsg
forall a b. (a -> b) -> a -> b
$ [SDoc] -> SDoc
forall doc. IsDoc doc => [doc] -> doc
vcat [ String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"matches:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> NonEmpty InstMatch -> SDoc
forall a. Outputable a => a -> SDoc
ppr NonEmpty InstMatch
matches, String -> SDoc
forall doc. IsLine doc => String -> doc
text String
"overlaps:" SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> NonEmpty InstMatch -> SDoc
forall a. Outputable a => a -> SDoc
ppr NonEmpty InstMatch
overlaps ]
  where
    orig :: CtOrigin
orig          = ErrorItem -> CtOrigin
errorItemOrigin ErrorItem
item
    pred :: Type
pred          = ErrorItem -> Type
errorItemPred ErrorItem
item
    (Class
clas, [Type]
tys)   = HasDebugCallStack => Type -> (Class, [Type])
Type -> (Class, [Type])
getClassPredTys Type
pred

    get_candidate_instances :: TcM [ClsInst]
    -- See Note [Report candidate instances]
    get_candidate_instances :: TcM [ClsInst]
get_candidate_instances
      | [Type
ty] <- [Type]
tys   -- Only try for single-parameter classes
      = do { instEnvs <- TcM InstEnvs
tcGetInstEnvs
           ; return (filter (is_candidate_inst ty)
                            (classInstances instEnvs clas)) }
      | Bool
otherwise = [ClsInst] -> TcM [ClsInst]
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return []

    is_candidate_inst :: Type -> ClsInst -> Bool
is_candidate_inst Type
ty ClsInst
inst -- See Note [Report candidate instances]
      | [Type
other_ty] <- ClsInst -> [Type]
is_tys ClsInst
inst
      , Just (TyCon
tc1, [Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
ty
      , Just (TyCon
tc2, [Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
other_ty
      = let n1 :: Name
n1 = TyCon -> Name
tyConName TyCon
tc1
            n2 :: Name
n2 = TyCon -> Name
tyConName TyCon
tc2
            different_names :: Bool
different_names = Name
n1 Name -> Name -> Bool
forall a. Eq a => a -> a -> Bool
/= Name
n2
            same_occ_names :: Bool
same_occ_names = Name -> OccName
nameOccName Name
n1 OccName -> OccName -> Bool
forall a. Eq a => a -> a -> Bool
== Name -> OccName
nameOccName Name
n2
        in Bool
different_names Bool -> Bool -> Bool
&& Bool
same_occ_names
      | Bool
otherwise = Bool
False

    -- See Note [Out-of-scope fields with -XOverloadedRecordDot]
    record_field_suggestions :: ErrorItem -> TcM ([ImportError], [GhcHint])
    record_field_suggestions :: ErrorItem -> RnM ([ImportError], [GhcHint])
record_field_suggestions ErrorItem
item = ((OccName -> RnM ([ImportError], [GhcHint]))
 -> Maybe OccName -> RnM ([ImportError], [GhcHint]))
-> Maybe OccName
-> (OccName -> RnM ([ImportError], [GhcHint]))
-> RnM ([ImportError], [GhcHint])
forall a b c. (a -> b -> c) -> b -> a -> c
flip (RnM ([ImportError], [GhcHint])
-> (OccName -> RnM ([ImportError], [GhcHint]))
-> Maybe OccName
-> RnM ([ImportError], [GhcHint])
forall b a. b -> (a -> b) -> Maybe a -> b
maybe (RnM ([ImportError], [GhcHint])
 -> (OccName -> RnM ([ImportError], [GhcHint]))
 -> Maybe OccName
 -> RnM ([ImportError], [GhcHint]))
-> RnM ([ImportError], [GhcHint])
-> (OccName -> RnM ([ImportError], [GhcHint]))
-> Maybe OccName
-> RnM ([ImportError], [GhcHint])
forall a b. (a -> b) -> a -> b
$ ([ImportError], [GhcHint]) -> RnM ([ImportError], [GhcHint])
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return ([], [GhcHint]
noHints)) Maybe OccName
record_field ((OccName -> RnM ([ImportError], [GhcHint]))
 -> RnM ([ImportError], [GhcHint]))
-> (OccName -> RnM ([ImportError], [GhcHint]))
-> RnM ([ImportError], [GhcHint])
forall a b. (a -> b) -> a -> b
$ \OccName
name ->
       do { glb_env <- TcRn GlobalRdrEnv
getGlobalRdrEnv
          ; lcl_env <- getLocalRdrEnv
          ; let field_name_hints = ErrorItem -> [GhcHint]
report_no_fieldnames ErrorItem
item
          ; (errs, hints) <- if occ_name_in_scope glb_env lcl_env name
              then return ([], noHints)
              else unknownNameSuggestions emptyLocalRdrEnv WL_RecField (mkRdrUnqual name)
          ; pure (errs, hints ++ field_name_hints)
          }

    -- get type names from instance
    -- resolve the type - if it's in scope is it a record?
    -- if it's a record, report an error - the record name + the field that could not be found
    report_no_fieldnames :: ErrorItem -> [GhcHint]
    report_no_fieldnames :: ErrorItem -> [GhcHint]
report_no_fieldnames ErrorItem
item
       | Just (EvVarDest TcId
evvar) <- ErrorItem -> Maybe TcEvDest
ei_evdest ErrorItem
item
       -- we can assume that here we have a `HasField @Symbol x r a` instance
       -- because of HasFieldOrigin in record_field
       , Just (TyCon
_, [Type
_symbol, Type
x, Type
r, Type
a]) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe (TcId -> Type
varType TcId
evvar)
       , Just (TyCon
r_tycon, [Type]
_) <- HasCallStack => Type -> Maybe (TyCon, [Type])
Type -> Maybe (TyCon, [Type])
tcSplitTyConApp_maybe Type
r
       , Just FastString
x_name <- Type -> Maybe FastString
isStrLitTy Type
x
       -- we check that this is a record type by checking whether it has any
       -- fields (in scope)
       , Bool -> Bool
not (Bool -> Bool) -> ([FieldLabel] -> Bool) -> [FieldLabel] -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. [FieldLabel] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null ([FieldLabel] -> Bool) -> [FieldLabel] -> Bool
forall a b. (a -> b) -> a -> b
$ TyCon -> [FieldLabel]
tyConFieldLabels TyCon
r_tycon
       = [FastString -> Type -> Type -> GhcHint
RemindRecordMissingField FastString
x_name Type
r Type
a]
       | Bool
otherwise = []

    occ_name_in_scope :: GlobalRdrEnv -> LocalRdrEnv -> OccName -> Bool
occ_name_in_scope GlobalRdrEnv
glb_env LocalRdrEnv
lcl_env OccName
occ_name = Bool -> Bool
not (Bool -> Bool) -> Bool -> Bool
forall a b. (a -> b) -> a -> b
$
      [GlobalRdrEltX GREInfo] -> Bool
forall a. [a] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null (GlobalRdrEnv -> LookupGRE GREInfo -> [GlobalRdrEltX GREInfo]
forall info.
GlobalRdrEnvX info -> LookupGRE info -> [GlobalRdrEltX info]
lookupGRE GlobalRdrEnv
glb_env (OccName -> WhichGREs GREInfo -> LookupGRE GREInfo
forall info. OccName -> WhichGREs info -> LookupGRE info
LookupOccName OccName
occ_name (FieldsOrSelectors -> WhichGREs GREInfo
RelevantGREsFOS FieldsOrSelectors
WantNormal))) Bool -> Bool -> Bool
&&
      Maybe Name -> Bool
forall a. Maybe a -> Bool
isNothing (LocalRdrEnv -> OccName -> Maybe Name
lookupLocalRdrOcc LocalRdrEnv
lcl_env OccName
occ_name)

    record_field :: Maybe OccName
record_field = case CtOrigin
orig of
      HasFieldOrigin FastString
name -> OccName -> Maybe OccName
forall a. a -> Maybe a
Just (FastString -> OccName
mkVarOccFS FastString
name)
      CtOrigin
_                   -> Maybe OccName
forall a. Maybe a
Nothing

    cannot_resolve_msg :: ErrorItem -> [ClsInst] -> RelevantBindings
                       -> [ImportError] -> [GhcHint] -> TcSolverReportMsg
    cannot_resolve_msg :: ErrorItem
-> [ClsInst]
-> RelevantBindings
-> [ImportError]
-> [GhcHint]
-> TcSolverReportMsg
cannot_resolve_msg ErrorItem
item [ClsInst]
candidate_insts RelevantBindings
binds [ImportError]
imp_errs [GhcHint]
field_suggestions
      = ErrorItem
-> [ClsInst]
-> [ClsInst]
-> [ImportError]
-> [GhcHint]
-> RelevantBindings
-> TcSolverReportMsg
CannotResolveInstance ErrorItem
item (PotentialUnifiers -> [ClsInst]
getPotentialUnifiers PotentialUnifiers
unifiers) [ClsInst]
candidate_insts [ImportError]
imp_errs [GhcHint]
field_suggestions RelevantBindings
binds

{- Note [Report candidate instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we have an unsolved (Num Int), where `Int` is not the Prelude Int,
but comes from some other module, then it may be helpful to point out
that there are some similarly named instances elsewhere.  So we get
something like
    No instance for (Num Int) arising from the literal ‘3’
    There are instances for similar types:
      instance Num GHC.Types.Int -- Defined in ‘GHC.Num’
Discussion in #9611.

Note [Highlighting ambiguous type variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we encounter ambiguous type variables (i.e. type variables
that remain metavariables after type inference), we need a few more
conditions before we can reason that *ambiguity* prevents constraints
from being solved:
  - We can't have any givens, as encountering a typeclass error
    with given constraints just means we couldn't deduce
    a solution satisfying those constraints and as such couldn't
    bind the type variable to a known type.
  - If we don't have any unifiers, we don't even have potential
    instances from which an ambiguity could arise.
  - Lastly, I don't want to mess with error reporting for
    unknown runtime types so we just fall back to the old message there.
Once these conditions are satisfied, we can safely say that ambiguity prevents
the constraint from being solved.

Note [Out-of-scope fields with -XOverloadedRecordDot]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With -XOverloadedRecordDot, when a field isn't in scope, the error that appears
is produces here, and it says
    No instance for (GHC.Record.HasField "<fieldname>" ...).

Additionally, though, we want to suggest similar field names that are in scope
or could be in scope with different import lists.

However, we can still get an error about a missing HasField instance when a
field is in scope (if the types are wrong), and so it's important that we don't
suggest similar names here if the record field is in scope, either qualified or
unqualified, since qualification doesn't matter for -XOverloadedRecordDot.

Example:

    import Data.Monoid (Alt(..))

    foo = undefined.getAll

results in

     No instance for (GHC.Records.HasField "getAll" r0 a0)
        arising from selecting the field ‘getAll’
      Perhaps you meant ‘getAlt’ (imported from Data.Monoid)
      Perhaps you want to add ‘getAll’ to the import list
      in the import of ‘Data.Monoid’
-}

{-
Note [Kind arguments in error messages]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It can be terribly confusing to get an error message like (#9171)

    Couldn't match expected type ‘GetParam Base (GetParam Base Int)’
                with actual type ‘GetParam Base (GetParam Base Int)’

The reason may be that the kinds don't match up.  Typically you'll get
more useful information, but not when it's as a result of ambiguity.

To mitigate this, GHC attempts to enable the -fprint-explicit-kinds flag
whenever any error message arises due to a kind mismatch. This means that
the above error message would instead be displayed as:

    Couldn't match expected type
                  ‘GetParam @* @k2 @* Base (GetParam @* @* @k2 Base Int)’
                with actual type
                  ‘GetParam @* @k20 @* Base (GetParam @* @* @k20 Base Int)’

Which makes it clearer that the culprit is the mismatch between `k2` and `k20`.
-}

-----------------------
-- relevantBindings looks at the value environment and finds values whose
-- types mention any of the offending type variables.  It has to be
-- careful to zonk the Id's type first, so it has to be in the monad.
-- We must be careful to pass it a zonked type variable, too.
--
-- We always remove closed top-level bindings, though,
-- since they are never relevant (cf #8233)

relevantBindings :: Bool  -- True <=> filter by tyvar; False <=> no filtering
                          -- See #8191
                 -> SolverReportErrCtxt -> ErrorItem
                 -> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
-- Also returns the zonked and tidied CtOrigin of the constraint
relevantBindings :: Bool
-> SolverReportErrCtxt
-> ErrorItem
-> TcM (SolverReportErrCtxt, RelevantBindings, ErrorItem)
relevantBindings Bool
want_filtering SolverReportErrCtxt
ctxt ErrorItem
item
  = do { String -> SDoc -> TcM ()
traceTc String
"relevantBindings" (ErrorItem -> SDoc
forall a. Outputable a => a -> SDoc
ppr ErrorItem
item)
       ; (env1, tidy_orig) <- ZonkM (TidyEnv, CtOrigin) -> TcM (TidyEnv, CtOrigin)
forall a. ZonkM a -> TcM a
liftZonkM (ZonkM (TidyEnv, CtOrigin) -> TcM (TidyEnv, CtOrigin))
-> ZonkM (TidyEnv, CtOrigin) -> TcM (TidyEnv, CtOrigin)
forall a b. (a -> b) -> a -> b
$ TidyEnv -> CtOrigin -> ZonkM (TidyEnv, CtOrigin)
zonkTidyOrigin (SolverReportErrCtxt -> TidyEnv
cec_tidy SolverReportErrCtxt
ctxt) (CtLoc -> CtOrigin
ctLocOrigin CtLoc
loc)

             -- For *kind* errors, report the relevant bindings of the
             -- enclosing *type* equality, because that's more useful for the programmer
       ; let extra_tvs = case CtOrigin
tidy_orig of
                             KindEqOrigin Type
t1 Type
t2 CtOrigin
_ Maybe TypeOrKind
_ -> [Type] -> TyCoVarSet
tyCoVarsOfTypes [Type
t1,Type
t2]
                             CtOrigin
_                      -> TyCoVarSet
emptyVarSet
             ct_fvs = Type -> TyCoVarSet
tyCoVarsOfType (ErrorItem -> Type
errorItemPred ErrorItem
item) TyCoVarSet -> TyCoVarSet -> TyCoVarSet
`unionVarSet` TyCoVarSet
extra_tvs

             -- Put a zonked, tidied CtOrigin into the ErrorItem
             loc'   = CtLoc -> CtOrigin -> CtLoc
setCtLocOrigin CtLoc
loc CtOrigin
tidy_orig
             item'  = ErrorItem
item { ei_loc = loc' }

       ; (env2, lcl_name_cache) <- liftZonkM $ zonkTidyTcLclEnvs env1 [lcl_env]

       ; relev_bds <- relevant_bindings want_filtering lcl_env lcl_name_cache ct_fvs
       ; let ctxt'  = SolverReportErrCtxt
ctxt { cec_tidy = env2 }
       ; return (ctxt', relev_bds, item') }
  where
    loc :: CtLoc
loc     = ErrorItem -> CtLoc
errorItemCtLoc ErrorItem
item
    lcl_env :: CtLocEnv
lcl_env = CtLoc -> CtLocEnv
ctLocEnv CtLoc
loc

-- slightly more general version, to work also with holes
relevant_bindings :: Bool
                  -> CtLocEnv
                  -> NameEnv Type -- Cache of already zonked and tidied types
                  -> TyCoVarSet
                  -> TcM RelevantBindings
relevant_bindings :: Bool
-> CtLocEnv -> NameEnv Type -> TyCoVarSet -> TcM RelevantBindings
relevant_bindings Bool
want_filtering CtLocEnv
lcl_env NameEnv Type
lcl_name_env TyCoVarSet
ct_tvs
  = do { dflags <- IOEnv (Env TcGblEnv TcLclEnv) DynFlags
forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
       ; traceTc "relevant_bindings" $
           vcat [ ppr ct_tvs
                , pprWithCommas id [ ppr id <+> dcolon <+> ppr (idType id)
                                   | TcIdBndr id _ <- ctl_bndrs lcl_env ]
                , pprWithCommas id
                    [ ppr id | TcIdBndr_ExpType id _ _ <- ctl_bndrs lcl_env ] ]

       ; go dflags (maxRelevantBinds dflags)
                    emptyVarSet (RelevantBindings [] False)
                    (removeBindingShadowing $ ctl_bndrs lcl_env)
         -- tcl_bndrs has the innermost bindings first,
         -- which are probably the most relevant ones
  }
  where
    run_out :: Maybe Int -> Bool
    run_out :: Maybe Int -> Bool
run_out Maybe Int
Nothing = Bool
False
    run_out (Just Int
n) = Int
n Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
<= Int
0

    dec_max :: Maybe Int -> Maybe Int
    dec_max :: Maybe Int -> Maybe Int
dec_max = (Int -> Int) -> Maybe Int -> Maybe Int
forall a b. (a -> b) -> Maybe a -> Maybe b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (\Int
n -> Int
n Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1)


    go :: DynFlags -> Maybe Int -> TcTyVarSet
       -> RelevantBindings
       -> [TcBinder]
       -> TcM RelevantBindings
    go :: DynFlags
-> Maybe Int
-> TyCoVarSet
-> RelevantBindings
-> [TcBinder]
-> TcM RelevantBindings
go DynFlags
_ Maybe Int
_ TyCoVarSet
_ (RelevantBindings [(Name, Type)]
bds Bool
discards) []
      = RelevantBindings -> TcM RelevantBindings
forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. Monad m => a -> m a
return (RelevantBindings -> TcM RelevantBindings)
-> RelevantBindings -> TcM RelevantBindings
forall a b. (a -> b) -> a -> b
$ [(Name, Type)] -> Bool -> RelevantBindings
RelevantBindings ([(Name, Type)] -> [(Name, Type)]
forall a. [a] -> [a]
reverse [(Name, Type)]
bds) Bool
discards
    go DynFlags
dflags Maybe Int
n_left TyCoVarSet
tvs_seen rels :: RelevantBindings
rels@(RelevantBindings [(Name, Type)]
bds Bool
discards) (TcBinder
tc_bndr : [TcBinder]
tc_bndrs)
      = case TcBinder
tc_bndr of
          TcTvBndr {} -> TcM RelevantBindings
discard_it
          TcIdBndr TcId
id TopLevelFlag
top_lvl -> Name -> TopLevelFlag -> TcM RelevantBindings
go2 (TcId -> Name
idName TcId
id) TopLevelFlag
top_lvl
          TcIdBndr_ExpType Name
name ExpType
et TopLevelFlag
top_lvl ->
            do { mb_ty <- IO (Maybe Type) -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe Type)
forall a. IO a -> IOEnv (Env TcGblEnv TcLclEnv) a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (IO (Maybe Type) -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe Type))
-> IO (Maybe Type) -> IOEnv (Env TcGblEnv TcLclEnv) (Maybe Type)
forall a b. (a -> b) -> a -> b
$ ExpType -> IO (Maybe Type)
forall (m :: * -> *). MonadIO m => ExpType -> m (Maybe Type)
readExpType_maybe ExpType
et
                   -- et really should be filled in by now. But there's a chance
                   -- it hasn't, if, say, we're reporting a kind error en route to
                   -- checking a term. See test indexed-types/should_fail/T8129
                   -- Or we are reporting errors from the ambiguity check on
                   -- a local type signature
               ; case mb_ty of
                   Just Type
_ty -> Name -> TopLevelFlag -> TcM RelevantBindings
go2 Name
name TopLevelFlag
top_lvl
                   Maybe Type
Nothing -> TcM RelevantBindings
discard_it  -- No info; discard
               }
      where
        discard_it :: TcM RelevantBindings
discard_it = DynFlags
-> Maybe Int
-> TyCoVarSet
-> RelevantBindings
-> [TcBinder]
-> TcM RelevantBindings
go DynFlags
dflags Maybe Int
n_left TyCoVarSet
tvs_seen RelevantBindings
rels [TcBinder]
tc_bndrs
        go2 :: Name -> TopLevelFlag -> TcM RelevantBindings
go2 Name
id_name TopLevelFlag
top_lvl
          = do { let tidy_ty :: Type
tidy_ty = case NameEnv Type -> Name -> Maybe Type
forall a. NameEnv a -> Name -> Maybe a
lookupNameEnv NameEnv Type
lcl_name_env Name
id_name of
                                  Just Type
tty -> Type
tty
                                  Maybe Type
Nothing -> String -> SDoc -> Type
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"relevant_bindings" (Name -> SDoc
forall a. Outputable a => a -> SDoc
ppr Name
id_name)
               ; String -> SDoc -> TcM ()
traceTc String
"relevantBindings 1" (Name -> SDoc
forall a. Outputable a => a -> SDoc
ppr Name
id_name SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> SDoc
dcolon SDoc -> SDoc -> SDoc
forall doc. IsLine doc => doc -> doc -> doc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
tidy_ty)
               ; let id_tvs :: TyCoVarSet
id_tvs = Type -> TyCoVarSet
tyCoVarsOfType Type
tidy_ty
                     bd :: (Name, Type)
bd = (Name
id_name, Type
tidy_ty)
                     new_seen :: TyCoVarSet
new_seen = TyCoVarSet
tvs_seen TyCoVarSet -> TyCoVarSet -> TyCoVarSet
`unionVarSet` TyCoVarSet
id_tvs

               ; if (Bool
want_filtering Bool -> Bool -> Bool
&& Bool -> Bool
not (DynFlags -> Bool
hasPprDebug DynFlags
dflags)
                                    Bool -> Bool -> Bool
&& TyCoVarSet
id_tvs TyCoVarSet -> TyCoVarSet -> Bool
`disjointVarSet` TyCoVarSet
ct_tvs)
                          -- We want to filter out this binding anyway
                          -- so discard it silently
                 then TcM RelevantBindings
discard_it

                 else if TopLevelFlag -> Bool
isTopLevel TopLevelFlag
top_lvl Bool -> Bool -> Bool
&& Bool -> Bool
not (Maybe Int -> Bool
forall a. Maybe a -> Bool
isNothing Maybe Int
n_left)
                          -- It's a top-level binding and we have not specified
                          -- -fno-max-relevant-bindings, so discard it silently
                 then TcM RelevantBindings
discard_it

                 else if Maybe Int -> Bool
run_out Maybe Int
n_left Bool -> Bool -> Bool
&& TyCoVarSet
id_tvs TyCoVarSet -> TyCoVarSet -> Bool
`subVarSet` TyCoVarSet
tvs_seen
                          -- We've run out of n_left fuel and this binding only
                          -- mentions already-seen type variables, so discard it
                 then DynFlags
-> Maybe Int
-> TyCoVarSet
-> RelevantBindings
-> [TcBinder]
-> TcM RelevantBindings
go DynFlags
dflags Maybe Int
n_left TyCoVarSet
tvs_seen ([(Name, Type)] -> Bool -> RelevantBindings
RelevantBindings [(Name, Type)]
bds Bool
True) -- Record that we have now discarded something
                         [TcBinder]
tc_bndrs

                          -- Keep this binding, decrement fuel
                 else DynFlags
-> Maybe Int
-> TyCoVarSet
-> RelevantBindings
-> [TcBinder]
-> TcM RelevantBindings
go DynFlags
dflags (Maybe Int -> Maybe Int
dec_max Maybe Int
n_left) TyCoVarSet
new_seen
                         ([(Name, Type)] -> Bool -> RelevantBindings
RelevantBindings ((Name, Type)
bd(Name, Type) -> [(Name, Type)] -> [(Name, Type)]
forall a. a -> [a] -> [a]
:[(Name, Type)]
bds) Bool
discards) [TcBinder]
tc_bndrs }

-----------------------
warnDefaulting :: [Ct] -> TcTyVar -> Type -> TcM ()
warnDefaulting :: [Ct] -> TcId -> Type -> TcM ()
warnDefaulting [] TcId
_ Type
_
  = String -> TcM ()
forall a. HasCallStack => String -> a
panic String
"warnDefaulting: empty Wanteds"
warnDefaulting wanteds :: [Ct]
wanteds@(Ct
ct:[Ct]
_) TcId
the_tv Type
default_ty
  = do { warn_default <- WarningFlag -> TcRnIf TcGblEnv TcLclEnv Bool
forall gbl lcl. WarningFlag -> TcRnIf gbl lcl Bool
woptM WarningFlag
Opt_WarnTypeDefaults
       ; env0 <- liftZonkM $ tcInitTidyEnv
            -- don't want to report all the superclass constraints, which
            -- add unhelpful clutter
       ; let filtered = (Ct -> Bool) -> [Ct] -> [Ct]
forall a. (a -> Bool) -> [a] -> [a]
filter (Bool -> Bool
not (Bool -> Bool) -> (Ct -> Bool) -> Ct -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. CtOrigin -> Bool
isWantedSuperclassOrigin (CtOrigin -> Bool) -> (Ct -> CtOrigin) -> Ct -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Ct -> CtOrigin
ctOrigin) [Ct]
wanteds
             tidy_env = TidyEnv -> [TcId] -> TidyEnv
tidyFreeTyCoVars TidyEnv
env0 ([TcId] -> TidyEnv) -> [TcId] -> TidyEnv
forall a b. (a -> b) -> a -> b
$
                        Cts -> [TcId]
tyCoVarsOfCtsList ([Ct] -> Cts
forall a. [a] -> Bag a
listToBag [Ct]
filtered)
             tidy_wanteds = (Ct -> Ct) -> [Ct] -> [Ct]
forall a b. (a -> b) -> [a] -> [b]
map (TidyEnv -> Ct -> Ct
tidyCt TidyEnv
tidy_env) [Ct]
filtered
             tidy_tv = UniqFM TcId TcId -> TcId -> Maybe TcId
forall a. VarEnv a -> TcId -> Maybe a
lookupVarEnv (TidyEnv -> UniqFM TcId TcId
forall a b. (a, b) -> b
snd TidyEnv
tidy_env) TcId
the_tv
             diag = [Ct] -> Maybe TcId -> Type -> TcRnMessage
TcRnWarnDefaulting [Ct]
tidy_wanteds Maybe TcId
tidy_tv Type
default_ty
             loc = Ct -> CtLoc
ctLoc Ct
ct
       ; setCtLocM loc $ diagnosticTc warn_default diag }

{-
Note [Runtime skolems]
~~~~~~~~~~~~~~~~~~~~~~
We want to give a reasonably helpful error message for ambiguity
arising from *runtime* skolems in the debugger.  These
are created by in GHC.Runtime.Heap.Inspect.zonkRTTIType.
-}

{-**********************************************************************
*                                                                      *
                      GHC API helper functions
*                                                                      *
**********************************************************************-}

-- | If the 'TcSolverReportMsg' is a type mismatch between
-- an actual and an expected type, return the actual and expected types
-- (in that order).
--
-- Prefer using this over manually inspecting the 'TcSolverReportMsg' datatype
-- if you just want this information, as the datatype itself is subject to change
-- across GHC versions.
solverReportMsg_ExpectedActuals :: TcSolverReportMsg -> Maybe (Type, Type)
solverReportMsg_ExpectedActuals :: TcSolverReportMsg -> Maybe (Type, Type)
solverReportMsg_ExpectedActuals
  = \case
    Mismatch { mismatchMsg :: TcSolverReportMsg -> MismatchMsg
mismatchMsg = MismatchMsg
mismatch_msg } ->
      MismatchMsg -> Maybe (Type, Type)
mismatchMsg_ExpectedActuals MismatchMsg
mismatch_msg
    TcSolverReportMsg
_ -> Maybe (Type, Type)
forall a. Maybe a
Nothing

-- | Filter the list by the given predicate, but if that would be empty,
-- just give back the original list.
-- We use this as we must report something for fdefer-type-errors.
tryFilter :: (a -> Bool) -> NonEmpty a -> NonEmpty a
tryFilter :: forall a. (a -> Bool) -> NonEmpty a -> NonEmpty a
tryFilter a -> Bool
f NonEmpty a
as = NonEmpty a -> Maybe (NonEmpty a) -> NonEmpty a
forall a. a -> Maybe a -> a
fromMaybe NonEmpty a
as (Maybe (NonEmpty a) -> NonEmpty a)
-> Maybe (NonEmpty a) -> NonEmpty a
forall a b. (a -> b) -> a -> b
$ [a] -> Maybe (NonEmpty a)
forall a. [a] -> Maybe (NonEmpty a)
nonEmpty ((a -> Bool) -> [a] -> [a]
forall a. (a -> Bool) -> [a] -> [a]
filter a -> Bool
f (NonEmpty a -> [a]
forall a. NonEmpty a -> [a]
forall (t :: * -> *) a. Foldable t => t a -> [a]
toList NonEmpty a
as))