{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

-}

{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeFamilies #-}

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

-- | Typechecking instance declarations
module GHC.Tc.TyCl.Instance
   ( tcInstDecls1
   , tcInstDeclsDeriv
   , tcInstDecls2
   )
where

#include "HsVersions.h"

import GHC.Prelude

import GHC.Hs
import GHC.Tc.Gen.Bind
import GHC.Tc.TyCl
import GHC.Tc.TyCl.Utils ( addTyConsToGblEnv )
import GHC.Tc.TyCl.Class ( tcClassDecl2, tcATDefault,
                           HsSigFun, mkHsSigFun, badMethodErr,
                           findMethodBind, instantiateMethod )
import GHC.Tc.Solver( pushLevelAndSolveEqualitiesX, reportUnsolvedEqualities )
import GHC.Tc.Gen.Sig
import GHC.Tc.Utils.Monad
import GHC.Tc.Validity
import GHC.Tc.Utils.Zonk
import GHC.Tc.Utils.TcMType
import GHC.Tc.Utils.TcType
import GHC.Tc.Types.Constraint
import GHC.Tc.Types.Origin
import GHC.Tc.TyCl.Build
import GHC.Tc.Utils.Instantiate
import GHC.Tc.Instance.Class( AssocInstInfo(..), isNotAssociated )
import GHC.Core.Multiplicity
import GHC.Core.InstEnv
import GHC.Tc.Instance.Family
import GHC.Core.FamInstEnv
import GHC.Tc.Deriv
import GHC.Tc.Utils.Env
import GHC.Tc.Gen.HsType
import GHC.Tc.Utils.Unify
import GHC.Core        ( Expr(..), mkApps, mkVarApps, mkLams )
import GHC.Core.Make   ( nO_METHOD_BINDING_ERROR_ID )
import GHC.Core.Unfold.Make ( mkInlineUnfoldingWithArity, mkDFunUnfolding )
import GHC.Core.Type
import GHC.Core.SimpleOpt
import GHC.Core.Predicate( classMethodInstTy )
import GHC.Tc.Types.Evidence
import GHC.Core.TyCon
import GHC.Core.Coercion.Axiom
import GHC.Core.DataCon
import GHC.Core.ConLike
import GHC.Core.Class
import GHC.Types.Var as Var
import GHC.Types.Var.Env
import GHC.Types.Var.Set
import GHC.Data.Bag
import GHC.Types.Basic
import GHC.Types.Fixity
import GHC.Driver.Session
import GHC.Driver.Ppr
import GHC.Utils.Error
import GHC.Utils.Logger
import GHC.Data.FastString
import GHC.Types.Id
import GHC.Types.SourceText
import GHC.Data.List.SetOps
import GHC.Types.Name
import GHC.Types.Name.Set
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Types.SrcLoc
import GHC.Utils.Misc
import GHC.Data.BooleanFormula ( isUnsatisfied, pprBooleanFormulaNice )
import qualified GHC.LanguageExtensions as LangExt

import Control.Monad
import Data.Tuple
import GHC.Data.Maybe
import Data.List( mapAccumL )


{-
Typechecking instance declarations is done in two passes. The first
pass, made by @tcInstDecls1@, collects information to be used in the
second pass.

This pre-processed info includes the as-yet-unprocessed bindings
inside the instance declaration.  These are type-checked in the second
pass, when the class-instance envs and GVE contain all the info from
all the instance and value decls.  Indeed that's the reason we need
two passes over the instance decls.


Note [How instance declarations are translated]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is how we translate instance declarations into Core

Running example:
        class C a where
           op1, op2 :: Ix b => a -> b -> b
           op2 = <dm-rhs>

        instance C a => C [a]
           {-# INLINE [2] op1 #-}
           op1 = <rhs>
===>
        -- Method selectors
        op1,op2 :: forall a. C a => forall b. Ix b => a -> b -> b
        op1 = ...
        op2 = ...

        -- Default methods get the 'self' dictionary as argument
        -- so they can call other methods at the same type
        -- Default methods get the same type as their method selector
        $dmop2 :: forall a. C a => forall b. Ix b => a -> b -> b
        $dmop2 = /\a. \(d:C a). /\b. \(d2: Ix b). <dm-rhs>
               -- NB: type variables 'a' and 'b' are *both* in scope in <dm-rhs>
               -- Note [Tricky type variable scoping]

        -- A top-level definition for each instance method
        -- Here op1_i, op2_i are the "instance method Ids"
        -- The INLINE pragma comes from the user pragma
        {-# INLINE [2] op1_i #-}  -- From the instance decl bindings
        op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
        op1_i = /\a. \(d:C a).
               let this :: C [a]
                   this = df_i a d
                     -- Note [Subtle interaction of recursion and overlap]

                   local_op1 :: forall b. Ix b => [a] -> b -> b
                   local_op1 = <rhs>
                     -- Source code; run the type checker on this
                     -- NB: Type variable 'a' (but not 'b') is in scope in <rhs>
                     -- Note [Tricky type variable scoping]

               in local_op1 a d

        op2_i = /\a \d:C a. $dmop2 [a] (df_i a d)

        -- The dictionary function itself
        {-# NOINLINE CONLIKE df_i #-}   -- Never inline dictionary functions
        df_i :: forall a. C a -> C [a]
        df_i = /\a. \d:C a. MkC (op1_i a d) (op2_i a d)
                -- But see Note [Default methods in instances]
                -- We can't apply the type checker to the default-method call

        -- Use a RULE to short-circuit applications of the class ops
        {-# RULE "op1@C[a]" forall a, d:C a.
                            op1 [a] (df_i d) = op1_i a d #-}

Note [Instances and loop breakers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Note that df_i may be mutually recursive with both op1_i and op2_i.
  It's crucial that df_i is not chosen as the loop breaker, even
  though op1_i has a (user-specified) INLINE pragma.

* Instead the idea is to inline df_i into op1_i, which may then select
  methods from the MkC record, and thereby break the recursion with
  df_i, leaving a *self*-recursive op1_i.  (If op1_i doesn't call op at
  the same type, it won't mention df_i, so there won't be recursion in
  the first place.)

* If op1_i is marked INLINE by the user there's a danger that we won't
  inline df_i in it, and that in turn means that (since it'll be a
  loop-breaker because df_i isn't), op1_i will ironically never be
  inlined.  But this is OK: the recursion breaking happens by way of
  a RULE (the magic ClassOp rule above), and RULES work inside InlineRule
  unfoldings. See Note [RULEs enabled in InitialPhase] in GHC.Core.Opt.Simplify.Utils

Note [ClassOp/DFun selection]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
One thing we see a lot is stuff like
    op2 (df d1 d2)
where 'op2' is a ClassOp and 'df' is DFun.  Now, we could inline *both*
'op2' and 'df' to get
     case (MkD ($cop1 d1 d2) ($cop2 d1 d2) ... of
       MkD _ op2 _ _ _ -> op2
And that will reduce to ($cop2 d1 d2) which is what we wanted.

But it's tricky to make this work in practice, because it requires us to
inline both 'op2' and 'df'.  But neither is keen to inline without having
seen the other's result; and it's very easy to get code bloat (from the
big intermediate) if you inline a bit too much.

Instead we use a cunning trick.
 * We arrange that 'df' and 'op2' NEVER inline.

 * We arrange that 'df' is ALWAYS defined in the sylised form
      df d1 d2 = MkD ($cop1 d1 d2) ($cop2 d1 d2) ...

 * We give 'df' a magical unfolding (DFunUnfolding [$cop1, $cop2, ..])
   that lists its methods.

 * We make GHC.Core.Unfold.exprIsConApp_maybe spot a DFunUnfolding and return
   a suitable constructor application -- inlining df "on the fly" as it
   were.

 * ClassOp rules: We give the ClassOp 'op2' a BuiltinRule that
   extracts the right piece iff its argument satisfies
   exprIsConApp_maybe.  This is done in GHC.Types.Id.Make.mkDictSelId

 * We make 'df' CONLIKE, so that shared uses still match; eg
      let d = df d1 d2
      in ...(op2 d)...(op1 d)...

Note [Single-method classes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the class has just one method (or, more accurately, just one element
of {superclasses + methods}), then we use a different strategy.

   class C a where op :: a -> a
   instance C a => C [a] where op = <blah>

We translate the class decl into a newtype, which just gives a
top-level axiom. The "constructor" MkC expands to a cast, as does the
class-op selector.

   axiom Co:C a :: C a ~ (a->a)

   op :: forall a. C a -> (a -> a)
   op a d = d |> (Co:C a)

   MkC :: forall a. (a->a) -> C a
   MkC = /\a.\op. op |> (sym Co:C a)

The clever RULE stuff doesn't work now, because ($df a d) isn't
a constructor application, so exprIsConApp_maybe won't return
Just <blah>.

Instead, we simply rely on the fact that casts are cheap:

   $df :: forall a. C a => C [a]
   {-# INLINE df #-}  -- NB: INLINE this
   $df = /\a. \d. MkC [a] ($cop_list a d)
       = $cop_list |> forall a. C a -> (sym (Co:C [a]))

   $cop_list :: forall a. C a => [a] -> [a]
   $cop_list = <blah>

So if we see
   (op ($df a d))
we'll inline 'op' and '$df', since both are simply casts, and
good things happen.

Why do we use this different strategy?  Because otherwise we
end up with non-inlined dictionaries that look like
    $df = $cop |> blah
which adds an extra indirection to every use, which seems stupid.  See
#4138 for an example (although the regression reported there
wasn't due to the indirection).

There is an awkward wrinkle though: we want to be very
careful when we have
    instance C a => C [a] where
      {-# INLINE op #-}
      op = ...
then we'll get an INLINE pragma on $cop_list but it's important that
$cop_list only inlines when it's applied to *two* arguments (the
dictionary and the list argument).  So we must not eta-expand $df
above.  We ensure that this doesn't happen by putting an INLINE
pragma on the dfun itself; after all, it ends up being just a cast.

There is one more dark corner to the INLINE story, even more deeply
buried.  Consider this (#3772):

    class DeepSeq a => C a where
      gen :: Int -> a

    instance C a => C [a] where
      gen n = ...

    class DeepSeq a where
      deepSeq :: a -> b -> b

    instance DeepSeq a => DeepSeq [a] where
      {-# INLINE deepSeq #-}
      deepSeq xs b = foldr deepSeq b xs

That gives rise to these defns:

    $cdeepSeq :: DeepSeq a -> [a] -> b -> b
    -- User INLINE( 3 args )!
    $cdeepSeq a (d:DS a) b (x:[a]) (y:b) = ...

    $fDeepSeq[] :: DeepSeq a -> DeepSeq [a]
    -- DFun (with auto INLINE pragma)
    $fDeepSeq[] a d = $cdeepSeq a d |> blah

    $cp1 a d :: C a => DeepSep [a]
    -- We don't want to eta-expand this, lest
    -- $cdeepSeq gets inlined in it!
    $cp1 a d = $fDeepSep[] a (scsel a d)

    $fC[] :: C a => C [a]
    -- Ordinary DFun
    $fC[] a d = MkC ($cp1 a d) ($cgen a d)

Here $cp1 is the code that generates the superclass for C [a].  The
issue is this: we must not eta-expand $cp1 either, or else $fDeepSeq[]
and then $cdeepSeq will inline there, which is definitely wrong.  Like
on the dfun, we solve this by adding an INLINE pragma to $cp1.

Note [Subtle interaction of recursion and overlap]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this
  class C a where { op1,op2 :: a -> a }
  instance C a => C [a] where
    op1 x = op2 x ++ op2 x
    op2 x = ...
  instance C [Int] where
    ...

When type-checking the C [a] instance, we need a C [a] dictionary (for
the call of op2).  If we look up in the instance environment, we find
an overlap.  And in *general* the right thing is to complain (see Note
[Overlapping instances] in GHC.Core.InstEnv).  But in *this* case it's wrong to
complain, because we just want to delegate to the op2 of this same
instance.

Why is this justified?  Because we generate a (C [a]) constraint in
a context in which 'a' cannot be instantiated to anything that matches
other overlapping instances, or else we would not be executing this
version of op1 in the first place.

It might even be a bit disguised:

  nullFail :: C [a] => [a] -> [a]
  nullFail x = op2 x ++ op2 x

  instance C a => C [a] where
    op1 x = nullFail x

Precisely this is used in package 'regex-base', module Context.hs.
See the overlapping instances for RegexContext, and the fact that they
call 'nullFail' just like the example above.  The DoCon package also
does the same thing; it shows up in module Fraction.hs.

Conclusion: when typechecking the methods in a C [a] instance, we want to
treat the 'a' as an *existential* type variable, in the sense described
by Note [Binding when looking up instances].  That is why isOverlappableTyVar
responds True to an InstSkol, which is the kind of skolem we use in
tcInstDecl2.


Note [Tricky type variable scoping]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In our example
        class C a where
           op1, op2 :: Ix b => a -> b -> b
           op2 = <dm-rhs>

        instance C a => C [a]
           {-# INLINE [2] op1 #-}
           op1 = <rhs>

note that 'a' and 'b' are *both* in scope in <dm-rhs>, but only 'a' is
in scope in <rhs>.  In particular, we must make sure that 'b' is in
scope when typechecking <dm-rhs>.  This is achieved by subFunTys,
which brings appropriate tyvars into scope. This happens for both
<dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
complained if 'b' is mentioned in <rhs>.



************************************************************************
*                                                                      *
\subsection{Extracting instance decls}
*                                                                      *
************************************************************************

Gather up the instance declarations from their various sources
-}

tcInstDecls1    -- Deal with both source-code and imported instance decls
   :: [LInstDecl GhcRn]         -- Source code instance decls
   -> TcM (TcGblEnv,            -- The full inst env
           [InstInfo GhcRn],    -- Source-code instance decls to process;
                                -- contains all dfuns for this module
           [DerivInfo])         -- From data family instances

tcInstDecls1 :: [LInstDecl (GhcPass 'Renamed)]
-> TcM (TcGblEnv, [InstInfo (GhcPass 'Renamed)], [DerivInfo])
tcInstDecls1 [LInstDecl (GhcPass 'Renamed)]
inst_decls
  = do {    -- Do class and family instance declarations
       ; [([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])]
stuff <- forall a b. (a -> TcRn b) -> [a] -> TcRn [b]
mapAndRecoverM LInstDecl (GhcPass 'Renamed)
-> TcM ([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])
tcLocalInstDecl [LInstDecl (GhcPass 'Renamed)]
inst_decls

       ; let ([[InstInfo (GhcPass 'Renamed)]]
local_infos_s, [[FamInst]]
fam_insts_s, [[DerivInfo]]
datafam_deriv_infos) = forall a b c. [(a, b, c)] -> ([a], [b], [c])
unzip3 [([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])]
stuff
             fam_insts :: [FamInst]
fam_insts   = forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[FamInst]]
fam_insts_s
             local_infos :: [InstInfo (GhcPass 'Renamed)]
local_infos = forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[InstInfo (GhcPass 'Renamed)]]
local_infos_s

       ; TcGblEnv
gbl_env <- forall a. [InstInfo (GhcPass 'Renamed)] -> TcM a -> TcM a
addClsInsts [InstInfo (GhcPass 'Renamed)]
local_infos forall a b. (a -> b) -> a -> b
$
                    forall a. [FamInst] -> TcM a -> TcM a
addFamInsts [FamInst]
fam_insts   forall a b. (a -> b) -> a -> b
$
                    forall gbl lcl. TcRnIf gbl lcl gbl
getGblEnv

       ; forall (m :: * -> *) a. Monad m => a -> m a
return ( TcGblEnv
gbl_env
                , [InstInfo (GhcPass 'Renamed)]
local_infos
                , forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[DerivInfo]]
datafam_deriv_infos ) }

-- | Use DerivInfo for data family instances (produced by tcInstDecls1),
--   datatype declarations (TyClDecl), and standalone deriving declarations
--   (DerivDecl) to check and process all derived class instances.
tcInstDeclsDeriv
  :: [DerivInfo]
  -> [LDerivDecl GhcRn]
  -> TcM (TcGblEnv, [InstInfo GhcRn], HsValBinds GhcRn)
tcInstDeclsDeriv :: [DerivInfo]
-> [LDerivDecl (GhcPass 'Renamed)]
-> TcM
     (TcGblEnv, [InstInfo (GhcPass 'Renamed)],
      HsValBinds (GhcPass 'Renamed))
tcInstDeclsDeriv [DerivInfo]
deriv_infos [LDerivDecl (GhcPass 'Renamed)]
derivds
  = do ThStage
th_stage <- TcM ThStage
getStage -- See Note [Deriving inside TH brackets]
       if ThStage -> Bool
isBrackStage ThStage
th_stage
       then do { TcGblEnv
gbl_env <- forall gbl lcl. TcRnIf gbl lcl gbl
getGblEnv
               ; forall (m :: * -> *) a. Monad m => a -> m a
return (TcGblEnv
gbl_env, forall a. Bag a -> [a]
bagToList forall a. Bag a
emptyBag, forall (a :: Pass) (b :: Pass).
HsValBindsLR (GhcPass a) (GhcPass b)
emptyValBindsOut) }
       else do { (TcGblEnv
tcg_env, Bag (InstInfo (GhcPass 'Renamed))
info_bag, HsValBinds (GhcPass 'Renamed)
valbinds) <- [DerivInfo]
-> [LDerivDecl (GhcPass 'Renamed)]
-> TcM
     (TcGblEnv, Bag (InstInfo (GhcPass 'Renamed)),
      HsValBinds (GhcPass 'Renamed))
tcDeriving [DerivInfo]
deriv_infos [LDerivDecl (GhcPass 'Renamed)]
derivds
               ; forall (m :: * -> *) a. Monad m => a -> m a
return (TcGblEnv
tcg_env, forall a. Bag a -> [a]
bagToList Bag (InstInfo (GhcPass 'Renamed))
info_bag, HsValBinds (GhcPass 'Renamed)
valbinds) }

addClsInsts :: [InstInfo GhcRn] -> TcM a -> TcM a
addClsInsts :: forall a. [InstInfo (GhcPass 'Renamed)] -> TcM a -> TcM a
addClsInsts [InstInfo (GhcPass 'Renamed)]
infos TcM a
thing_inside
  = forall a. [ClsInst] -> TcM a -> TcM a
tcExtendLocalInstEnv (forall a b. (a -> b) -> [a] -> [b]
map forall a. InstInfo a -> ClsInst
iSpec [InstInfo (GhcPass 'Renamed)]
infos) TcM a
thing_inside

addFamInsts :: [FamInst] -> TcM a -> TcM a
-- Extend (a) the family instance envt
--        (b) the type envt with stuff from data type decls
addFamInsts :: forall a. [FamInst] -> TcM a -> TcM a
addFamInsts [FamInst]
fam_insts TcM a
thing_inside
  = forall a. [FamInst] -> TcM a -> TcM a
tcExtendLocalFamInstEnv [FamInst]
fam_insts forall a b. (a -> b) -> a -> b
$
    forall r. [TyThing] -> TcM r -> TcM r
tcExtendGlobalEnv [TyThing]
axioms          forall a b. (a -> b) -> a -> b
$
    do { String -> SDoc -> TcRn ()
traceTc String
"addFamInsts" ([FamInst] -> SDoc
pprFamInsts [FamInst]
fam_insts)
       ; TcGblEnv
gbl_env <- [TyCon] -> TcM TcGblEnv
addTyConsToGblEnv [TyCon]
data_rep_tycons
                    -- Does not add its axiom; that comes
                    -- from adding the 'axioms' above
       ; forall gbl lcl a. gbl -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
setGblEnv TcGblEnv
gbl_env TcM a
thing_inside }
  where
    axioms :: [TyThing]
axioms = forall a b. (a -> b) -> [a] -> [b]
map (CoAxiom Branched -> TyThing
ACoAxiom forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (br :: BranchFlag). CoAxiom br -> CoAxiom Branched
toBranchedAxiom forall b c a. (b -> c) -> (a -> b) -> a -> c
. FamInst -> CoAxiom Unbranched
famInstAxiom) [FamInst]
fam_insts
    data_rep_tycons :: [TyCon]
data_rep_tycons = [FamInst] -> [TyCon]
famInstsRepTyCons [FamInst]
fam_insts
      -- The representation tycons for 'data instances' declarations

{-
Note [Deriving inside TH brackets]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Given a declaration bracket
  [d| data T = A | B deriving( Show ) |]

there is really no point in generating the derived code for deriving(
Show) and then type-checking it. This will happen at the call site
anyway, and the type check should never fail!  Moreover (#6005)
the scoping of the generated code inside the bracket does not seem to
work out.

The easy solution is simply not to generate the derived instances at
all.  (A less brutal solution would be to generate them with no
bindings.)  This will become moot when we shift to the new TH plan, so
the brutal solution will do.
-}

tcLocalInstDecl :: LInstDecl GhcRn
                -> TcM ([InstInfo GhcRn], [FamInst], [DerivInfo])
        -- A source-file instance declaration
        -- Type-check all the stuff before the "where"
        --
        -- We check for respectable instance type, and context
tcLocalInstDecl :: LInstDecl (GhcPass 'Renamed)
-> TcM ([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])
tcLocalInstDecl (L SrcSpanAnnA
loc (TyFamInstD { tfid_inst :: forall pass. InstDecl pass -> TyFamInstDecl pass
tfid_inst = TyFamInstDecl (GhcPass 'Renamed)
decl }))
  = do { FamInst
fam_inst <- AssocInstInfo -> LTyFamInstDecl (GhcPass 'Renamed) -> TcM FamInst
tcTyFamInstDecl AssocInstInfo
NotAssociated (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc TyFamInstDecl (GhcPass 'Renamed)
decl)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([], [FamInst
fam_inst], []) }

tcLocalInstDecl (L SrcSpanAnnA
loc (DataFamInstD { dfid_inst :: forall pass. InstDecl pass -> DataFamInstDecl pass
dfid_inst = DataFamInstDecl (GhcPass 'Renamed)
decl }))
  = do { (FamInst
fam_inst, Maybe DerivInfo
m_deriv_info) <- AssocInstInfo
-> TyVarEnv Name
-> LDataFamInstDecl (GhcPass 'Renamed)
-> TcM (FamInst, Maybe DerivInfo)
tcDataFamInstDecl AssocInstInfo
NotAssociated forall a. VarEnv a
emptyVarEnv (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc DataFamInstDecl (GhcPass 'Renamed)
decl)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([], [FamInst
fam_inst], forall a. Maybe a -> [a]
maybeToList Maybe DerivInfo
m_deriv_info) }

tcLocalInstDecl (L SrcSpanAnnA
loc (ClsInstD { cid_inst :: forall pass. InstDecl pass -> ClsInstDecl pass
cid_inst = ClsInstDecl (GhcPass 'Renamed)
decl }))
  = do { ([InstInfo (GhcPass 'Renamed)]
insts, [FamInst]
fam_insts, [DerivInfo]
deriv_infos) <- LClsInstDecl (GhcPass 'Renamed)
-> TcM ([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])
tcClsInstDecl (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc ClsInstDecl (GhcPass 'Renamed)
decl)
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([InstInfo (GhcPass 'Renamed)]
insts, [FamInst]
fam_insts, [DerivInfo]
deriv_infos) }

tcClsInstDecl :: LClsInstDecl GhcRn
              -> TcM ([InstInfo GhcRn], [FamInst], [DerivInfo])
-- The returned DerivInfos are for any associated data families
tcClsInstDecl :: LClsInstDecl (GhcPass 'Renamed)
-> TcM ([InstInfo (GhcPass 'Renamed)], [FamInst], [DerivInfo])
tcClsInstDecl (L SrcSpanAnnA
loc (ClsInstDecl { cid_poly_ty :: forall pass. ClsInstDecl pass -> LHsSigType pass
cid_poly_ty = LHsSigType (GhcPass 'Renamed)
hs_ty, cid_binds :: forall pass. ClsInstDecl pass -> LHsBinds pass
cid_binds = LHsBinds (GhcPass 'Renamed)
binds
                                  , cid_sigs :: forall pass. ClsInstDecl pass -> [LSig pass]
cid_sigs = [LSig (GhcPass 'Renamed)]
uprags, cid_tyfam_insts :: forall pass. ClsInstDecl pass -> [LTyFamInstDecl pass]
cid_tyfam_insts = [LTyFamInstDecl (GhcPass 'Renamed)]
ats
                                  , cid_overlap_mode :: forall pass. ClsInstDecl pass -> Maybe (XRec pass OverlapMode)
cid_overlap_mode = Maybe (XRec (GhcPass 'Renamed) OverlapMode)
overlap_mode
                                  , cid_datafam_insts :: forall pass. ClsInstDecl pass -> [LDataFamInstDecl pass]
cid_datafam_insts = [LDataFamInstDecl (GhcPass 'Renamed)]
adts }))
  = forall ann a. SrcSpanAnn' ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc                      forall a b. (a -> b) -> a -> b
$
    forall a. SDoc -> TcM a -> TcM a
addErrCtxt (LHsSigType (GhcPass 'Renamed) -> SDoc
instDeclCtxt1 LHsSigType (GhcPass 'Renamed)
hs_ty)  forall a b. (a -> b) -> a -> b
$
    do  { PredType
dfun_ty <- UserTypeCtxt -> LHsSigType (GhcPass 'Renamed) -> TcM PredType
tcHsClsInstType (Bool -> UserTypeCtxt
InstDeclCtxt Bool
False) LHsSigType (GhcPass 'Renamed)
hs_ty
        ; let ([Id]
tyvars, [PredType]
theta, Class
clas, [PredType]
inst_tys) = PredType -> ([Id], [PredType], Class, [PredType])
tcSplitDFunTy PredType
dfun_ty
             -- NB: tcHsClsInstType does checkValidInstance

        ; (TCvSubst
subst, [Id]
skol_tvs) <- [Id] -> TcM (TCvSubst, [Id])
tcInstSkolTyVars [Id]
tyvars
        ; let tv_skol_prs :: [(Name, Id)]
tv_skol_prs = [ (Id -> Name
tyVarName Id
tv, Id
skol_tv)
                            | (Id
tv, Id
skol_tv) <- [Id]
tyvars forall a b. [a] -> [b] -> [(a, b)]
`zip` [Id]
skol_tvs ]
              -- Map from the skolemized Names to the original Names.
              -- See Note [Associated data family instances and di_scoped_tvs].
              tv_skol_env :: TyVarEnv Name
tv_skol_env = forall a. [(Id, a)] -> VarEnv a
mkVarEnv forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map forall a b. (a, b) -> (b, a)
swap [(Name, Id)]
tv_skol_prs
              n_inferred :: Int
n_inferred = forall a. (a -> Bool) -> [a] -> Int
countWhile ((forall a. Eq a => a -> a -> Bool
== ArgFlag
Inferred) forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall tv argf. VarBndr tv argf -> argf
binderArgFlag) forall a b. (a -> b) -> a -> b
$
                           forall a b. (a, b) -> a
fst forall a b. (a -> b) -> a -> b
$ PredType -> ([VarBndr Id ArgFlag], PredType)
splitForAllTyCoVarBinders PredType
dfun_ty
              visible_skol_tvs :: [Id]
visible_skol_tvs = forall a. Int -> [a] -> [a]
drop Int
n_inferred [Id]
skol_tvs

        ; String -> SDoc -> TcRn ()
traceTc String
"tcLocalInstDecl 1" (forall a. Outputable a => a -> SDoc
ppr PredType
dfun_ty SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr (PredType -> Int
invisibleTyBndrCount PredType
dfun_ty) SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr [Id]
skol_tvs)

        -- Next, process any associated types.
        ; ([(FamInst, Maybe DerivInfo)]
datafam_stuff, [FamInst]
tyfam_insts)
             <- forall r. [(Name, Id)] -> TcM r -> TcM r
tcExtendNameTyVarEnv [(Name, Id)]
tv_skol_prs forall a b. (a -> b) -> a -> b
$
                do  { let mini_env :: VarEnv PredType
mini_env   = forall a. [(Id, a)] -> VarEnv a
mkVarEnv (Class -> [Id]
classTyVars Class
clas forall a b. [a] -> [b] -> [(a, b)]
`zip` HasCallStack => TCvSubst -> [PredType] -> [PredType]
substTys TCvSubst
subst [PredType]
inst_tys)
                          mini_subst :: TCvSubst
mini_subst = InScopeSet -> VarEnv PredType -> TCvSubst
mkTvSubst (VarSet -> InScopeSet
mkInScopeSet ([Id] -> VarSet
mkVarSet [Id]
skol_tvs)) VarEnv PredType
mini_env
                          mb_info :: AssocInstInfo
mb_info    = InClsInst { ai_class :: Class
ai_class = Class
clas
                                                 , ai_tyvars :: [Id]
ai_tyvars = [Id]
visible_skol_tvs
                                                 , ai_inst_env :: VarEnv PredType
ai_inst_env = VarEnv PredType
mini_env }
                    ; [(FamInst, Maybe DerivInfo)]
df_stuff  <- forall a b. (a -> TcRn b) -> [a] -> TcRn [b]
mapAndRecoverM (AssocInstInfo
-> TyVarEnv Name
-> LDataFamInstDecl (GhcPass 'Renamed)
-> TcM (FamInst, Maybe DerivInfo)
tcDataFamInstDecl AssocInstInfo
mb_info TyVarEnv Name
tv_skol_env) [LDataFamInstDecl (GhcPass 'Renamed)]
adts
                    ; [FamInst]
tf_insts1 <- forall a b. (a -> TcRn b) -> [a] -> TcRn [b]
mapAndRecoverM (AssocInstInfo -> LTyFamInstDecl (GhcPass 'Renamed) -> TcM FamInst
tcTyFamInstDecl AssocInstInfo
mb_info)   [LTyFamInstDecl (GhcPass 'Renamed)]
ats

                      -- Check for missing associated types and build them
                      -- from their defaults (if available)
                    ; Bool
is_boot <- TcRn Bool
tcIsHsBootOrSig
                    ; let atItems :: [ClassATItem]
atItems = Class -> [ClassATItem]
classATItems Class
clas
                    ; [[FamInst]]
tf_insts2 <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (SrcSpan -> TCvSubst -> NameSet -> ClassATItem -> TcM [FamInst]
tcATDefault (forall a. SrcSpanAnn' a -> SrcSpan
locA SrcSpanAnnA
loc) TCvSubst
mini_subst NameSet
defined_ats)
                                        (if Bool
is_boot then [] else [ClassATItem]
atItems)
                      -- Don't default type family instances, but rather omit, in hsig/hs-boot.
                      -- Since hsig/hs-boot files are essentially large binders we want omission
                      -- of the definition to result in no restriction, rather than for example
                      -- attempting to "pattern match" with the invisible defaults and generate
                      -- equalities. Without further handling, this would just result in a panic
                      -- anyway.
                      -- See https://github.com/ghc-proposals/ghc-proposals/pull/320 for
                      -- additional discussion.
                    ; forall (m :: * -> *) a. Monad m => a -> m a
return ([(FamInst, Maybe DerivInfo)]
df_stuff, [FamInst]
tf_insts1 forall a. [a] -> [a] -> [a]
++ forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[FamInst]]
tf_insts2) }


        -- Finally, construct the Core representation of the instance.
        -- (This no longer includes the associated types.)
        ; Name
dfun_name <- Class -> [PredType] -> SrcSpan -> TcM Name
newDFunName Class
clas [PredType]
inst_tys (forall a e. GenLocated (SrcSpanAnn' a) e -> SrcSpan
getLocA LHsSigType (GhcPass 'Renamed)
hs_ty)
                -- Dfun location is that of instance *header*

        ; ClsInst
ispec <- Maybe OverlapMode
-> Name -> [Id] -> [PredType] -> Class -> [PredType] -> TcM ClsInst
newClsInst (forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall l e. GenLocated l e -> e
unLoc Maybe (XRec (GhcPass 'Renamed) OverlapMode)
overlap_mode) Name
dfun_name
                              [Id]
tyvars [PredType]
theta Class
clas [PredType]
inst_tys

        ; let inst_binds :: InstBindings (GhcPass 'Renamed)
inst_binds = InstBindings
                             { ib_binds :: LHsBinds (GhcPass 'Renamed)
ib_binds = LHsBinds (GhcPass 'Renamed)
binds
                             , ib_tyvars :: [Name]
ib_tyvars = forall a b. (a -> b) -> [a] -> [b]
map Id -> Name
Var.varName [Id]
tyvars -- Scope over bindings
                             , ib_pragmas :: [LSig (GhcPass 'Renamed)]
ib_pragmas = [LSig (GhcPass 'Renamed)]
uprags
                             , ib_extensions :: [Extension]
ib_extensions = []
                             , ib_derived :: Bool
ib_derived = Bool
False }
              inst_info :: InstInfo (GhcPass 'Renamed)
inst_info = InstInfo { iSpec :: ClsInst
iSpec  = ClsInst
ispec, iBinds :: InstBindings (GhcPass 'Renamed)
iBinds = InstBindings (GhcPass 'Renamed)
inst_binds }

              ([FamInst]
datafam_insts, [Maybe DerivInfo]
m_deriv_infos) = forall a b. [(a, b)] -> ([a], [b])
unzip [(FamInst, Maybe DerivInfo)]
datafam_stuff
              deriv_infos :: [DerivInfo]
deriv_infos                    = forall a. [Maybe a] -> [a]
catMaybes [Maybe DerivInfo]
m_deriv_infos
              all_insts :: [FamInst]
all_insts                      = [FamInst]
tyfam_insts forall a. [a] -> [a] -> [a]
++ [FamInst]
datafam_insts

         -- In hs-boot files there should be no bindings
        ; let no_binds :: Bool
no_binds = forall (idL :: Pass) idR. LHsBindsLR (GhcPass idL) idR -> Bool
isEmptyLHsBinds LHsBinds (GhcPass 'Renamed)
binds Bool -> Bool -> Bool
&& forall (t :: * -> *) a. Foldable t => t a -> Bool
null [LSig (GhcPass 'Renamed)]
uprags
        ; Bool
is_boot <- TcRn Bool
tcIsHsBootOrSig
        ; Bool -> SDoc -> TcRn ()
failIfTc (Bool
is_boot Bool -> Bool -> Bool
&& Bool -> Bool
not Bool
no_binds) SDoc
badBootDeclErr

        ; forall (m :: * -> *) a. Monad m => a -> m a
return ( [InstInfo (GhcPass 'Renamed)
inst_info], [FamInst]
all_insts, [DerivInfo]
deriv_infos ) }
  where
    defined_ats :: NameSet
defined_ats = [Name] -> NameSet
mkNameSet (forall a b. (a -> b) -> [a] -> [b]
map (forall (p :: Pass).
(Anno (IdGhcP p) ~ SrcSpanAnnN) =>
TyFamInstDecl (GhcPass p) -> IdP (GhcPass p)
tyFamInstDeclName forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall l e. GenLocated l e -> e
unLoc) [LTyFamInstDecl (GhcPass 'Renamed)]
ats)
                  NameSet -> NameSet -> NameSet
`unionNameSet`
                  [Name] -> NameSet
mkNameSet (forall a b. (a -> b) -> [a] -> [b]
map (forall l e. GenLocated l e -> e
unLoc forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon
                                        forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall pass. DataFamInstDecl pass -> FamEqn pass (HsDataDefn pass)
dfid_eqn
                                        forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall l e. GenLocated l e -> e
unLoc) [LDataFamInstDecl (GhcPass 'Renamed)]
adts)

{-
************************************************************************
*                                                                      *
               Type family instances
*                                                                      *
************************************************************************

Family instances are somewhat of a hybrid.  They are processed together with
class instance heads, but can contain data constructors and hence they share a
lot of kinding and type checking code with ordinary algebraic data types (and
GADTs).
-}

tcTyFamInstDecl :: AssocInstInfo
                -> LTyFamInstDecl GhcRn -> TcM FamInst
  -- "type instance"
  -- See Note [Associated type instances]
tcTyFamInstDecl :: AssocInstInfo -> LTyFamInstDecl (GhcPass 'Renamed) -> TcM FamInst
tcTyFamInstDecl AssocInstInfo
mb_clsinfo (L SrcSpanAnnA
loc decl :: TyFamInstDecl (GhcPass 'Renamed)
decl@(TyFamInstDecl { tfid_eqn :: forall pass. TyFamInstDecl pass -> TyFamInstEqn pass
tfid_eqn = TyFamInstEqn (GhcPass 'Renamed)
eqn }))
  = forall ann a. SrcSpanAnn' ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc           forall a b. (a -> b) -> a -> b
$
    forall a. TyFamInstDecl (GhcPass 'Renamed) -> TcM a -> TcM a
tcAddTyFamInstCtxt TyFamInstDecl (GhcPass 'Renamed)
decl  forall a b. (a -> b) -> a -> b
$
    do { let fam_lname :: LIdP (GhcPass 'Renamed)
fam_lname = forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon TyFamInstEqn (GhcPass 'Renamed)
eqn
       ; TyCon
fam_tc <- GenLocated SrcSpanAnnN Name -> TcM TyCon
tcLookupLocatedTyCon LIdP (GhcPass 'Renamed)
fam_lname
       ; AssocInstInfo -> TyCon -> TcRn ()
tcFamInstDeclChecks AssocInstInfo
mb_clsinfo TyCon
fam_tc

         -- (0) Check it's an open type family
       ; Bool -> SDoc -> TcRn ()
checkTc (TyCon -> Bool
isTypeFamilyTyCon TyCon
fam_tc)     (TyCon -> SDoc
wrongKindOfFamily TyCon
fam_tc)
       ; Bool -> SDoc -> TcRn ()
checkTc (TyCon -> Bool
isOpenTypeFamilyTyCon TyCon
fam_tc) (TyCon -> SDoc
notOpenFamily TyCon
fam_tc)

         -- (1) do the work of verifying the synonym group
         -- For some reason we don't have a location for the equation
         -- itself, so we make do with the location of family name
       ; KnotTied CoAxBranch
co_ax_branch <- TyCon
-> AssocInstInfo
-> LTyFamInstEqn (GhcPass 'Renamed)
-> TcM (KnotTied CoAxBranch)
tcTyFamInstEqn TyCon
fam_tc AssocInstInfo
mb_clsinfo
                                        (forall l e. l -> e -> GenLocated l e
L (forall a ann. SrcSpanAnn' a -> SrcAnn ann
na2la forall a b. (a -> b) -> a -> b
$ forall l e. GenLocated l e -> l
getLoc LIdP (GhcPass 'Renamed)
fam_lname) TyFamInstEqn (GhcPass 'Renamed)
eqn)

         -- (2) check for validity
       ; AssocInstInfo -> TyCon -> KnotTied CoAxBranch -> TcRn ()
checkConsistentFamInst AssocInstInfo
mb_clsinfo TyCon
fam_tc KnotTied CoAxBranch
co_ax_branch
       ; TyCon -> KnotTied CoAxBranch -> TcRn ()
checkValidCoAxBranch TyCon
fam_tc KnotTied CoAxBranch
co_ax_branch

         -- (3) construct coercion axiom
       ; Name
rep_tc_name <- GenLocated SrcSpanAnnN Name -> [[PredType]] -> TcM Name
newFamInstAxiomName LIdP (GhcPass 'Renamed)
fam_lname [KnotTied CoAxBranch -> [PredType]
coAxBranchLHS KnotTied CoAxBranch
co_ax_branch]
       ; let axiom :: CoAxiom Unbranched
axiom = Name -> TyCon -> KnotTied CoAxBranch -> CoAxiom Unbranched
mkUnbranchedCoAxiom Name
rep_tc_name TyCon
fam_tc KnotTied CoAxBranch
co_ax_branch
       ; FamFlavor -> CoAxiom Unbranched -> TcM FamInst
newFamInst FamFlavor
SynFamilyInst CoAxiom Unbranched
axiom }


---------------------
tcFamInstDeclChecks :: AssocInstInfo -> TyCon -> TcM ()
-- Used for both type and data families
tcFamInstDeclChecks :: AssocInstInfo -> TyCon -> TcRn ()
tcFamInstDeclChecks AssocInstInfo
mb_clsinfo TyCon
fam_tc
  = do { -- Type family instances require -XTypeFamilies
         -- and can't (currently) be in an hs-boot file
       ; String -> SDoc -> TcRn ()
traceTc String
"tcFamInstDecl" (forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc)
       ; Bool
type_families <- forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.TypeFamilies
       ; Bool
is_boot       <- TcRn Bool
tcIsHsBootOrSig   -- Are we compiling an hs-boot file?
       ; Bool -> SDoc -> TcRn ()
checkTc Bool
type_families forall a b. (a -> b) -> a -> b
$ TyCon -> SDoc
badFamInstDecl TyCon
fam_tc
       ; Bool -> SDoc -> TcRn ()
checkTc (Bool -> Bool
not Bool
is_boot) forall a b. (a -> b) -> a -> b
$ SDoc
badBootFamInstDeclErr

       -- Check that it is a family TyCon, and that
       -- oplevel type instances are not for associated types.
       ; Bool -> SDoc -> TcRn ()
checkTc (TyCon -> Bool
isFamilyTyCon TyCon
fam_tc) (TyCon -> SDoc
notFamily TyCon
fam_tc)

       ; forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (AssocInstInfo -> Bool
isNotAssociated AssocInstInfo
mb_clsinfo Bool -> Bool -> Bool
&&   -- Not in a class decl
               TyCon -> Bool
isTyConAssoc TyCon
fam_tc)            -- but an associated type
              (SDoc -> TcRn ()
addErr forall a b. (a -> b) -> a -> b
$ TyCon -> SDoc
assocInClassErr TyCon
fam_tc)
       }

{- Note [Associated type instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We allow this:
  class C a where
    type T x a
  instance C Int where
    type T (S y) Int = y
    type T Z     Int = Char

Note that
  a) The variable 'x' is not bound by the class decl
  b) 'x' is instantiated to a non-type-variable in the instance
  c) There are several type instance decls for T in the instance

All this is fine.  Of course, you can't give any *more* instances
for (T ty Int) elsewhere, because it's an *associated* type.


************************************************************************
*                                                                      *
               Data family instances
*                                                                      *
************************************************************************

For some reason data family instances are a lot more complicated
than type family instances
-}

tcDataFamInstDecl ::
     AssocInstInfo
  -> TyVarEnv Name -- If this is an associated data family instance, maps the
                   -- parent class's skolemized type variables to their
                   -- original Names. If this is a non-associated instance,
                   -- this will be empty.
                   -- See Note [Associated data family instances and di_scoped_tvs].
  -> LDataFamInstDecl GhcRn -> TcM (FamInst, Maybe DerivInfo)
  -- "newtype instance" and "data instance"
tcDataFamInstDecl :: AssocInstInfo
-> TyVarEnv Name
-> LDataFamInstDecl (GhcPass 'Renamed)
-> TcM (FamInst, Maybe DerivInfo)
tcDataFamInstDecl AssocInstInfo
mb_clsinfo TyVarEnv Name
tv_skol_env
    (L SrcSpanAnnA
loc decl :: DataFamInstDecl (GhcPass 'Renamed)
decl@(DataFamInstDecl { dfid_eqn :: forall pass. DataFamInstDecl pass -> FamEqn pass (HsDataDefn pass)
dfid_eqn =
      FamEqn { feqn_bndrs :: forall pass rhs. FamEqn pass rhs -> HsOuterFamEqnTyVarBndrs pass
feqn_bndrs  = HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
outer_bndrs
             , feqn_pats :: forall pass rhs. FamEqn pass rhs -> HsTyPats pass
feqn_pats   = HsTyPats (GhcPass 'Renamed)
hs_pats
             , feqn_tycon :: forall pass rhs. FamEqn pass rhs -> LIdP pass
feqn_tycon  = lfam_name :: LIdP (GhcPass 'Renamed)
lfam_name@(L SrcSpanAnnN
_ Name
fam_name)
             , feqn_fixity :: forall pass rhs. FamEqn pass rhs -> LexicalFixity
feqn_fixity = LexicalFixity
fixity
             , feqn_rhs :: forall pass rhs. FamEqn pass rhs -> rhs
feqn_rhs    = HsDataDefn { dd_ND :: forall pass. HsDataDefn pass -> NewOrData
dd_ND      = NewOrData
new_or_data
                                        , dd_cType :: forall pass. HsDataDefn pass -> Maybe (XRec pass CType)
dd_cType   = Maybe (XRec (GhcPass 'Renamed) CType)
cType
                                        , dd_ctxt :: forall pass. HsDataDefn pass -> Maybe (LHsContext pass)
dd_ctxt    = Maybe (LHsContext (GhcPass 'Renamed))
hs_ctxt
                                        , dd_cons :: forall pass. HsDataDefn pass -> [LConDecl pass]
dd_cons    = [LConDecl (GhcPass 'Renamed)]
hs_cons
                                        , dd_kindSig :: forall pass. HsDataDefn pass -> Maybe (LHsKind pass)
dd_kindSig = Maybe (LHsKind (GhcPass 'Renamed))
m_ksig
                                        , dd_derivs :: forall pass. HsDataDefn pass -> HsDeriving pass
dd_derivs  = HsDeriving (GhcPass 'Renamed)
derivs } }}))
  = forall ann a. SrcSpanAnn' ann -> TcRn a -> TcRn a
setSrcSpanA SrcSpanAnnA
loc            forall a b. (a -> b) -> a -> b
$
    forall a. DataFamInstDecl (GhcPass 'Renamed) -> TcM a -> TcM a
tcAddDataFamInstCtxt DataFamInstDecl (GhcPass 'Renamed)
decl  forall a b. (a -> b) -> a -> b
$
    do { TyCon
fam_tc <- GenLocated SrcSpanAnnN Name -> TcM TyCon
tcLookupLocatedTyCon LIdP (GhcPass 'Renamed)
lfam_name

       ; AssocInstInfo -> TyCon -> TcRn ()
tcFamInstDeclChecks AssocInstInfo
mb_clsinfo TyCon
fam_tc

       -- Check that the family declaration is for the right kind
       ; Bool -> SDoc -> TcRn ()
checkTc (TyCon -> Bool
isDataFamilyTyCon TyCon
fam_tc) (TyCon -> SDoc
wrongKindOfFamily TyCon
fam_tc)
       ; Bool
gadt_syntax <- Name
-> NewOrData
-> Maybe (LHsContext (GhcPass 'Renamed))
-> [LConDecl (GhcPass 'Renamed)]
-> TcRn Bool
dataDeclChecks Name
fam_name NewOrData
new_or_data Maybe (LHsContext (GhcPass 'Renamed))
hs_ctxt [LConDecl (GhcPass 'Renamed)]
hs_cons
          -- Do /not/ check that the number of patterns = tyConArity fam_tc
          -- See [Arity of data families] in GHC.Core.FamInstEnv
       ; ([Id]
qtvs, [PredType]
pats, PredType
res_kind, [PredType]
stupid_theta)
             <- AssocInstInfo
-> TyCon
-> HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
-> LexicalFixity
-> Maybe (LHsContext (GhcPass 'Renamed))
-> HsTyPats (GhcPass 'Renamed)
-> Maybe (LHsKind (GhcPass 'Renamed))
-> NewOrData
-> TcM ([Id], [PredType], PredType, [PredType])
tcDataFamInstHeader AssocInstInfo
mb_clsinfo TyCon
fam_tc HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
outer_bndrs LexicalFixity
fixity
                                    Maybe (LHsContext (GhcPass 'Renamed))
hs_ctxt HsTyPats (GhcPass 'Renamed)
hs_pats Maybe (LHsKind (GhcPass 'Renamed))
m_ksig NewOrData
new_or_data

       -- Eta-reduce the axiom if possible
       -- Quite tricky: see Note [Implementing eta reduction for data families]
       ; let ([PredType]
eta_pats, [TyConBinder]
eta_tcbs) = TyCon -> [PredType] -> ([PredType], [TyConBinder])
eta_reduce TyCon
fam_tc [PredType]
pats
             eta_tvs :: [Id]
eta_tvs       = forall a b. (a -> b) -> [a] -> [b]
map forall tv argf. VarBndr tv argf -> tv
binderVar [TyConBinder]
eta_tcbs
             post_eta_qtvs :: [Id]
post_eta_qtvs = forall a. (a -> Bool) -> [a] -> [a]
filterOut (forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Id]
eta_tvs) [Id]
qtvs

             full_tcbs :: [TyConBinder]
full_tcbs = [Id] -> VarSet -> [TyConBinder]
mkTyConBindersPreferAnon [Id]
post_eta_qtvs
                            (PredType -> VarSet
tyCoVarsOfType ([Id] -> PredType -> PredType
mkSpecForAllTys [Id]
eta_tvs PredType
res_kind))
                         forall a. [a] -> [a] -> [a]
++ [TyConBinder]
eta_tcbs
                 -- Put the eta-removed tyvars at the end
                 -- Remember, qtvs is in arbitrary order, except kind vars are
                 -- first, so there is no reason to suppose that the eta_tvs
                 -- (obtained from the pats) are at the end (#11148)

       -- Eta-expand the representation tycon until it has result
       -- kind `TYPE r`, for some `r`. If UnliftedNewtypes is not enabled, we
       -- go one step further and ensure that it has kind `TYPE 'LiftedRep`.
       --
       -- See also Note [Arity of data families] in GHC.Core.FamInstEnv
       -- NB: we can do this after eta-reducing the axiom, because if
       --     we did it before the "extra" tvs from etaExpandAlgTyCon
       --     would always be eta-reduced
       --
       ; ([TyConBinder]
extra_tcbs, PredType
final_res_kind) <- [TyConBinder] -> PredType -> TcM ([TyConBinder], PredType)
etaExpandAlgTyCon [TyConBinder]
full_tcbs PredType
res_kind

       -- Check the result kind; it may come from a user-written signature.
       -- See Note [Datatype return kinds] in GHC.Tc.TyCl point 4(a)
       ; let extra_pats :: [PredType]
extra_pats  = forall a b. (a -> b) -> [a] -> [b]
map (Id -> PredType
mkTyVarTy forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall tv argf. VarBndr tv argf -> tv
binderVar) [TyConBinder]
extra_tcbs
             all_pats :: [PredType]
all_pats    = [PredType]
pats forall a. [a] -> [a] -> [a]
`chkAppend` [PredType]
extra_pats
             orig_res_ty :: PredType
orig_res_ty = TyCon -> [PredType] -> PredType
mkTyConApp TyCon
fam_tc [PredType]
all_pats
             ty_binders :: [TyConBinder]
ty_binders  = [TyConBinder]
full_tcbs forall a. [a] -> [a] -> [a]
`chkAppend` [TyConBinder]
extra_tcbs

       ; String -> SDoc -> TcRn ()
traceTc String
"tcDataFamInstDecl" forall a b. (a -> b) -> a -> b
$
         [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"Fam tycon:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc
              , String -> SDoc
text String
"Pats:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [PredType]
pats
              , String -> SDoc
text String
"visibilities:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr (TyCon -> [PredType] -> [TyConBndrVis]
tcbVisibilities TyCon
fam_tc [PredType]
pats)
              , String -> SDoc
text String
"all_pats:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [PredType]
all_pats
              , String -> SDoc
text String
"ty_binders" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [TyConBinder]
ty_binders
              , String -> SDoc
text String
"fam_tc_binders:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr (TyCon -> [TyConBinder]
tyConBinders TyCon
fam_tc)
              , String -> SDoc
text String
"res_kind:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr PredType
res_kind
              , String -> SDoc
text String
"final_res_kind:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr PredType
final_res_kind
              , String -> SDoc
text String
"eta_pats" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [PredType]
eta_pats
              , String -> SDoc
text String
"eta_tcbs" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [TyConBinder]
eta_tcbs ]

       ; (TyCon
rep_tc, CoAxiom Unbranched
axiom) <- forall a env. (a -> IOEnv env a) -> IOEnv env a
fixM forall a b. (a -> b) -> a -> b
$ \ ~(TyCon
rec_rep_tc, CoAxiom Unbranched
_) ->
           do { [DataCon]
data_cons <- forall r. [Id] -> TcM r -> TcM r
tcExtendTyVarEnv [Id]
qtvs forall a b. (a -> b) -> a -> b
$
                  -- For H98 decls, the tyvars scope
                  -- over the data constructors
                  NewOrData
-> DataDeclInfo
-> TyCon
-> [TyConBinder]
-> PredType
-> [LConDecl (GhcPass 'Renamed)]
-> TcM [DataCon]
tcConDecls NewOrData
new_or_data (PredType -> DataDeclInfo
DDataInstance PredType
orig_res_ty)
                             TyCon
rec_rep_tc [TyConBinder]
ty_binders PredType
final_res_kind
                             [LConDecl (GhcPass 'Renamed)]
hs_cons

              ; Name
rep_tc_name <- GenLocated SrcSpanAnnN Name -> [PredType] -> TcM Name
newFamInstTyConName LIdP (GhcPass 'Renamed)
lfam_name [PredType]
pats
              ; Name
axiom_name  <- GenLocated SrcSpanAnnN Name -> [[PredType]] -> TcM Name
newFamInstAxiomName LIdP (GhcPass 'Renamed)
lfam_name [[PredType]
pats]
              ; AlgTyConRhs
tc_rhs <- case NewOrData
new_or_data of
                     NewOrData
DataType -> forall (m :: * -> *) a. Monad m => a -> m a
return ([DataCon] -> AlgTyConRhs
mkDataTyConRhs [DataCon]
data_cons)
                     NewOrData
NewType  -> ASSERT( not (null data_cons) )
                                 forall m n. Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
mkNewTyConRhs Name
rep_tc_name TyCon
rec_rep_tc (forall a. [a] -> a
head [DataCon]
data_cons)

              ; let ax_rhs :: PredType
ax_rhs = TyCon -> [PredType] -> PredType
mkTyConApp TyCon
rep_tc ([Id] -> [PredType]
mkTyVarTys [Id]
post_eta_qtvs)
                    axiom :: CoAxiom Unbranched
axiom  = Role
-> Name
-> [Id]
-> [Id]
-> [Id]
-> TyCon
-> [PredType]
-> PredType
-> CoAxiom Unbranched
mkSingleCoAxiom Role
Representational Name
axiom_name
                                 [Id]
post_eta_qtvs [Id]
eta_tvs [] TyCon
fam_tc [PredType]
eta_pats PredType
ax_rhs
                    parent :: AlgTyConFlav
parent = CoAxiom Unbranched -> TyCon -> [PredType] -> AlgTyConFlav
DataFamInstTyCon CoAxiom Unbranched
axiom TyCon
fam_tc [PredType]
all_pats

                      -- NB: Use the full ty_binders from the pats. See bullet toward
                      -- the end of Note [Data type families] in GHC.Core.TyCon
                    rep_tc :: TyCon
rep_tc   = Name
-> [TyConBinder]
-> PredType
-> [Role]
-> Maybe CType
-> [PredType]
-> AlgTyConRhs
-> AlgTyConFlav
-> Bool
-> TyCon
mkAlgTyCon Name
rep_tc_name
                                          [TyConBinder]
ty_binders PredType
final_res_kind
                                          (forall a b. (a -> b) -> [a] -> [b]
map (forall a b. a -> b -> a
const Role
Nominal) [TyConBinder]
ty_binders)
                                          (forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall l e. GenLocated l e -> e
unLoc Maybe (XRec (GhcPass 'Renamed) CType)
cType) [PredType]
stupid_theta
                                          AlgTyConRhs
tc_rhs AlgTyConFlav
parent
                                          Bool
gadt_syntax
                 -- We always assume that indexed types are recursive.  Why?
                 -- (1) Due to their open nature, we can never be sure that a
                 -- further instance might not introduce a new recursive
                 -- dependency.  (2) They are always valid loop breakers as
                 -- they involve a coercion.
              ; forall (m :: * -> *) a. Monad m => a -> m a
return (TyCon
rep_tc, CoAxiom Unbranched
axiom) }

       -- Remember to check validity; no recursion to worry about here
       -- Check that left-hand sides are ok (mono-types, no type families,
       -- consistent instantiations, etc)
       ; let ax_branch :: KnotTied CoAxBranch
ax_branch = CoAxiom Unbranched -> KnotTied CoAxBranch
coAxiomSingleBranch CoAxiom Unbranched
axiom
       ; AssocInstInfo -> TyCon -> KnotTied CoAxBranch -> TcRn ()
checkConsistentFamInst AssocInstInfo
mb_clsinfo TyCon
fam_tc KnotTied CoAxBranch
ax_branch
       ; TyCon -> KnotTied CoAxBranch -> TcRn ()
checkValidCoAxBranch TyCon
fam_tc KnotTied CoAxBranch
ax_branch
       ; TyCon -> TcRn ()
checkValidTyCon TyCon
rep_tc

       ; let scoped_tvs :: [(Name, Id)]
scoped_tvs = forall a b. (a -> b) -> [a] -> [b]
map Id -> (Name, Id)
mk_deriv_info_scoped_tv_pr (TyCon -> [Id]
tyConTyVars TyCon
rep_tc)
             m_deriv_info :: Maybe DerivInfo
m_deriv_info = case HsDeriving (GhcPass 'Renamed)
derivs of
               []    -> forall a. Maybe a
Nothing
               HsDeriving (GhcPass 'Renamed)
preds ->
                 forall a. a -> Maybe a
Just forall a b. (a -> b) -> a -> b
$ DerivInfo { di_rep_tc :: TyCon
di_rep_tc  = TyCon
rep_tc
                                  , di_scoped_tvs :: [(Name, Id)]
di_scoped_tvs = [(Name, Id)]
scoped_tvs
                                  , di_clauses :: HsDeriving (GhcPass 'Renamed)
di_clauses = HsDeriving (GhcPass 'Renamed)
preds
                                  , di_ctxt :: SDoc
di_ctxt    = DataFamInstDecl (GhcPass 'Renamed) -> SDoc
tcMkDataFamInstCtxt DataFamInstDecl (GhcPass 'Renamed)
decl }

       ; FamInst
fam_inst <- FamFlavor -> CoAxiom Unbranched -> TcM FamInst
newFamInst (TyCon -> FamFlavor
DataFamilyInst TyCon
rep_tc) CoAxiom Unbranched
axiom
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (FamInst
fam_inst, Maybe DerivInfo
m_deriv_info) }
  where
    eta_reduce :: TyCon -> [Type] -> ([Type], [TyConBinder])
    -- See Note [Eta reduction for data families] in GHC.Core.Coercion.Axiom
    -- Splits the incoming patterns into two: the [TyVar]
    -- are the patterns that can be eta-reduced away.
    -- e.g.     T [a] Int a d c   ==>  (T [a] Int a, [d,c])
    --
    -- NB: quadratic algorithm, but types are small here
    eta_reduce :: TyCon -> [PredType] -> ([PredType], [TyConBinder])
eta_reduce TyCon
fam_tc [PredType]
pats
        = forall {c}.
[(PredType, VarSet, c)]
-> [VarBndr Id c] -> ([PredType], [VarBndr Id c])
go (forall a. [a] -> [a]
reverse (forall a b c. [a] -> [b] -> [c] -> [(a, b, c)]
zip3 [PredType]
pats [VarSet]
fvs_s [TyConBndrVis]
vis_s)) []
        where
          vis_s :: [TyConBndrVis]
          vis_s :: [TyConBndrVis]
vis_s = TyCon -> [PredType] -> [TyConBndrVis]
tcbVisibilities TyCon
fam_tc [PredType]
pats

          fvs_s :: [TyCoVarSet]  -- 1-1 correspondence with pats
                                 -- Each elt is the free vars of all /earlier/ pats
          (VarSet
_, [VarSet]
fvs_s) = forall (t :: * -> *) s a b.
Traversable t =>
(s -> a -> (s, b)) -> s -> t a -> (s, t b)
mapAccumL VarSet -> PredType -> (VarSet, VarSet)
add_fvs VarSet
emptyVarSet [PredType]
pats
          add_fvs :: VarSet -> PredType -> (VarSet, VarSet)
add_fvs VarSet
fvs PredType
pat = (VarSet
fvs VarSet -> VarSet -> VarSet
`unionVarSet` PredType -> VarSet
tyCoVarsOfType PredType
pat, VarSet
fvs)

    go :: [(PredType, VarSet, c)]
-> [VarBndr Id c] -> ([PredType], [VarBndr Id c])
go ((PredType
pat, VarSet
fvs_to_the_left, c
tcb_vis):[(PredType, VarSet, c)]
pats) [VarBndr Id c]
etad_tvs
      | Just Id
tv <- PredType -> Maybe Id
getTyVar_maybe PredType
pat
      , Bool -> Bool
not (Id
tv Id -> VarSet -> Bool
`elemVarSet` VarSet
fvs_to_the_left)
      = [(PredType, VarSet, c)]
-> [VarBndr Id c] -> ([PredType], [VarBndr Id c])
go [(PredType, VarSet, c)]
pats (forall var argf. var -> argf -> VarBndr var argf
Bndr Id
tv c
tcb_vis forall a. a -> [a] -> [a]
: [VarBndr Id c]
etad_tvs)
    go [(PredType, VarSet, c)]
pats [VarBndr Id c]
etad_tvs = (forall a. [a] -> [a]
reverse (forall a b. (a -> b) -> [a] -> [b]
map forall a b c. (a, b, c) -> a
fstOf3 [(PredType, VarSet, c)]
pats), [VarBndr Id c]
etad_tvs)

    -- Create a Name-TyVar mapping to bring into scope when typechecking any
    -- deriving clauses this data family instance may have.
    -- See Note [Associated data family instances and di_scoped_tvs].
    mk_deriv_info_scoped_tv_pr :: TyVar -> (Name, TyVar)
    mk_deriv_info_scoped_tv_pr :: Id -> (Name, Id)
mk_deriv_info_scoped_tv_pr Id
tv =
      let n :: Name
n = forall a. VarEnv a -> a -> Id -> a
lookupWithDefaultVarEnv TyVarEnv Name
tv_skol_env (Id -> Name
tyVarName Id
tv) Id
tv
      in (Name
n, Id
tv)

{-
Note [Associated data family instances and di_scoped_tvs]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some care is required to implement `deriving` correctly for associated data
family instances. Consider this example from #18055:

  class C a where
    data D a

  class X a b

  instance C (Maybe a) where
    data D (Maybe a) deriving (X a)

When typechecking the `X a` in `deriving (X a)`, we must ensure that the `a`
from the instance header is brought into scope. This is the role of
di_scoped_tvs, which maps from the original, renamed `a` to the skolemized,
typechecked `a`. When typechecking the `deriving` clause, this mapping will be
consulted when looking up the `a` in `X a`.

A naïve attempt at creating the di_scoped_tvs is to simply reuse the
tyConTyVars of the representation TyCon for `data D (Maybe a)`. This is only
half correct, however. We do want the typechecked `a`'s Name in the /range/
of the mapping, but we do not want it in the /domain/ of the mapping.
To ensure that the original `a`'s Name ends up in the domain, we consult a
TyVarEnv (passed as an argument to tcDataFamInstDecl) that maps from the
typechecked `a`'s Name to the original `a`'s Name. In the even that
tcDataFamInstDecl is processing a non-associated data family instance, this
TyVarEnv will simply be empty, and there is nothing to worry about.
-}

-----------------------
tcDataFamInstHeader
    :: AssocInstInfo -> TyCon -> HsOuterFamEqnTyVarBndrs GhcRn
    -> LexicalFixity -> Maybe (LHsContext GhcRn)
    -> HsTyPats GhcRn -> Maybe (LHsKind GhcRn)
    -> NewOrData
    -> TcM ([TyVar], [Type], Kind, ThetaType)
-- The "header" of a data family instance is the part other than
-- the data constructors themselves
--    e.g.  data instance D [a] :: * -> * where ...
-- Here the "header" is the bit before the "where"
tcDataFamInstHeader :: AssocInstInfo
-> TyCon
-> HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
-> LexicalFixity
-> Maybe (LHsContext (GhcPass 'Renamed))
-> HsTyPats (GhcPass 'Renamed)
-> Maybe (LHsKind (GhcPass 'Renamed))
-> NewOrData
-> TcM ([Id], [PredType], PredType, [PredType])
tcDataFamInstHeader AssocInstInfo
mb_clsinfo TyCon
fam_tc HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
outer_bndrs LexicalFixity
fixity
                    Maybe (LHsContext (GhcPass 'Renamed))
hs_ctxt HsTyPats (GhcPass 'Renamed)
hs_pats Maybe (LHsKind (GhcPass 'Renamed))
m_ksig NewOrData
new_or_data
  = do { String -> SDoc -> TcRn ()
traceTc String
"tcDataFamInstHeader {" (forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr HsTyPats (GhcPass 'Renamed)
hs_pats)
       ; (TcLevel
tclvl, WantedConstraints
wanted, ([Id]
scoped_tvs, ([PredType]
stupid_theta, PredType
lhs_ty, PredType
master_res_kind, PredType
instance_res_kind)))
            <- forall a. String -> TcM a -> TcM (TcLevel, WantedConstraints, a)
pushLevelAndSolveEqualitiesX String
"tcDataFamInstHeader" forall a b. (a -> b) -> a -> b
$
               forall a.
HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
-> TcM a -> TcM ([Id], a)
bindOuterFamEqnTKBndrs HsOuterFamEqnTyVarBndrs (GhcPass 'Renamed)
outer_bndrs                 forall a b. (a -> b) -> a -> b
$
               do { [PredType]
stupid_theta <- Maybe (LHsContext (GhcPass 'Renamed)) -> TcM [PredType]
tcHsContext Maybe (LHsContext (GhcPass 'Renamed))
hs_ctxt
                  ; (PredType
lhs_ty, PredType
lhs_kind) <- TyCon -> HsTyPats (GhcPass 'Renamed) -> TcM (PredType, PredType)
tcFamTyPats TyCon
fam_tc HsTyPats (GhcPass 'Renamed)
hs_pats
                  ; (PredType
lhs_applied_ty, PredType
lhs_applied_kind)
                      <- PredType -> PredType -> TcM (PredType, PredType)
tcInstInvisibleTyBinders PredType
lhs_ty PredType
lhs_kind
                      -- See Note [Data family/instance return kinds]
                      -- in GHC.Tc.TyCl point (DF3)

                  -- Ensure that the instance is consistent
                  -- with its parent class
                  ; AssocInstInfo -> PredType -> TcRn ()
addConsistencyConstraints AssocInstInfo
mb_clsinfo PredType
lhs_ty

                  -- Add constraints from the result signature
                  ; PredType
res_kind <- Maybe (GenLocated SrcSpanAnnA (HsType (GhcPass 'Renamed)))
-> TcM PredType
tc_kind_sig Maybe (LHsKind (GhcPass 'Renamed))
m_ksig

                  -- Do not add constraints from the data constructors
                  -- See Note [Kind inference for data family instances]

                  -- Check that the result kind of the TyCon applied to its args
                  -- is compatible with the explicit signature (or Type, if there
                  -- is none)
                  ; let hs_lhs :: LHsKind (GhcPass 'Renamed)
hs_lhs = forall (p :: Pass) a.
IsSrcSpanAnn p a =>
LexicalFixity
-> IdP (GhcPass p)
-> [LHsTypeArg (GhcPass p)]
-> LHsType (GhcPass p)
nlHsTyConApp LexicalFixity
fixity (forall a. NamedThing a => a -> Name
getName TyCon
fam_tc) HsTyPats (GhcPass 'Renamed)
hs_pats
                  ; CoercionN
_ <- Maybe SDoc -> PredType -> PredType -> TcM CoercionN
unifyKind (forall a. a -> Maybe a
Just (forall a. Outputable a => a -> SDoc
ppr LHsKind (GhcPass 'Renamed)
hs_lhs)) PredType
lhs_applied_kind PredType
res_kind

                  ; String -> SDoc -> TcRn ()
traceTc String
"tcDataFamInstHeader" forall a b. (a -> b) -> a -> b
$
                    [SDoc] -> SDoc
vcat [ forall a. Outputable a => a -> SDoc
ppr TyCon
fam_tc, forall a. Outputable a => a -> SDoc
ppr Maybe (LHsKind (GhcPass 'Renamed))
m_ksig, forall a. Outputable a => a -> SDoc
ppr PredType
lhs_applied_kind, forall a. Outputable a => a -> SDoc
ppr PredType
res_kind ]
                  ; forall (m :: * -> *) a. Monad m => a -> m a
return ( [PredType]
stupid_theta
                           , PredType
lhs_applied_ty
                           , PredType
lhs_applied_kind
                           , PredType
res_kind ) }

       -- This code (and the stuff immediately above) is very similar
       -- to that in tcTyFamInstEqnGuts.  Maybe we should abstract the
       -- common code; but for the moment I concluded that it's
       -- clearer to duplicate it.  Still, if you fix a bug here,
       -- check there too!

       -- See GHC.Tc.TyCl Note [Generalising in tcFamTyPatsGuts]
       ; CandidatesQTvs
dvs  <- [PredType] -> TcM CandidatesQTvs
candidateQTyVarsOfTypes (PredType
lhs_ty forall a. a -> [a] -> [a]
: [Id] -> [PredType]
mkTyVarTys [Id]
scoped_tvs)
       ; [Id]
qtvs <- CandidatesQTvs -> TcM [Id]
quantifyTyVars CandidatesQTvs
dvs
       ; SkolemInfo -> [Id] -> TcLevel -> WantedConstraints -> TcRn ()
reportUnsolvedEqualities SkolemInfo
FamInstSkol [Id]
qtvs TcLevel
tclvl WantedConstraints
wanted

       -- Zonk the patterns etc into the Type world
       ; ZonkEnv
ze           <- ZonkFlexi -> TcM ZonkEnv
mkEmptyZonkEnv ZonkFlexi
NoFlexi
       ; (ZonkEnv
ze, [Id]
qtvs)   <- ZonkEnv -> [Id] -> TcM (ZonkEnv, [Id])
zonkTyBndrsX           ZonkEnv
ze [Id]
qtvs
       ; PredType
lhs_ty       <- ZonkEnv -> PredType -> TcM PredType
zonkTcTypeToTypeX      ZonkEnv
ze PredType
lhs_ty
       ; [PredType]
stupid_theta <- ZonkEnv -> [PredType] -> TcM [PredType]
zonkTcTypesToTypesX    ZonkEnv
ze [PredType]
stupid_theta
       ; PredType
master_res_kind   <- ZonkEnv -> PredType -> TcM PredType
zonkTcTypeToTypeX ZonkEnv
ze PredType
master_res_kind
       ; PredType
instance_res_kind <- ZonkEnv -> PredType -> TcM PredType
zonkTcTypeToTypeX ZonkEnv
ze PredType
instance_res_kind

       -- We check that res_kind is OK with checkDataKindSig in
       -- tcDataFamInstDecl, after eta-expansion.  We need to check that
       -- it's ok because res_kind can come from a user-written kind signature.
       -- See Note [Datatype return kinds], point (4a)

       ; DataSort -> PredType -> TcRn ()
checkDataKindSig (NewOrData -> DataSort
DataInstanceSort NewOrData
new_or_data) PredType
master_res_kind
       ; DataSort -> PredType -> TcRn ()
checkDataKindSig (NewOrData -> DataSort
DataInstanceSort NewOrData
new_or_data) PredType
instance_res_kind

       -- Check that type patterns match the class instance head
       -- The call to splitTyConApp_maybe here is just an inlining of
       -- the body of unravelFamInstPats.
       ; [PredType]
pats <- case HasDebugCallStack => PredType -> Maybe (TyCon, [PredType])
splitTyConApp_maybe PredType
lhs_ty of
           Just (TyCon
_, [PredType]
pats) -> forall (f :: * -> *) a. Applicative f => a -> f a
pure [PredType]
pats
           Maybe (TyCon, [PredType])
Nothing -> forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"tcDataFamInstHeader" (forall a. Outputable a => a -> SDoc
ppr PredType
lhs_ty)

       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([Id]
qtvs, [PredType]
pats, PredType
master_res_kind, [PredType]
stupid_theta) }
  where
    fam_name :: Name
fam_name  = TyCon -> Name
tyConName TyCon
fam_tc
    data_ctxt :: UserTypeCtxt
data_ctxt = Name -> UserTypeCtxt
DataKindCtxt Name
fam_name

    -- See Note [Implementation of UnliftedNewtypes] in GHC.Tc.TyCl, families (2),
    -- and Note [Implementation of UnliftedDatatypes].
    tc_kind_sig :: Maybe (GenLocated SrcSpanAnnA (HsType (GhcPass 'Renamed)))
-> TcM PredType
tc_kind_sig Maybe (GenLocated SrcSpanAnnA (HsType (GhcPass 'Renamed)))
Nothing
      = do { Bool
unlifted_newtypes  <- forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.UnliftedNewtypes
           ; Bool
unlifted_datatypes <- forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.UnliftedDatatypes
           ; case NewOrData
new_or_data of
               NewOrData
NewType  | Bool
unlifted_newtypes  -> TcM PredType
newOpenTypeKind
               NewOrData
DataType | Bool
unlifted_datatypes -> TcM PredType
newOpenTypeKind
               NewOrData
_                             -> forall (f :: * -> *) a. Applicative f => a -> f a
pure PredType
liftedTypeKind
           }

    -- See Note [Result kind signature for a data family instance]
    tc_kind_sig (Just GenLocated SrcSpanAnnA (HsType (GhcPass 'Renamed))
hs_kind)
      = do { PredType
sig_kind <- UserTypeCtxt -> LHsKind (GhcPass 'Renamed) -> TcM PredType
tcLHsKindSig UserTypeCtxt
data_ctxt GenLocated SrcSpanAnnA (HsType (GhcPass 'Renamed))
hs_kind
           ; TcLevel
lvl <- TcM TcLevel
getTcLevel
           ; let ([Id]
tvs, PredType
inner_kind) = PredType -> ([Id], PredType)
tcSplitForAllInvisTyVars PredType
sig_kind
           ; (TCvSubst
subst, [Id]
_tvs') <- TcLevel -> Bool -> TCvSubst -> [Id] -> TcM (TCvSubst, [Id])
tcInstSkolTyVarsAt TcLevel
lvl Bool
False TCvSubst
emptyTCvSubst [Id]
tvs
             -- Perhaps surprisingly, we don't need the skolemised tvs themselves
           ; forall (m :: * -> *) a. Monad m => a -> m a
return (HasCallStack => TCvSubst -> PredType -> PredType
substTy TCvSubst
subst PredType
inner_kind) }

{- Note [Result kind signature for a data family instance]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The expected type might have a forall at the type. Normally, we
can't skolemise in kinds because we don't have type-level lambda.
But here, we're at the top-level of an instance declaration, so
we actually have a place to put the regeneralised variables.
Thus: skolemise away. cf. GHC.Tc.Utils.Unify.tcTopSkolemise
Examples in indexed-types/should_compile/T12369

Note [Implementing eta reduction for data families]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   data D :: * -> * -> * -> * -> *

   data instance D [(a,b)] p q :: * -> * where
      D1 :: blah1
      D2 :: blah2

Then we'll generate a representation data type
  data Drep a b p q z where
      D1 :: blah1
      D2 :: blah2

and an axiom to connect them
  axiom AxDrep forall a b p q z. D [(a,b]] p q z = Drep a b p q z

except that we'll eta-reduce the axiom to
  axiom AxDrep forall a b. D [(a,b]] = Drep a b

This is described at some length in Note [Eta reduction for data families]
in GHC.Core.Coercion.Axiom. There are several fiddly subtleties lurking here,
however, so this Note aims to describe these subtleties:

* The representation tycon Drep is parameterised over the free
  variables of the pattern, in no particular order. So there is no
  guarantee that 'p' and 'q' will come last in Drep's parameters, and
  in the right order.  So, if the /patterns/ of the family instance
  are eta-reducible, we re-order Drep's parameters to put the
  eta-reduced type variables last.

* Although we eta-reduce the axiom, we eta-/expand/ the representation
  tycon Drep.  The kind of D says it takes four arguments, but the
  data instance header only supplies three.  But the AlgTyCon for Drep
  itself must have enough TyConBinders so that its result kind is Type.
  So, with etaExpandAlgTyCon we make up some extra TyConBinders.
  See point (3) in Note [Datatype return kinds] in GHC.Tc.TyCl.

* The result kind in the instance might be a polykind, like this:
     data family DP a :: forall k. k -> *
     data instance DP [b] :: forall k1 k2. (k1,k2) -> *

  So in type-checking the LHS (DP Int) we need to check that it is
  more polymorphic than the signature.  To do that we must skolemise
  the signature and instantiate the call of DP.  So we end up with
     data instance DP [b] @(k1,k2) (z :: (k1,k2)) where

  Note that we must parameterise the representation tycon DPrep over
  'k1' and 'k2', as well as 'b'.

  The skolemise bit is done in tc_kind_sig, while the instantiate bit
  is done by tcFamTyPats.

* Very fiddly point.  When we eta-reduce to
     axiom AxDrep forall a b. D [(a,b]] = Drep a b

  we want the kind of (D [(a,b)]) to be the same as the kind of
  (Drep a b).  This ensures that applying the axiom doesn't change the
  kind.  Why is that hard?  Because the kind of (Drep a b) depends on
  the TyConBndrVis on Drep's arguments. In particular do we have
    (forall (k::*). blah) or (* -> blah)?

  We must match whatever D does!  In #15817 we had
      data family X a :: forall k. * -> *   -- Note: a forall that is not used
      data instance X Int b = MkX

  So the data instance is really
      data istance X Int @k b = MkX

  The axiom will look like
      axiom    X Int = Xrep

  and it's important that XRep :: forall k * -> *, following X.

  To achieve this we get the TyConBndrVis flags from tcbVisibilities,
  and use those flags for any eta-reduced arguments.  Sigh.

* The final turn of the knife is that tcbVisibilities is itself
  tricky to sort out.  Consider
      data family D k :: k
  Then consider D (forall k2. k2 -> k2) Type Type
  The visibility flags on an application of D may affected by the arguments
  themselves.  Heavy sigh.  But not truly hard; that's what tcbVisibilities
  does.

Note [Kind inference for data family instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this GADT-style data type declaration, where I have used
fresh variables in the data constructor's type, to stress that c,d are
quite distinct from a,b.
   data T a b where
     MkT :: forall c d. c d -> T c d

Following Note [Inferring kinds for type declarations] in GHC.Tc.TyCl,
to infer T's kind, we initially give T :: kappa, a monomorpic kind,
gather constraints from the header and data constructors, and conclude
   T :: (kappa1 -> type) -> kappa1 -> Type
Then we generalise, giving
   T :: forall k. (k->Type) -> k -> Type

Now what about a data /instance/ decl
   data family T :: forall k. (k->Type) -> k -> Type

   data instance T p Int where ...

No doubt here! The poly-kinded T is instantiated with k=Type, so the
header really looks like
   data instance T @Type (p :: Type->Type) Int where ...

But what about this?
   data instance T p q where
      MkT :: forall r. r Int -> T r Int

So what kind do 'p' and 'q' have?  No clues from the header, but from
the data constructor we can clearly see that (r :: Type->Type).  Does
that mean that the the /entire data instance/ is instantiated at Type,
like this?
   data instance T @Type (p :: Type->Type) (q :: Type) where
      ...

Not at all! This is a /GADT/-style decl, so the kind argument might
be specialised in this particular data constructor, thus:
   data instance T @k (p :: k->Type) (q :: k) where
     MkT :: forall (r :: Type -> Type).
            r Int -> T @Type r Int
(and perhaps specialised differently in some other data
constructor MkT2).

The key difference in this case and 'data T' at the top of this Note
is that we have no known kind for 'data T'. We thus forbid different
specialisations of T in its constructors, in an attempt to avoid
inferring polymorphic recursion. In data family T, however, there is
no problem with polymorphic recursion: we already /fully know/ T's
kind -- that came from the family declaration, and is not influenced
by the data instances -- and hence we /can/ specialise T's kind
differently in different GADT data constructors.

SHORT SUMMARY: in a data instance decl, it's not clear whether kind
constraints arising from the data constructors should be considered
local to the (GADT) data /constructor/ or should apply to the entire
data instance.

DESIGN CHOICE: in data/newtype family instance declarations, we ignore
the /data constructor/ declarations altogether, looking only at the
data instance /header/.

Observations:
* This choice is simple to describe, as well as simple to implement.
  For a data/newtype instance decl, the instance kinds are influenced
  /only/ by the header.

* We could treat Haskell-98 style data-instance decls differently, by
  taking the data constructors into account, since there are no GADT
  issues.  But we don't, for simplicity, and because it means you can
  understand the data type instance by looking only at the header.

* Newtypes can be declared in GADT syntax, but they can't do GADT-style
  specialisation, so like Haskell-98 definitions we could take the
  data constructors into account.  Again we don't, for the same reason.

So for now at least, we keep the simplest choice. See #18891 and !4419
for more discussion of this issue.

Kind inference for data types (Xie et al) https://arxiv.org/abs/1911.06153
takes a slightly different approach.
-}


{- *********************************************************************
*                                                                      *
      Class instance declarations, pass 2
*                                                                      *
********************************************************************* -}

tcInstDecls2 :: [LTyClDecl GhcRn] -> [InstInfo GhcRn]
             -> TcM (LHsBinds GhcTc)
-- (a) From each class declaration,
--      generate any default-method bindings
-- (b) From each instance decl
--      generate the dfun binding

tcInstDecls2 :: [LTyClDecl (GhcPass 'Renamed)]
-> [InstInfo (GhcPass 'Renamed)] -> TcM (LHsBinds GhcTc)
tcInstDecls2 [LTyClDecl (GhcPass 'Renamed)]
tycl_decls [InstInfo (GhcPass 'Renamed)]
inst_decls
  = do  { -- (a) Default methods from class decls
          let class_decls :: [GenLocated SrcSpanAnnA (TyClDecl (GhcPass 'Renamed))]
class_decls = forall a. (a -> Bool) -> [a] -> [a]
filter (forall pass. TyClDecl pass -> Bool
isClassDecl forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall l e. GenLocated l e -> e
unLoc) [LTyClDecl (GhcPass 'Renamed)]
tycl_decls
        ; [Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))]
dm_binds_s <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM LTyClDecl (GhcPass 'Renamed) -> TcM (LHsBinds GhcTc)
tcClassDecl2 [GenLocated SrcSpanAnnA (TyClDecl (GhcPass 'Renamed))]
class_decls
        ; let dm_binds :: Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
dm_binds = forall a. [Bag a] -> Bag a
unionManyBags [Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))]
dm_binds_s

          -- (b) instance declarations
        ; let dm_ids :: [IdP GhcTc]
dm_ids = forall p idR.
CollectPass p =>
CollectFlag p -> LHsBindsLR p idR -> [IdP p]
collectHsBindsBinders forall p. CollectFlag p
CollNoDictBinders Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
dm_binds
              -- Add the default method Ids (again)
              -- (they were already added in GHC.Tc.TyCl.Utils.tcAddImplicits)
              -- See Note [Default methods in the type environment]
        ; [Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))]
inst_binds_s <- forall r. [Id] -> TcM r -> TcM r
tcExtendGlobalValEnv [IdP GhcTc]
dm_ids forall a b. (a -> b) -> a -> b
$
                          forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM InstInfo (GhcPass 'Renamed) -> TcM (LHsBinds GhcTc)
tcInstDecl2 [InstInfo (GhcPass 'Renamed)]
inst_decls

          -- Done
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
dm_binds forall a. Bag a -> Bag a -> Bag a
`unionBags` forall a. [Bag a] -> Bag a
unionManyBags [Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))]
inst_binds_s) }

{- Note [Default methods in the type environment]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The default method Ids are already in the type environment (see Note
[Default method Ids and Template Haskell] in TcTyDcls), BUT they
don't have their InlinePragmas yet.  Usually that would not matter,
because the simplifier propagates information from binding site to
use.  But, unusually, when compiling instance decls we *copy* the
INLINE pragma from the default method to the method for that
particular operation (see Note [INLINE and default methods] below).

So right here in tcInstDecls2 we must re-extend the type envt with
the default method Ids replete with their INLINE pragmas.  Urk.
-}

tcInstDecl2 :: InstInfo GhcRn -> TcM (LHsBinds GhcTc)
            -- Returns a binding for the dfun
tcInstDecl2 :: InstInfo (GhcPass 'Renamed) -> TcM (LHsBinds GhcTc)
tcInstDecl2 (InstInfo { iSpec :: forall a. InstInfo a -> ClsInst
iSpec = ClsInst
ispec, iBinds :: forall a. InstInfo a -> InstBindings a
iBinds = InstBindings (GhcPass 'Renamed)
ibinds })
  = forall r. TcRn r -> TcRn r -> TcRn r
recoverM (forall (m :: * -> *) a. Monad m => a -> m a
return forall (idL :: Pass) idR. LHsBindsLR (GhcPass idL) idR
emptyLHsBinds)             forall a b. (a -> b) -> a -> b
$
    forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan SrcSpan
loc                              forall a b. (a -> b) -> a -> b
$
    forall a. SDoc -> TcM a -> TcM a
addErrCtxt (PredType -> SDoc
instDeclCtxt2 (Id -> PredType
idType Id
dfun_id)) forall a b. (a -> b) -> a -> b
$
    do {  -- Instantiate the instance decl with skolem constants
       ; ([Id]
inst_tyvars, [PredType]
dfun_theta, PredType
inst_head) <- Id -> TcM ([Id], [PredType], PredType)
tcSkolDFunType Id
dfun_id
       ; [Id]
dfun_ev_vars <- [PredType] -> TcM [Id]
newEvVars [PredType]
dfun_theta
                     -- We instantiate the dfun_id with superSkolems.
                     -- See Note [Subtle interaction of recursion and overlap]
                     -- and Note [Binding when looking up instances]

       ; let (Class
clas, [PredType]
inst_tys) = PredType -> (Class, [PredType])
tcSplitDFunHead PredType
inst_head
             ([Id]
class_tyvars, [PredType]
sc_theta, [Id]
_, [ClassOpItem]
op_items) = Class -> ([Id], [PredType], [Id], [ClassOpItem])
classBigSig Class
clas
             sc_theta' :: [PredType]
sc_theta' = HasCallStack => TCvSubst -> [PredType] -> [PredType]
substTheta (HasDebugCallStack => [Id] -> [PredType] -> TCvSubst
zipTvSubst [Id]
class_tyvars [PredType]
inst_tys) [PredType]
sc_theta

       ; String -> SDoc -> TcRn ()
traceTc String
"tcInstDecl2" ([SDoc] -> SDoc
vcat [forall a. Outputable a => a -> SDoc
ppr [Id]
inst_tyvars, forall a. Outputable a => a -> SDoc
ppr [PredType]
inst_tys, forall a. Outputable a => a -> SDoc
ppr [PredType]
dfun_theta, forall a. Outputable a => a -> SDoc
ppr [PredType]
sc_theta'])

                      -- Deal with 'SPECIALISE instance' pragmas
                      -- See Note [SPECIALISE instance pragmas]
       ; spec_inst_info :: ([LTcSpecPrag],
 NameEnv [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))])
spec_inst_info@([LTcSpecPrag]
spec_inst_prags,NameEnv [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
_) <- Id
-> InstBindings (GhcPass 'Renamed)
-> TcM ([LTcSpecPrag], TcPragEnv)
tcSpecInstPrags Id
dfun_id InstBindings (GhcPass 'Renamed)
ibinds

         -- Typecheck superclasses and methods
         -- See Note [Typechecking plan for instance declarations]
       ; EvBindsVar
dfun_ev_binds_var <- TcM EvBindsVar
newTcEvBinds
       ; let dfun_ev_binds :: TcEvBinds
dfun_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
dfun_ev_binds_var
       ; (TcLevel
tclvl, ([Id]
sc_meth_ids, Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
sc_meth_binds, Bag Implication
sc_meth_implics))
             <- forall a. TcM a -> TcM (TcLevel, a)
pushTcLevelM forall a b. (a -> b) -> a -> b
$
                do { ([Id]
sc_ids, Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
sc_binds, Bag Implication
sc_implics)
                        <- Id
-> Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> [PredType]
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcSuperClasses Id
dfun_id Class
clas [Id]
inst_tyvars [Id]
dfun_ev_vars
                                          [PredType]
inst_tys TcEvBinds
dfun_ev_binds
                                          [PredType]
sc_theta'

                      -- Typecheck the methods
                   ; ([Id]
meth_ids, Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
meth_binds, Bag Implication
meth_implics)
                        <- Id
-> Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> ([LTcSpecPrag], TcPragEnv)
-> [ClassOpItem]
-> InstBindings (GhcPass 'Renamed)
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcMethods Id
dfun_id Class
clas [Id]
inst_tyvars [Id]
dfun_ev_vars
                                     [PredType]
inst_tys TcEvBinds
dfun_ev_binds ([LTcSpecPrag],
 NameEnv [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))])
spec_inst_info
                                     [ClassOpItem]
op_items InstBindings (GhcPass 'Renamed)
ibinds

                   ; forall (m :: * -> *) a. Monad m => a -> m a
return ( [Id]
sc_ids     forall a. [a] -> [a] -> [a]
++          [Id]
meth_ids
                            , Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
sc_binds   forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
meth_binds
                            , Bag Implication
sc_implics forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag Implication
meth_implics ) }

       ; Implication
imp <- TcM Implication
newImplication
       ; Implication -> TcRn ()
emitImplication forall a b. (a -> b) -> a -> b
$
         Implication
imp { ic_tclvl :: TcLevel
ic_tclvl  = TcLevel
tclvl
             , ic_skols :: [Id]
ic_skols  = [Id]
inst_tyvars
             , ic_given :: [Id]
ic_given  = [Id]
dfun_ev_vars
             , ic_wanted :: WantedConstraints
ic_wanted = Bag Implication -> WantedConstraints
mkImplicWC Bag Implication
sc_meth_implics
             , ic_binds :: EvBindsVar
ic_binds  = EvBindsVar
dfun_ev_binds_var
             , ic_info :: SkolemInfo
ic_info   = SkolemInfo
InstSkol }

       -- Create the result bindings
       ; Id
self_dict <- Class -> [PredType] -> TcM Id
newDict Class
clas [PredType]
inst_tys
       ; let class_tc :: TyCon
class_tc      = Class -> TyCon
classTyCon Class
clas
             loc' :: SrcSpanAnnA
loc'          = forall ann. SrcSpan -> SrcAnn ann
noAnnSrcSpan SrcSpan
loc
             [DataCon
dict_constr] = TyCon -> [DataCon]
tyConDataCons TyCon
class_tc
             dict_bind :: LHsBind GhcTc
dict_bind = forall (p :: Pass).
IdP (GhcPass p) -> LHsExpr (GhcPass p) -> LHsBind (GhcPass p)
mkVarBind Id
self_dict (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' HsExpr GhcTc
con_app_args)

                     -- We don't produce a binding for the dict_constr; instead we
                     -- rely on the simplifier to unfold this saturated application
                     -- We do this rather than generate an HsCon directly, because
                     -- it means that the special cases (e.g. dictionary with only one
                     -- member) are dealt with by the common MkId.mkDataConWrapId
                     -- code rather than needing to be repeated here.
                     --    con_app_tys  = MkD ty1 ty2
                     --    con_app_scs  = MkD ty1 ty2 sc1 sc2
                     --    con_app_args = MkD ty1 ty2 sc1 sc2 op1 op2
             con_app_tys :: HsExpr GhcTc
con_app_tys  = HsWrapper -> HsExpr GhcTc -> HsExpr GhcTc
mkHsWrap ([PredType] -> HsWrapper
mkWpTyApps [PredType]
inst_tys)
                                  (forall p. XConLikeOut p -> ConLike -> HsExpr p
HsConLikeOut NoExtField
noExtField (DataCon -> ConLike
RealDataCon DataCon
dict_constr))
                       -- NB: We *can* have covars in inst_tys, in the case of
                       -- promoted GADT constructors.

             con_app_args :: HsExpr GhcTc
con_app_args = forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' HsExpr GhcTc -> Id -> HsExpr GhcTc
app_to_meth HsExpr GhcTc
con_app_tys [Id]
sc_meth_ids

             app_to_meth :: HsExpr GhcTc -> Id -> HsExpr GhcTc
             app_to_meth :: HsExpr GhcTc -> Id -> HsExpr GhcTc
app_to_meth HsExpr GhcTc
fun Id
meth_id = forall p. XApp p -> LHsExpr p -> LHsExpr p -> HsExpr p
HsApp EpAnnCO
noComments (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' HsExpr GhcTc
fun)
                                            (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' (HsWrapper -> Id -> HsExpr GhcTc
wrapId HsWrapper
arg_wrapper Id
meth_id))

             inst_tv_tys :: [PredType]
inst_tv_tys = [Id] -> [PredType]
mkTyVarTys [Id]
inst_tyvars
             arg_wrapper :: HsWrapper
arg_wrapper = [Id] -> HsWrapper
mkWpEvVarApps [Id]
dfun_ev_vars HsWrapper -> HsWrapper -> HsWrapper
<.> [PredType] -> HsWrapper
mkWpTyApps [PredType]
inst_tv_tys

             is_newtype :: Bool
is_newtype = TyCon -> Bool
isNewTyCon TyCon
class_tc
             dfun_id_w_prags :: Id
dfun_id_w_prags = Id -> [Id] -> Id
addDFunPrags Id
dfun_id [Id]
sc_meth_ids
             dfun_spec_prags :: TcSpecPrags
dfun_spec_prags
                | Bool
is_newtype = [LTcSpecPrag] -> TcSpecPrags
SpecPrags []
                | Bool
otherwise  = [LTcSpecPrag] -> TcSpecPrags
SpecPrags [LTcSpecPrag]
spec_inst_prags
                    -- Newtype dfuns just inline unconditionally,
                    -- so don't attempt to specialise them

             export :: ABExport GhcTc
export = ABE { abe_ext :: XABE GhcTc
abe_ext  = NoExtField
noExtField
                          , abe_wrap :: HsWrapper
abe_wrap = HsWrapper
idHsWrapper
                          , abe_poly :: IdP GhcTc
abe_poly = Id
dfun_id_w_prags
                          , abe_mono :: IdP GhcTc
abe_mono = Id
self_dict
                          , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
dfun_spec_prags }
                          -- NB: see Note [SPECIALISE instance pragmas]
             main_bind :: HsBindLR GhcTc GhcTc
main_bind = AbsBinds { abs_ext :: XAbsBinds GhcTc GhcTc
abs_ext = NoExtField
noExtField
                                  , abs_tvs :: [Id]
abs_tvs = [Id]
inst_tyvars
                                  , abs_ev_vars :: [Id]
abs_ev_vars = [Id]
dfun_ev_vars
                                  , abs_exports :: [ABExport GhcTc]
abs_exports = [ABExport GhcTc
export]
                                  , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = []
                                  , abs_binds :: LHsBinds GhcTc
abs_binds = forall a. a -> Bag a
unitBag LHsBind GhcTc
dict_bind
                                  , abs_sig :: Bool
abs_sig = Bool
True }

       ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall a. a -> Bag a
unitBag (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
loc' HsBindLR GhcTc GhcTc
main_bind)
                  forall a. Bag a -> Bag a -> Bag a
`unionBags` Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
sc_meth_binds)
       }
 where
   dfun_id :: Id
dfun_id = ClsInst -> Id
instanceDFunId ClsInst
ispec
   loc :: SrcSpan
loc     = forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id

addDFunPrags :: DFunId -> [Id] -> DFunId
-- DFuns need a special Unfolding and InlinePrag
--    See Note [ClassOp/DFun selection]
--    and Note [Single-method classes]
-- It's easiest to create those unfoldings right here, where
-- have all the pieces in hand, even though we are messing with
-- Core at this point, which the typechecker doesn't usually do
-- However we take care to build the unfolding using the TyVars from
-- the DFunId rather than from the skolem pieces that the typechecker
-- is messing with.
addDFunPrags :: Id -> [Id] -> Id
addDFunPrags Id
dfun_id [Id]
sc_meth_ids
 | Bool
is_newtype
  = Id
dfun_id Id -> Unfolding -> Id
`setIdUnfolding`  Int -> SimpleOpts -> CoreExpr -> Unfolding
mkInlineUnfoldingWithArity Int
0 SimpleOpts
defaultSimpleOpts CoreExpr
con_app
            Id -> InlinePragma -> Id
`setInlinePragma` InlinePragma
alwaysInlinePragma { inl_sat :: Maybe Int
inl_sat = forall a. a -> Maybe a
Just Int
0 }
 | Bool
otherwise
 = Id
dfun_id Id -> Unfolding -> Id
`setIdUnfolding`  [Id] -> DataCon -> [CoreExpr] -> Unfolding
mkDFunUnfolding [Id]
dfun_bndrs DataCon
dict_con [CoreExpr]
dict_args
           Id -> InlinePragma -> Id
`setInlinePragma` InlinePragma
dfunInlinePragma
 where
   con_app :: CoreExpr
con_app    = forall b. [b] -> Expr b -> Expr b
mkLams [Id]
dfun_bndrs forall a b. (a -> b) -> a -> b
$
                forall b. Expr b -> [Expr b] -> Expr b
mkApps (forall b. Id -> Expr b
Var (DataCon -> Id
dataConWrapId DataCon
dict_con)) [CoreExpr]
dict_args
                 -- mkApps is OK because of the checkForLevPoly call in checkValidClass
                 -- See Note [Levity polymorphism checking] in GHC.HsToCore.Monad
   dict_args :: [CoreExpr]
dict_args  = forall a b. (a -> b) -> [a] -> [b]
map forall b. PredType -> Expr b
Type [PredType]
inst_tys forall a. [a] -> [a] -> [a]
++
                [forall b. Expr b -> [Id] -> Expr b
mkVarApps (forall b. Id -> Expr b
Var Id
id) [Id]
dfun_bndrs | Id
id <- [Id]
sc_meth_ids]

   ([Id]
dfun_tvs, [PredType]
dfun_theta, Class
clas, [PredType]
inst_tys) = PredType -> ([Id], [PredType], Class, [PredType])
tcSplitDFunTy (Id -> PredType
idType Id
dfun_id)
   ev_ids :: [Id]
ev_ids      = Int -> [PredType] -> [Id]
mkTemplateLocalsNum Int
1                    [PredType]
dfun_theta
   dfun_bndrs :: [Id]
dfun_bndrs  = [Id]
dfun_tvs forall a. [a] -> [a] -> [a]
++ [Id]
ev_ids
   clas_tc :: TyCon
clas_tc     = Class -> TyCon
classTyCon Class
clas
   [DataCon
dict_con]  = TyCon -> [DataCon]
tyConDataCons TyCon
clas_tc
   is_newtype :: Bool
is_newtype  = TyCon -> Bool
isNewTyCon TyCon
clas_tc

wrapId :: HsWrapper -> Id -> HsExpr GhcTc
wrapId :: HsWrapper -> Id -> HsExpr GhcTc
wrapId HsWrapper
wrapper Id
id = HsWrapper -> HsExpr GhcTc -> HsExpr GhcTc
mkHsWrap HsWrapper
wrapper (forall p. XVar p -> LIdP p -> HsExpr p
HsVar NoExtField
noExtField (forall a an. a -> LocatedAn an a
noLocA Id
id))

{- Note [Typechecking plan for instance declarations]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For instance declarations we generate the following bindings and implication
constraints.  Example:

   instance Ord a => Ord [a] where compare = <compare-rhs>

generates this:

   Bindings:
      -- Method bindings
      $ccompare :: forall a. Ord a => a -> a -> Ordering
      $ccompare = /\a \(d:Ord a). let <meth-ev-binds> in ...

      -- Superclass bindings
      $cp1Ord :: forall a. Ord a => Eq [a]
      $cp1Ord = /\a \(d:Ord a). let <sc-ev-binds>
               in dfEqList (dw :: Eq a)

   Constraints:
      forall a. Ord a =>
                -- Method constraint
             (forall. (empty) => <constraints from compare-rhs>)
                -- Superclass constraint
          /\ (forall. (empty) => dw :: Eq a)

Notice that

 * Per-meth/sc implication.  There is one inner implication per
   superclass or method, with no skolem variables or givens.  The only
   reason for this one is to gather the evidence bindings privately
   for this superclass or method.  This implication is generated
   by checkInstConstraints.

 * Overall instance implication. There is an overall enclosing
   implication for the whole instance declaration, with the expected
   skolems and givens.  We need this to get the correct "redundant
   constraint" warnings, gathering all the uses from all the methods
   and superclasses.  See GHC.Tc.Solver Note [Tracking redundant
   constraints]

 * The given constraints in the outer implication may generate
   evidence, notably by superclass selection.  Since the method and
   superclass bindings are top-level, we want that evidence copied
   into *every* method or superclass definition.  (Some of it will
   be usused in some, but dead-code elimination will drop it.)

   We achieve this by putting the evidence variable for the overall
   instance implication into the AbsBinds for each method/superclass.
   Hence the 'dfun_ev_binds' passed into tcMethods and tcSuperClasses.
   (And that in turn is why the abs_ev_binds field of AbBinds is a
   [TcEvBinds] rather than simply TcEvBinds.

   This is a bit of a hack, but works very nicely in practice.

 * Note that if a method has a locally-polymorphic binding, there will
   be yet another implication for that, generated by tcPolyCheck
   in tcMethodBody. E.g.
          class C a where
            foo :: forall b. Ord b => blah


************************************************************************
*                                                                      *
      Type-checking superclasses
*                                                                      *
************************************************************************
-}

tcSuperClasses :: DFunId -> Class -> [TcTyVar] -> [EvVar] -> [TcType]
               -> TcEvBinds
               -> TcThetaType
               -> TcM ([EvVar], LHsBinds GhcTc, Bag Implication)
-- Make a new top-level function binding for each superclass,
-- something like
--    $Ordp1 :: forall a. Ord a => Eq [a]
--    $Ordp1 = /\a \(d:Ord a). dfunEqList a (sc_sel d)
--
-- See Note [Recursive superclasses] for why this is so hard!
-- In effect, we build a special-purpose solver for the first step
-- of solving each superclass constraint
tcSuperClasses :: Id
-> Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> [PredType]
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcSuperClasses Id
dfun_id Class
cls [Id]
tyvars [Id]
dfun_evs [PredType]
inst_tys TcEvBinds
dfun_ev_binds [PredType]
sc_theta
  = do { ([Id]
ids, [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
binds, [Implication]
implics) <- forall (m :: * -> *) a b c d.
Monad m =>
(a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])
mapAndUnzip3M (PredType, Int)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc), Implication)
tc_super (forall a b. [a] -> [b] -> [(a, b)]
zip [PredType]
sc_theta [Int
fIRST_TAG..])
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([Id]
ids, forall a. [a] -> Bag a
listToBag [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
binds, forall a. [a] -> Bag a
listToBag [Implication]
implics) }
  where
    loc :: SrcSpan
loc = forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id
    size :: TypeSize
size = [PredType] -> TypeSize
sizeTypes [PredType]
inst_tys
    tc_super :: (PredType, Int)
-> IOEnv
     (Env TcGblEnv TcLclEnv)
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc), Implication)
tc_super (PredType
sc_pred, Int
n)
      = do { (Implication
sc_implic, EvBindsVar
ev_binds_var, EvTerm
sc_ev_tm)
                <- forall result. TcM result -> TcM (Implication, EvBindsVar, result)
checkInstConstraints forall a b. (a -> b) -> a -> b
$ CtOrigin -> PredType -> TcM EvTerm
emitWanted (TypeSize -> CtOrigin
ScOrigin TypeSize
size) PredType
sc_pred

           ; Name
sc_top_name  <- OccName -> TcM Name
newName (Int -> OccName -> OccName
mkSuperDictAuxOcc Int
n (forall a. NamedThing a => a -> OccName
getOccName Class
cls))
           ; Id
sc_ev_id     <- forall gbl lcl. PredType -> TcRnIf gbl lcl Id
newEvVar PredType
sc_pred
           ; EvBindsVar -> EvBind -> TcRn ()
addTcEvBind EvBindsVar
ev_binds_var forall a b. (a -> b) -> a -> b
$ Id -> EvTerm -> EvBind
mkWantedEvBind Id
sc_ev_id EvTerm
sc_ev_tm
           ; let sc_top_ty :: PredType
sc_top_ty = [Id] -> PredType -> PredType
mkInfForAllTys [Id]
tyvars forall a b. (a -> b) -> a -> b
$
                             [PredType] -> PredType -> PredType
mkPhiTy (forall a b. (a -> b) -> [a] -> [b]
map Id -> PredType
idType [Id]
dfun_evs) PredType
sc_pred
                 sc_top_id :: Id
sc_top_id = HasDebugCallStack => Name -> PredType -> PredType -> Id
mkLocalId Name
sc_top_name PredType
Many PredType
sc_top_ty
                 export :: ABExport GhcTc
export = ABE { abe_ext :: XABE GhcTc
abe_ext  = NoExtField
noExtField
                              , abe_wrap :: HsWrapper
abe_wrap = HsWrapper
idHsWrapper
                              , abe_poly :: IdP GhcTc
abe_poly = Id
sc_top_id
                              , abe_mono :: IdP GhcTc
abe_mono = Id
sc_ev_id
                              , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
noSpecPrags }
                 local_ev_binds :: TcEvBinds
local_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
ev_binds_var
                 bind :: HsBindLR GhcTc GhcTc
bind = AbsBinds { abs_ext :: XAbsBinds GhcTc GhcTc
abs_ext      = NoExtField
noExtField
                                 , abs_tvs :: [Id]
abs_tvs      = [Id]
tyvars
                                 , abs_ev_vars :: [Id]
abs_ev_vars  = [Id]
dfun_evs
                                 , abs_exports :: [ABExport GhcTc]
abs_exports  = [ABExport GhcTc
export]
                                 , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = [TcEvBinds
dfun_ev_binds, TcEvBinds
local_ev_binds]
                                 , abs_binds :: LHsBinds GhcTc
abs_binds    = forall a. Bag a
emptyBag
                                 , abs_sig :: Bool
abs_sig      = Bool
False }
           ; forall (m :: * -> *) a. Monad m => a -> m a
return (Id
sc_top_id, forall l e. l -> e -> GenLocated l e
L (forall ann. SrcSpan -> SrcAnn ann
noAnnSrcSpan SrcSpan
loc) HsBindLR GhcTc GhcTc
bind, Implication
sc_implic) }

-------------------
checkInstConstraints :: TcM result
                     -> TcM (Implication, EvBindsVar, result)
-- See Note [Typechecking plan for instance declarations]
checkInstConstraints :: forall result. TcM result -> TcM (Implication, EvBindsVar, result)
checkInstConstraints TcM result
thing_inside
  = do { (TcLevel
tclvl, WantedConstraints
wanted, result
result) <- forall a. TcM a -> TcM (TcLevel, WantedConstraints, a)
pushLevelAndCaptureConstraints  forall a b. (a -> b) -> a -> b
$
                                    TcM result
thing_inside

       ; EvBindsVar
ev_binds_var <- TcM EvBindsVar
newTcEvBinds
       ; Implication
implic <- TcM Implication
newImplication
       ; let implic' :: Implication
implic' = Implication
implic { ic_tclvl :: TcLevel
ic_tclvl  = TcLevel
tclvl
                              , ic_wanted :: WantedConstraints
ic_wanted = WantedConstraints
wanted
                              , ic_binds :: EvBindsVar
ic_binds  = EvBindsVar
ev_binds_var
                              , ic_info :: SkolemInfo
ic_info   = SkolemInfo
InstSkol }

       ; forall (m :: * -> *) a. Monad m => a -> m a
return (Implication
implic', EvBindsVar
ev_binds_var, result
result) }

{-
Note [Recursive superclasses]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
See #3731, #4809, #5751, #5913, #6117, #6161, which all
describe somewhat more complicated situations, but ones
encountered in practice.

See also tests tcrun020, tcrun021, tcrun033, and #11427.

----- THE PROBLEM --------
The problem is that it is all too easy to create a class whose
superclass is bottom when it should not be.

Consider the following (extreme) situation:
        class C a => D a where ...
        instance D [a] => D [a] where ...   (dfunD)
        instance C [a] => C [a] where ...   (dfunC)
Although this looks wrong (assume D [a] to prove D [a]), it is only a
more extreme case of what happens with recursive dictionaries, and it
can, just about, make sense because the methods do some work before
recursing.

To implement the dfunD we must generate code for the superclass C [a],
which we had better not get by superclass selection from the supplied
argument:
       dfunD :: forall a. D [a] -> D [a]
       dfunD = \d::D [a] -> MkD (scsel d) ..

Otherwise if we later encounter a situation where
we have a [Wanted] dw::D [a] we might solve it thus:
     dw := dfunD dw
Which is all fine except that now ** the superclass C is bottom **!

The instance we want is:
       dfunD :: forall a. D [a] -> D [a]
       dfunD = \d::D [a] -> MkD (dfunC (scsel d)) ...

----- THE SOLUTION --------
The basic solution is simple: be very careful about using superclass
selection to generate a superclass witness in a dictionary function
definition.  More precisely:

  Superclass Invariant: in every class dictionary,
                        every superclass dictionary field
                        is non-bottom

To achieve the Superclass Invariant, in a dfun definition we can
generate a guaranteed-non-bottom superclass witness from:
  (sc1) one of the dictionary arguments itself (all non-bottom)
  (sc2) an immediate superclass of a smaller dictionary
  (sc3) a call of a dfun (always returns a dictionary constructor)

The tricky case is (sc2).  We proceed by induction on the size of
the (type of) the dictionary, defined by GHC.Tc.Validity.sizeTypes.
Let's suppose we are building a dictionary of size 3, and
suppose the Superclass Invariant holds of smaller dictionaries.
Then if we have a smaller dictionary, its immediate superclasses
will be non-bottom by induction.

What does "we have a smaller dictionary" mean?  It might be
one of the arguments of the instance, or one of its superclasses.
Here is an example, taken from CmmExpr:
       class Ord r => UserOfRegs r a where ...
(i1)   instance UserOfRegs r a => UserOfRegs r (Maybe a) where
(i2)   instance (Ord r, UserOfRegs r CmmReg) => UserOfRegs r CmmExpr where

For (i1) we can get the (Ord r) superclass by selection from (UserOfRegs r a),
since it is smaller than the thing we are building (UserOfRegs r (Maybe a).

But for (i2) that isn't the case, so we must add an explicit, and
perhaps surprising, (Ord r) argument to the instance declaration.

Here's another example from #6161:

       class       Super a => Duper a  where ...
       class Duper (Fam a) => Foo a    where ...
(i3)   instance Foo a => Duper (Fam a) where ...
(i4)   instance              Foo Float where ...

It would be horribly wrong to define
   dfDuperFam :: Foo a -> Duper (Fam a)  -- from (i3)
   dfDuperFam d = MkDuper (sc_sel1 (sc_sel2 d)) ...

   dfFooFloat :: Foo Float               -- from (i4)
   dfFooFloat = MkFoo (dfDuperFam dfFooFloat) ...

Now the Super superclass of Duper is definitely bottom!

This won't happen because when processing (i3) we can use the
superclasses of (Foo a), which is smaller, namely Duper (Fam a).  But
that is *not* smaller than the target so we can't take *its*
superclasses.  As a result the program is rightly rejected, unless you
add (Super (Fam a)) to the context of (i3).

Note [Solving superclass constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
How do we ensure that every superclass witness is generated by
one of (sc1) (sc2) or (sc3) in Note [Recursive superclasses].
Answer:

  * Superclass "wanted" constraints have CtOrigin of (ScOrigin size)
    where 'size' is the size of the instance declaration. e.g.
          class C a => D a where...
          instance blah => D [a] where ...
    The wanted superclass constraint for C [a] has origin
    ScOrigin size, where size = size( D [a] ).

  * (sc1) When we rewrite such a wanted constraint, it retains its
    origin.  But if we apply an instance declaration, we can set the
    origin to (ScOrigin infinity), thus lifting any restrictions by
    making prohibitedSuperClassSolve return False.

  * (sc2) ScOrigin wanted constraints can't be solved from a
    superclass selection, except at a smaller type.  This test is
    implemented by GHC.Tc.Solver.Interact.prohibitedSuperClassSolve

  * The "given" constraints of an instance decl have CtOrigin
    GivenOrigin InstSkol.

  * When we make a superclass selection from InstSkol we use
    a CtOrigin of (InstSCOrigin size), where 'size' is the size of
    the constraint whose superclass we are taking.  And similarly
    when taking the superclass of an InstSCOrigin.  This is implemented
    in GHC.Tc.Solver.Canonical.mk_strict_superclasses (in the
    mk_given_loc helper function).

Note [Silent superclass arguments] (historical interest only)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NB1: this note describes our *old* solution to the
     recursive-superclass problem. I'm keeping the Note
     for now, just as institutional memory.
     However, the code for silent superclass arguments
     was removed in late Dec 2014

NB2: the silent-superclass solution introduced new problems
     of its own, in the form of instance overlap.  Tests
     SilentParametersOverlapping, T5051, and T7862 are examples

NB3: the silent-superclass solution also generated tons of
     extra dictionaries.  For example, in monad-transformer
     code, when constructing a Monad dictionary you had to pass
     an Applicative dictionary; and to construct that you need
     a Functor dictionary. Yet these extra dictionaries were
     often never used.  Test T3064 compiled *far* faster after
     silent superclasses were eliminated.

Our solution to this problem "silent superclass arguments".  We pass
to each dfun some ``silent superclass arguments’’, which are the
immediate superclasses of the dictionary we are trying to
construct. In our example:
       dfun :: forall a. C [a] -> D [a] -> D [a]
       dfun = \(dc::C [a]) (dd::D [a]) -> DOrd dc ...
Notice the extra (dc :: C [a]) argument compared to the previous version.

This gives us:

     -----------------------------------------------------------
     DFun Superclass Invariant
     ~~~~~~~~~~~~~~~~~~~~~~~~
     In the body of a DFun, every superclass argument to the
     returned dictionary is
       either   * one of the arguments of the DFun,
       or       * constant, bound at top level
     -----------------------------------------------------------

This net effect is that it is safe to treat a dfun application as
wrapping a dictionary constructor around its arguments (in particular,
a dfun never picks superclasses from the arguments under the
dictionary constructor). No superclass is hidden inside a dfun
application.

The extra arguments required to satisfy the DFun Superclass Invariant
always come first, and are called the "silent" arguments.  You can
find out how many silent arguments there are using Id.dfunNSilent;
and then you can just drop that number of arguments to see the ones
that were in the original instance declaration.

DFun types are built (only) by MkId.mkDictFunId, so that is where we
decide what silent arguments are to be added.
-}

{-
************************************************************************
*                                                                      *
      Type-checking an instance method
*                                                                      *
************************************************************************

tcMethod
- Make the method bindings, as a [(NonRec, HsBinds)], one per method
- Remembering to use fresh Name (the instance method Name) as the binder
- Bring the instance method Ids into scope, for the benefit of tcInstSig
- Use sig_fn mapping instance method Name -> instance tyvars
- Ditto prag_fn
- Use tcValBinds to do the checking
-}

tcMethods :: DFunId -> Class
          -> [TcTyVar] -> [EvVar]
          -> [TcType]
          -> TcEvBinds
          -> ([LTcSpecPrag], TcPragEnv)
          -> [ClassOpItem]
          -> InstBindings GhcRn
          -> TcM ([Id], LHsBinds GhcTc, Bag Implication)
        -- The returned inst_meth_ids all have types starting
        --      forall tvs. theta => ...
tcMethods :: Id
-> Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> ([LTcSpecPrag], TcPragEnv)
-> [ClassOpItem]
-> InstBindings (GhcPass 'Renamed)
-> TcM ([Id], LHsBinds GhcTc, Bag Implication)
tcMethods Id
dfun_id Class
clas [Id]
tyvars [Id]
dfun_ev_vars [PredType]
inst_tys
                  TcEvBinds
dfun_ev_binds ([LTcSpecPrag]
spec_inst_prags, TcPragEnv
prag_fn) [ClassOpItem]
op_items
                  (InstBindings { ib_binds :: forall a. InstBindings a -> LHsBinds a
ib_binds      = LHsBinds (GhcPass 'Renamed)
binds
                                , ib_tyvars :: forall a. InstBindings a -> [Name]
ib_tyvars     = [Name]
lexical_tvs
                                , ib_pragmas :: forall a. InstBindings a -> [LSig a]
ib_pragmas    = [LSig (GhcPass 'Renamed)]
sigs
                                , ib_extensions :: forall a. InstBindings a -> [Extension]
ib_extensions = [Extension]
exts
                                , ib_derived :: forall a. InstBindings a -> Bool
ib_derived    = Bool
is_derived })
  = forall r. [(Name, Id)] -> TcM r -> TcM r
tcExtendNameTyVarEnv ([Name]
lexical_tvs forall a b. [a] -> [b] -> [(a, b)]
`zip` [Id]
tyvars) forall a b. (a -> b) -> a -> b
$
       -- The lexical_tvs scope over the 'where' part
    do { String -> SDoc -> TcRn ()
traceTc String
"tcInstMeth" (forall a. Outputable a => a -> SDoc
ppr [LSig (GhcPass 'Renamed)]
sigs SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr LHsBinds (GhcPass 'Renamed)
binds)
       ; TcRn ()
checkMinimalDefinition
       ; TcRn ()
checkMethBindMembership
       ; ([Id]
ids, [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
binds, [Maybe Implication]
mb_implics) <- forall a. [Extension] -> TcM a -> TcM a
set_exts [Extension]
exts forall a b. (a -> b) -> a -> b
$
                                     forall a. TcM a -> TcM a
unset_warnings_deriving forall a b. (a -> b) -> a -> b
$
                                     forall (m :: * -> *) a b c d.
Monad m =>
(a -> m (b, c, d)) -> [a] -> m ([b], [c], [d])
mapAndUnzip3M ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_item [ClassOpItem]
op_items
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([Id]
ids, forall a. [a] -> Bag a
listToBag [GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc)]
binds, forall a. [a] -> Bag a
listToBag (forall a. [Maybe a] -> [a]
catMaybes [Maybe Implication]
mb_implics)) }
  where
    set_exts :: [LangExt.Extension] -> TcM a -> TcM a
    set_exts :: forall a. [Extension] -> TcM a -> TcM a
set_exts [Extension]
es TcM a
thing = forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
foldr forall gbl lcl a. Extension -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
setXOptM TcM a
thing [Extension]
es

    -- See Note [Avoid -Winaccessible-code when deriving]
    unset_warnings_deriving :: TcM a -> TcM a
    unset_warnings_deriving :: forall a. TcM a -> TcM a
unset_warnings_deriving
      | Bool
is_derived = forall gbl lcl a.
WarningFlag -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
unsetWOptM WarningFlag
Opt_WarnInaccessibleCode
      | Bool
otherwise  = forall a. a -> a
id

    hs_sig_fn :: HsSigFun
hs_sig_fn = [LSig (GhcPass 'Renamed)] -> HsSigFun
mkHsSigFun [LSig (GhcPass 'Renamed)]
sigs
    inst_loc :: SrcSpan
inst_loc  = forall a. NamedThing a => a -> SrcSpan
getSrcSpan Id
dfun_id

    ----------------------
    tc_item :: ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
    tc_item :: ClassOpItem -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_item (Id
sel_id, DefMethInfo
dm_info)
      | Just (LHsBind (GhcPass 'Renamed)
user_bind, SrcSpan
bndr_loc, [LSig (GhcPass 'Renamed)]
prags) <- Name
-> LHsBinds (GhcPass 'Renamed)
-> TcPragEnv
-> Maybe
     (LHsBind (GhcPass 'Renamed), SrcSpan, [LSig (GhcPass 'Renamed)])
findMethodBind (Id -> Name
idName Id
sel_id) LHsBinds (GhcPass 'Renamed)
binds TcPragEnv
prag_fn
      = Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> Bool
-> HsSigFun
-> [LTcSpecPrag]
-> [LSig (GhcPass 'Renamed)]
-> Id
-> LHsBind (GhcPass 'Renamed)
-> SrcSpan
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
tcMethodBody Class
clas [Id]
tyvars [Id]
dfun_ev_vars [PredType]
inst_tys
                              TcEvBinds
dfun_ev_binds Bool
is_derived HsSigFun
hs_sig_fn
                              [LTcSpecPrag]
spec_inst_prags [LSig (GhcPass 'Renamed)]
prags
                              Id
sel_id LHsBind (GhcPass 'Renamed)
user_bind SrcSpan
bndr_loc
      | Bool
otherwise
      = do { String -> SDoc -> TcRn ()
traceTc String
"tc_def" (forall a. Outputable a => a -> SDoc
ppr Id
sel_id)
           ; Id -> DefMethInfo -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_default Id
sel_id DefMethInfo
dm_info }

    ----------------------
    tc_default :: Id -> DefMethInfo
               -> TcM (TcId, LHsBind GhcTc, Maybe Implication)

    tc_default :: Id -> DefMethInfo -> TcM (Id, LHsBind GhcTc, Maybe Implication)
tc_default Id
sel_id (Just (Name
dm_name, DefMethSpec PredType
_))
      = do { (GenLocated
  SrcSpanAnnA (HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed))
meth_bind, [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
inline_prags) <- Id
-> Class
-> Id
-> Name
-> TcM (LHsBind (GhcPass 'Renamed), [LSig (GhcPass 'Renamed)])
mkDefMethBind Id
dfun_id Class
clas Id
sel_id Name
dm_name
           ; Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> Bool
-> HsSigFun
-> [LTcSpecPrag]
-> [LSig (GhcPass 'Renamed)]
-> Id
-> LHsBind (GhcPass 'Renamed)
-> SrcSpan
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
tcMethodBody Class
clas [Id]
tyvars [Id]
dfun_ev_vars [PredType]
inst_tys
                          TcEvBinds
dfun_ev_binds Bool
is_derived HsSigFun
hs_sig_fn
                          [LTcSpecPrag]
spec_inst_prags [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
inline_prags
                          Id
sel_id GenLocated
  SrcSpanAnnA (HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed))
meth_bind SrcSpan
inst_loc }

    tc_default Id
sel_id DefMethInfo
Nothing     -- No default method at all
      = do { String -> SDoc -> TcRn ()
traceTc String
"tc_def: warn" (forall a. Outputable a => a -> SDoc
ppr Id
sel_id)
           ; (Id
meth_id, Id
_) <- Class -> [Id] -> [Id] -> [PredType] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars
                                       [PredType]
inst_tys Id
sel_id
           ; DynFlags
dflags <- forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
           ; let meth_bind :: LHsBind GhcTc
meth_bind = forall (p :: Pass).
IdP (GhcPass p) -> LHsExpr (GhcPass p) -> LHsBind (GhcPass p)
mkVarBind Id
meth_id forall a b. (a -> b) -> a -> b
$
                             HsWrapper -> LHsExpr GhcTc -> LHsExpr GhcTc
mkLHsWrap HsWrapper
lam_wrapper (DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_rhs DynFlags
dflags)
           ; forall (m :: * -> *) a. Monad m => a -> m a
return (Id
meth_id, LHsBind GhcTc
meth_bind, forall a. Maybe a
Nothing) }
      where
        inst_loc' :: SrcSpanAnnA
inst_loc' = forall ann. SrcSpan -> SrcAnn ann
noAnnSrcSpan SrcSpan
inst_loc
        error_rhs :: DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_rhs DynFlags
dflags = forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc'
                                 forall a b. (a -> b) -> a -> b
$ forall p. XApp p -> LHsExpr p -> LHsExpr p -> HsExpr p
HsApp EpAnnCO
noComments GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_fun (DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_msg DynFlags
dflags)
        error_fun :: GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_fun    = forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc' forall a b. (a -> b) -> a -> b
$
                       HsWrapper -> Id -> HsExpr GhcTc
wrapId ([PredType] -> HsWrapper
mkWpTyApps
                                [ HasDebugCallStack => PredType -> PredType
getRuntimeRep PredType
meth_tau, PredType
meth_tau])
                              Id
nO_METHOD_BINDING_ERROR_ID
        error_msg :: DynFlags -> GenLocated SrcSpanAnnA (HsExpr GhcTc)
error_msg DynFlags
dflags = forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
inst_loc'
                                    (forall p. XLitE p -> HsLit p -> HsExpr p
HsLit EpAnnCO
noComments (forall x. XHsStringPrim x -> ByteString -> HsLit x
HsStringPrim SourceText
NoSourceText
                                              (String -> ByteString
unsafeMkByteString (DynFlags -> String
error_string DynFlags
dflags))))
        meth_tau :: PredType
meth_tau     = Id -> [PredType] -> PredType
classMethodInstTy Id
sel_id [PredType]
inst_tys
        error_string :: DynFlags -> String
error_string DynFlags
dflags = DynFlags -> SDoc -> String
showSDoc DynFlags
dflags
                              ([SDoc] -> SDoc
hcat [forall a. Outputable a => a -> SDoc
ppr SrcSpan
inst_loc, SDoc
vbar, forall a. Outputable a => a -> SDoc
ppr Id
sel_id ])
        lam_wrapper :: HsWrapper
lam_wrapper  = [Id] -> HsWrapper
mkWpTyLams [Id]
tyvars HsWrapper -> HsWrapper -> HsWrapper
<.> [Id] -> HsWrapper
mkWpLams [Id]
dfun_ev_vars

    ----------------------
    -- Check if one of the minimal complete definitions is satisfied
    checkMinimalDefinition :: TcRn ()
checkMinimalDefinition
      = forall (m :: * -> *) a. Monad m => Maybe a -> (a -> m ()) -> m ()
whenIsJust (forall a.
Eq a =>
(a -> Bool) -> BooleanFormula a -> Maybe (BooleanFormula a)
isUnsatisfied Name -> Bool
methodExists (Class -> ClassMinimalDef
classMinimalDef Class
clas)) forall a b. (a -> b) -> a -> b
$
        ClassMinimalDef -> TcRn ()
warnUnsatisfiedMinimalDefinition

    methodExists :: Name -> Bool
methodExists Name
meth = forall a. Maybe a -> Bool
isJust (Name
-> LHsBinds (GhcPass 'Renamed)
-> TcPragEnv
-> Maybe
     (LHsBind (GhcPass 'Renamed), SrcSpan, [LSig (GhcPass 'Renamed)])
findMethodBind Name
meth LHsBinds (GhcPass 'Renamed)
binds TcPragEnv
prag_fn)

    ----------------------
    -- Check if any method bindings do not correspond to the class.
    -- See Note [Mismatched class methods and associated type families].
    checkMethBindMembership :: TcRn ()
checkMethBindMembership
      = forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ (SDoc -> TcRn ()
addErrTc forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. Outputable a => a -> Name -> SDoc
badMethodErr Class
clas) [Name]
mismatched_meths
      where
        bind_nms :: [Name]
bind_nms         = forall a b. (a -> b) -> [a] -> [b]
map forall l e. GenLocated l e -> e
unLoc forall a b. (a -> b) -> a -> b
$ forall idL idR. UnXRec idL => LHsBindsLR idL idR -> [LIdP idL]
collectMethodBinders LHsBinds (GhcPass 'Renamed)
binds
        cls_meth_nms :: [Name]
cls_meth_nms     = forall a b. (a -> b) -> [a] -> [b]
map (Id -> Name
idName forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a b. (a, b) -> a
fst) [ClassOpItem]
op_items
        mismatched_meths :: [Name]
mismatched_meths = [Name]
bind_nms forall a. Ord a => [a] -> [a] -> [a]
`minusList` [Name]
cls_meth_nms

{-
Note [Mismatched class methods and associated type families]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's entirely possible for someone to put methods or associated type family
instances inside of a class in which it doesn't belong. For instance, we'd
want to fail if someone wrote this:

  instance Eq () where
    type Rep () = Maybe
    compare = undefined

Since neither the type family `Rep` nor the method `compare` belong to the
class `Eq`. Normally, this is caught in the renamer when resolving RdrNames,
since that would discover that the parent class `Eq` is incorrect.

However, there is a scenario in which the renamer could fail to catch this:
if the instance was generated through Template Haskell, as in #12387. In that
case, Template Haskell will provide fully resolved names (e.g.,
`GHC.Classes.compare`), so the renamer won't notice the sleight-of-hand going
on. For this reason, we also put an extra validity check for this in the
typechecker as a last resort.

Note [Avoid -Winaccessible-code when deriving]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Winaccessible-code can be particularly noisy when deriving instances for
GADTs. Consider the following example (adapted from #8128):

  data T a where
    MkT1 :: Int -> T Int
    MkT2 :: T Bool
    MkT3 :: T Bool
  deriving instance Eq (T a)
  deriving instance Ord (T a)

In the derived Ord instance, GHC will generate the following code:

  instance Ord (T a) where
    compare x y
      = case x of
          MkT2
            -> case y of
                 MkT1 {} -> GT
                 MkT2    -> EQ
                 _       -> LT
          ...

However, that MkT1 is unreachable, since the type indices for MkT1 and MkT2
differ, so if -Winaccessible-code is enabled, then deriving this instance will
result in unwelcome warnings.

One conceivable approach to fixing this issue would be to change `deriving Ord`
such that it becomes smarter about not generating unreachable cases. This,
however, would be a highly nontrivial refactor, as we'd have to propagate
through typing information everywhere in the algorithm that generates Ord
instances in order to determine which cases were unreachable. This seems like
a lot of work for minimal gain, so we have opted not to go for this approach.

Instead, we take the much simpler approach of always disabling
-Winaccessible-code for derived code. To accomplish this, we do the following:

1. In tcMethods (which typechecks method bindings), disable
   -Winaccessible-code.
2. When creating Implications during typechecking, record this flag
   (in ic_warn_inaccessible) at the time of creation.
3. After typechecking comes error reporting, where GHC must decide how to
   report inaccessible code to the user, on an Implication-by-Implication
   basis. If an Implication's DynFlags indicate that -Winaccessible-code was
   disabled, then don't bother reporting it. That's it!
-}

------------------------
tcMethodBody :: Class -> [TcTyVar] -> [EvVar] -> [TcType]
             -> TcEvBinds -> Bool
             -> HsSigFun
             -> [LTcSpecPrag] -> [LSig GhcRn]
             -> Id -> LHsBind GhcRn -> SrcSpan
             -> TcM (TcId, LHsBind GhcTc, Maybe Implication)
tcMethodBody :: Class
-> [Id]
-> [Id]
-> [PredType]
-> TcEvBinds
-> Bool
-> HsSigFun
-> [LTcSpecPrag]
-> [LSig (GhcPass 'Renamed)]
-> Id
-> LHsBind (GhcPass 'Renamed)
-> SrcSpan
-> TcM (Id, LHsBind GhcTc, Maybe Implication)
tcMethodBody Class
clas [Id]
tyvars [Id]
dfun_ev_vars [PredType]
inst_tys
                     TcEvBinds
dfun_ev_binds Bool
is_derived
                     HsSigFun
sig_fn [LTcSpecPrag]
spec_inst_prags [LSig (GhcPass 'Renamed)]
prags
                     Id
sel_id (L SrcSpanAnnA
bind_loc HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed)
meth_bind) SrcSpan
bndr_loc
  = TcM
  (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
   Maybe Implication)
-> TcM
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
      Maybe Implication)
add_meth_ctxt forall a b. (a -> b) -> a -> b
$
    do { String -> SDoc -> TcRn ()
traceTc String
"tcMethodBody" (forall a. Outputable a => a -> SDoc
ppr Id
sel_id SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr (Id -> PredType
idType Id
sel_id) SDoc -> SDoc -> SDoc
$$ forall a. Outputable a => a -> SDoc
ppr SrcSpan
bndr_loc)
       ; (Id
global_meth_id, Id
local_meth_id) <- forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan SrcSpan
bndr_loc forall a b. (a -> b) -> a -> b
$
                                            Class -> [Id] -> [Id] -> [PredType] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars
                                                      [PredType]
inst_tys Id
sel_id

       ; let lm_bind :: HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed)
lm_bind = HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed)
meth_bind { fun_id :: LIdP (GhcPass 'Renamed)
fun_id = forall l e. l -> e -> GenLocated l e
L (forall ann. SrcSpan -> SrcAnn ann
noAnnSrcSpan SrcSpan
bndr_loc)
                                                        (Id -> Name
idName Id
local_meth_id) }
                       -- Substitute the local_meth_name for the binder
                       -- NB: the binding is always a FunBind

            -- taking instance signature into account might change the type of
            -- the local_meth_id
       ; (Implication
meth_implic, EvBindsVar
ev_binds_var, Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind)
             <- forall result. TcM result -> TcM (Implication, EvBindsVar, result)
checkInstConstraints forall a b. (a -> b) -> a -> b
$
                HsSigFun
-> Id -> Id -> LHsBind (GhcPass 'Renamed) -> TcM (LHsBinds GhcTc)
tcMethodBodyHelp HsSigFun
sig_fn Id
sel_id Id
local_meth_id (forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
bind_loc HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed)
lm_bind)

       ; Id
global_meth_id <- Id -> [LSig (GhcPass 'Renamed)] -> TcM Id
addInlinePrags Id
global_meth_id [LSig (GhcPass 'Renamed)]
prags
       ; [LTcSpecPrag]
spec_prags     <- Id -> [LSig (GhcPass 'Renamed)] -> TcM [LTcSpecPrag]
tcSpecPrags Id
global_meth_id [LSig (GhcPass 'Renamed)]
prags

        ; let specs :: TcSpecPrags
specs  = Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
mk_meth_spec_prags Id
global_meth_id [LTcSpecPrag]
spec_inst_prags [LTcSpecPrag]
spec_prags
              export :: ABExport GhcTc
export = ABE { abe_ext :: XABE GhcTc
abe_ext   = NoExtField
noExtField
                           , abe_poly :: IdP GhcTc
abe_poly  = Id
global_meth_id
                           , abe_mono :: IdP GhcTc
abe_mono  = Id
local_meth_id
                           , abe_wrap :: HsWrapper
abe_wrap  = HsWrapper
idHsWrapper
                           , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
specs }

              local_ev_binds :: TcEvBinds
local_ev_binds = EvBindsVar -> TcEvBinds
TcEvBinds EvBindsVar
ev_binds_var
              full_bind :: HsBindLR GhcTc GhcTc
full_bind = AbsBinds { abs_ext :: XAbsBinds GhcTc GhcTc
abs_ext      = NoExtField
noExtField
                                   , abs_tvs :: [Id]
abs_tvs      = [Id]
tyvars
                                   , abs_ev_vars :: [Id]
abs_ev_vars  = [Id]
dfun_ev_vars
                                   , abs_exports :: [ABExport GhcTc]
abs_exports  = [ABExport GhcTc
export]
                                   , abs_ev_binds :: [TcEvBinds]
abs_ev_binds = [TcEvBinds
dfun_ev_binds, TcEvBinds
local_ev_binds]
                                   , abs_binds :: LHsBinds GhcTc
abs_binds    = Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind
                                   , abs_sig :: Bool
abs_sig      = Bool
True }

        ; forall (m :: * -> *) a. Monad m => a -> m a
return (Id
global_meth_id, forall l e. l -> e -> GenLocated l e
L SrcSpanAnnA
bind_loc HsBindLR GhcTc GhcTc
full_bind, forall a. a -> Maybe a
Just Implication
meth_implic) }
  where
        -- For instance decls that come from deriving clauses
        -- we want to print out the full source code if there's an error
        -- because otherwise the user won't see the code at all
    add_meth_ctxt :: TcM
  (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
   Maybe Implication)
-> TcM
     (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
      Maybe Implication)
add_meth_ctxt TcM
  (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
   Maybe Implication)
thing
      | Bool
is_derived = forall a. SDoc -> TcM a -> TcM a
addLandmarkErrCtxt (Id -> Class -> [PredType] -> SDoc
derivBindCtxt Id
sel_id Class
clas [PredType]
inst_tys) TcM
  (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
   Maybe Implication)
thing
      | Bool
otherwise  = TcM
  (Id, GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc),
   Maybe Implication)
thing

tcMethodBodyHelp :: HsSigFun -> Id -> TcId
                 -> LHsBind GhcRn -> TcM (LHsBinds GhcTc)
tcMethodBodyHelp :: HsSigFun
-> Id -> Id -> LHsBind (GhcPass 'Renamed) -> TcM (LHsBinds GhcTc)
tcMethodBodyHelp HsSigFun
hs_sig_fn Id
sel_id Id
local_meth_id LHsBind (GhcPass 'Renamed)
meth_bind
  | Just LHsSigType (GhcPass 'Renamed)
hs_sig_ty <- HsSigFun
hs_sig_fn Name
sel_name
              -- There is a signature in the instance
              -- See Note [Instance method signatures]
  = do { (PredType
sig_ty, HsWrapper
hs_wrap)
             <- forall a. SrcSpan -> TcRn a -> TcRn a
setSrcSpan (forall a e. GenLocated (SrcSpanAnn' a) e -> SrcSpan
getLocA LHsSigType (GhcPass 'Renamed)
hs_sig_ty) forall a b. (a -> b) -> a -> b
$
                do { Bool
inst_sigs <- forall gbl lcl. Extension -> TcRnIf gbl lcl Bool
xoptM Extension
LangExt.InstanceSigs
                   ; Bool -> SDoc -> TcRn ()
checkTc Bool
inst_sigs (Name -> LHsSigType (GhcPass 'Renamed) -> SDoc
misplacedInstSig Name
sel_name LHsSigType (GhcPass 'Renamed)
hs_sig_ty)
                   ; PredType
sig_ty  <- UserTypeCtxt -> LHsSigType (GhcPass 'Renamed) -> TcM PredType
tcHsSigType (Name -> Bool -> UserTypeCtxt
FunSigCtxt Name
sel_name Bool
False) LHsSigType (GhcPass 'Renamed)
hs_sig_ty
                   ; let local_meth_ty :: PredType
local_meth_ty = Id -> PredType
idType Id
local_meth_id
                         ctxt :: UserTypeCtxt
ctxt = Name -> Bool -> UserTypeCtxt
FunSigCtxt Name
sel_name Bool
False
                                -- False <=> do not report redundant constraints when
                                --           checking instance-sig <= class-meth-sig
                                -- The instance-sig is the focus here; the class-meth-sig
                                -- is fixed (#18036)
                   ; let orig :: CtOrigin
orig = Name -> PredType -> PredType -> CtOrigin
InstanceSigOrigin Name
sel_name PredType
sig_ty PredType
local_meth_ty
                   ; HsWrapper
hs_wrap <- forall a. (TidyEnv -> TcM (TidyEnv, SDoc)) -> TcM a -> TcM a
addErrCtxtM (Name -> PredType -> PredType -> TidyEnv -> TcM (TidyEnv, SDoc)
methSigCtxt Name
sel_name PredType
sig_ty PredType
local_meth_ty) forall a b. (a -> b) -> a -> b
$
                                CtOrigin -> UserTypeCtxt -> PredType -> PredType -> TcM HsWrapper
tcSubTypeSigma CtOrigin
orig UserTypeCtxt
ctxt PredType
sig_ty PredType
local_meth_ty
                   ; forall (m :: * -> *) a. Monad m => a -> m a
return (PredType
sig_ty, HsWrapper
hs_wrap) }

       ; Name
inner_meth_name <- OccName -> TcM Name
newName (Name -> OccName
nameOccName Name
sel_name)
       ; let ctxt :: UserTypeCtxt
ctxt = Name -> Bool -> UserTypeCtxt
FunSigCtxt Name
sel_name Bool
True
                    -- True <=> check for redundant constraints in the
                    --          user-specified instance signature
             inner_meth_id :: Id
inner_meth_id  = HasDebugCallStack => Name -> PredType -> PredType -> Id
mkLocalId Name
inner_meth_name PredType
Many PredType
sig_ty
             inner_meth_sig :: TcIdSigInfo
inner_meth_sig = CompleteSig { sig_bndr :: Id
sig_bndr = Id
inner_meth_id
                                          , sig_ctxt :: UserTypeCtxt
sig_ctxt = UserTypeCtxt
ctxt
                                          , sig_loc :: SrcSpan
sig_loc  = forall a e. GenLocated (SrcSpanAnn' a) e -> SrcSpan
getLocA LHsSigType (GhcPass 'Renamed)
hs_sig_ty }


       ; (Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind, [Id
inner_id]) <- TcPragEnv
-> TcIdSigInfo
-> LHsBind (GhcPass 'Renamed)
-> TcM (LHsBinds GhcTc, [Id])
tcPolyCheck NameEnv [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
no_prag_fn TcIdSigInfo
inner_meth_sig LHsBind (GhcPass 'Renamed)
meth_bind

       ; let export :: ABExport GhcTc
export = ABE { abe_ext :: XABE GhcTc
abe_ext   = NoExtField
noExtField
                          , abe_poly :: IdP GhcTc
abe_poly  = Id
local_meth_id
                          , abe_mono :: IdP GhcTc
abe_mono  = Id
inner_id
                          , abe_wrap :: HsWrapper
abe_wrap  = HsWrapper
hs_wrap
                          , abe_prags :: TcSpecPrags
abe_prags = TcSpecPrags
noSpecPrags }

       ; forall (m :: * -> *) a. Monad m => a -> m a
return (forall a. a -> Bag a
unitBag forall a b. (a -> b) -> a -> b
$ forall l e. l -> e -> GenLocated l e
L (forall l e. GenLocated l e -> l
getLoc LHsBind (GhcPass 'Renamed)
meth_bind) forall a b. (a -> b) -> a -> b
$
                 AbsBinds { abs_ext :: XAbsBinds GhcTc GhcTc
abs_ext = NoExtField
noExtField, abs_tvs :: [Id]
abs_tvs = [], abs_ev_vars :: [Id]
abs_ev_vars = []
                          , abs_exports :: [ABExport GhcTc]
abs_exports = [ABExport GhcTc
export]
                          , abs_binds :: LHsBinds GhcTc
abs_binds = Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind, abs_ev_binds :: [TcEvBinds]
abs_ev_binds = []
                          , abs_sig :: Bool
abs_sig = Bool
True }) }

  | Bool
otherwise  -- No instance signature
  = do { let ctxt :: UserTypeCtxt
ctxt = Name -> Bool -> UserTypeCtxt
FunSigCtxt Name
sel_name Bool
False
                    -- False <=> don't report redundant constraints
                    -- The signature is not under the users control!
             tc_sig :: TcIdSigInfo
tc_sig = UserTypeCtxt -> Id -> TcIdSigInfo
completeSigFromId UserTypeCtxt
ctxt Id
local_meth_id
              -- Absent a type sig, there are no new scoped type variables here
              -- Only the ones from the instance decl itself, which are already
              -- in scope.  Example:
              --      class C a where { op :: forall b. Eq b => ... }
              --      instance C [c] where { op = <rhs> }
              -- In <rhs>, 'c' is scope but 'b' is not!

       ; (Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind, [Id]
_) <- TcPragEnv
-> TcIdSigInfo
-> LHsBind (GhcPass 'Renamed)
-> TcM (LHsBinds GhcTc, [Id])
tcPolyCheck NameEnv [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
no_prag_fn TcIdSigInfo
tc_sig LHsBind (GhcPass 'Renamed)
meth_bind
       ; forall (m :: * -> *) a. Monad m => a -> m a
return Bag (GenLocated SrcSpanAnnA (HsBindLR GhcTc GhcTc))
tc_bind }

  where
    sel_name :: Name
sel_name   = Id -> Name
idName Id
sel_id
    no_prag_fn :: TcPragEnv
no_prag_fn = TcPragEnv
emptyPragEnv   -- No pragmas for local_meth_id;
                                -- they are all for meth_id


------------------------
mkMethIds :: Class -> [TcTyVar] -> [EvVar]
          -> [TcType] -> Id -> TcM (TcId, TcId)
             -- returns (poly_id, local_id), but ignoring any instance signature
             -- See Note [Instance method signatures]
mkMethIds :: Class -> [Id] -> [Id] -> [PredType] -> Id -> TcM (Id, Id)
mkMethIds Class
clas [Id]
tyvars [Id]
dfun_ev_vars [PredType]
inst_tys Id
sel_id
  = do  { Name
poly_meth_name  <- OccName -> TcM Name
newName (OccName -> OccName
mkClassOpAuxOcc OccName
sel_occ)
        ; Name
local_meth_name <- OccName -> TcM Name
newName OccName
sel_occ
                  -- Base the local_meth_name on the selector name, because
                  -- type errors from tcMethodBody come from here
        ; let poly_meth_id :: Id
poly_meth_id  = HasDebugCallStack => Name -> PredType -> PredType -> Id
mkLocalId Name
poly_meth_name  PredType
Many PredType
poly_meth_ty
              local_meth_id :: Id
local_meth_id = HasDebugCallStack => Name -> PredType -> PredType -> Id
mkLocalId Name
local_meth_name PredType
Many PredType
local_meth_ty

        ; forall (m :: * -> *) a. Monad m => a -> m a
return (Id
poly_meth_id, Id
local_meth_id) }
  where
    sel_name :: Name
sel_name      = Id -> Name
idName Id
sel_id
    sel_occ :: OccName
sel_occ       = Name -> OccName
nameOccName Name
sel_name
    local_meth_ty :: PredType
local_meth_ty = Class -> Id -> [PredType] -> PredType
instantiateMethod Class
clas Id
sel_id [PredType]
inst_tys
    poly_meth_ty :: PredType
poly_meth_ty  = [Id] -> [PredType] -> PredType -> PredType
mkSpecSigmaTy [Id]
tyvars [PredType]
theta PredType
local_meth_ty
    theta :: [PredType]
theta         = forall a b. (a -> b) -> [a] -> [b]
map Id -> PredType
idType [Id]
dfun_ev_vars

methSigCtxt :: Name -> TcType -> TcType -> TidyEnv -> TcM (TidyEnv, SDoc)
methSigCtxt :: Name -> PredType -> PredType -> TidyEnv -> TcM (TidyEnv, SDoc)
methSigCtxt Name
sel_name PredType
sig_ty PredType
meth_ty TidyEnv
env0
  = do { (TidyEnv
env1, PredType
sig_ty)  <- TidyEnv -> PredType -> TcM (TidyEnv, PredType)
zonkTidyTcType TidyEnv
env0 PredType
sig_ty
       ; (TidyEnv
env2, PredType
meth_ty) <- TidyEnv -> PredType -> TcM (TidyEnv, PredType)
zonkTidyTcType TidyEnv
env1 PredType
meth_ty
       ; let msg :: SDoc
msg = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"When checking that instance signature for" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr Name
sel_name))
                      Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"is more general than its signature in the class"
                              , String -> SDoc
text String
"Instance sig:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr PredType
sig_ty
                              , String -> SDoc
text String
"   Class sig:" SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr PredType
meth_ty ])
       ; forall (m :: * -> *) a. Monad m => a -> m a
return (TidyEnv
env2, SDoc
msg) }

misplacedInstSig :: Name -> LHsSigType GhcRn -> SDoc
misplacedInstSig :: Name -> LHsSigType (GhcPass 'Renamed) -> SDoc
misplacedInstSig Name
name LHsSigType (GhcPass 'Renamed)
hs_ty
  = [SDoc] -> SDoc
vcat [ SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"Illegal type signature in instance declaration:")
              Int
2 (SDoc -> Int -> SDoc -> SDoc
hang (forall a. NamedThing a => a -> SDoc
pprPrefixName Name
name)
                    Int
2 (SDoc
dcolon SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr LHsSigType (GhcPass 'Renamed)
hs_ty))
         , String -> SDoc
text String
"(Use InstanceSigs to allow this)" ]

{- Note [Instance method signatures]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With -XInstanceSigs we allow the user to supply a signature for the
method in an instance declaration.  Here is an artificial example:

       data T a = MkT a
       instance Ord a => Ord (T a) where
         (>) :: forall b. b -> b -> Bool
         (>) = error "You can't compare Ts"

The instance signature can be *more* polymorphic than the instantiated
class method (in this case: Age -> Age -> Bool), but it cannot be less
polymorphic.  Moreover, if a signature is given, the implementation
code should match the signature, and type variables bound in the
singature should scope over the method body.

We achieve this by building a TcSigInfo for the method, whether or not
there is an instance method signature, and using that to typecheck
the declaration (in tcMethodBody).  That means, conveniently,
that the type variables bound in the signature will scope over the body.

What about the check that the instance method signature is more
polymorphic than the instantiated class method type?  We just do a
tcSubType call in tcMethodBodyHelp, and generate a nested AbsBind, like
this (for the example above

 AbsBind { abs_tvs = [a], abs_ev_vars = [d:Ord a]
         , abs_exports
             = ABExport { (>) :: forall a. Ord a => T a -> T a -> Bool
                        , gr_lcl :: T a -> T a -> Bool }
         , abs_binds
             = AbsBind { abs_tvs = [], abs_ev_vars = []
                       , abs_exports = ABExport { gr_lcl :: T a -> T a -> Bool
                                                , gr_inner :: forall b. b -> b -> Bool }
                       , abs_binds = AbsBind { abs_tvs = [b], abs_ev_vars = []
                                             , ..etc.. }
               } }

Wow!  Three nested AbsBinds!
 * The outer one abstracts over the tyvars and dicts for the instance
 * The middle one is only present if there is an instance signature,
   and does the impedance matching for that signature
 * The inner one is for the method binding itself against either the
   signature from the class, or the instance signature.
-}

----------------------
mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
        -- Adapt the 'SPECIALISE instance' pragmas to work for this method Id
        -- There are two sources:
        --   * spec_prags_for_me: {-# SPECIALISE op :: <blah> #-}
        --   * spec_prags_from_inst: derived from {-# SPECIALISE instance :: <blah> #-}
        --     These ones have the dfun inside, but [perhaps surprisingly]
        --     the correct wrapper.
        -- See Note [Handling SPECIALISE pragmas] in GHC.Tc.Gen.Bind
mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> [LTcSpecPrag] -> TcSpecPrags
mk_meth_spec_prags Id
meth_id [LTcSpecPrag]
spec_inst_prags [LTcSpecPrag]
spec_prags_for_me
  = [LTcSpecPrag] -> TcSpecPrags
SpecPrags ([LTcSpecPrag]
spec_prags_for_me forall a. [a] -> [a] -> [a]
++ [LTcSpecPrag]
spec_prags_from_inst)
  where
    spec_prags_from_inst :: [LTcSpecPrag]
spec_prags_from_inst
       | InlinePragma -> Bool
isInlinePragma (Id -> InlinePragma
idInlinePragma Id
meth_id)
       = []  -- Do not inherit SPECIALISE from the instance if the
             -- method is marked INLINE, because then it'll be inlined
             -- and the specialisation would do nothing. (Indeed it'll provoke
             -- a warning from the desugarer
       | Bool
otherwise
       = [ forall l e. l -> e -> GenLocated l e
L SrcSpan
inst_loc (Id -> HsWrapper -> InlinePragma -> TcSpecPrag
SpecPrag Id
meth_id HsWrapper
wrap InlinePragma
inl)
         | L SrcSpan
inst_loc (SpecPrag Id
_       HsWrapper
wrap InlinePragma
inl) <- [LTcSpecPrag]
spec_inst_prags]


mkDefMethBind :: DFunId -> Class -> Id -> Name
              -> TcM (LHsBind GhcRn, [LSig GhcRn])
-- The is a default method (vanailla or generic) defined in the class
-- So make a binding   op = $dmop @t1 @t2
-- where $dmop is the name of the default method in the class,
-- and t1,t2 are the instance types.
-- See Note [Default methods in instances] for why we use
-- visible type application here
mkDefMethBind :: Id
-> Class
-> Id
-> Name
-> TcM (LHsBind (GhcPass 'Renamed), [LSig (GhcPass 'Renamed)])
mkDefMethBind Id
dfun_id Class
clas Id
sel_id Name
dm_name
  = do  { DynFlags
dflags <- forall (m :: * -> *). HasDynFlags m => m DynFlags
getDynFlags
        ; Logger
logger <- forall (m :: * -> *). HasLogger m => m Logger
getLogger
        ; Id
dm_id <- Name -> TcM Id
tcLookupId Name
dm_name
        ; let inline_prag :: InlinePragma
inline_prag = Id -> InlinePragma
idInlinePragma Id
dm_id
              inline_prags :: [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
inline_prags | InlinePragma -> Bool
isAnyInlinePragma InlinePragma
inline_prag
                           = [forall a an. a -> LocatedAn an a
noLocA (forall pass.
XInlineSig pass -> LIdP pass -> InlinePragma -> Sig pass
InlineSig forall a. EpAnn a
noAnn GenLocated SrcSpanAnnN Name
fn InlinePragma
inline_prag)]
                           | Bool
otherwise
                           = []
                 -- Copy the inline pragma (if any) from the default method
                 -- to this version. Note [INLINE and default methods]

              fn :: GenLocated SrcSpanAnnN Name
fn   = forall a an. a -> LocatedAn an a
noLocA (Id -> Name
idName Id
sel_id)
              visible_inst_tys :: [PredType]
visible_inst_tys = [ PredType
ty | (TyConBinder
tcb, PredType
ty) <- TyCon -> [TyConBinder]
tyConBinders (Class -> TyCon
classTyCon Class
clas) forall a b. [a] -> [b] -> [(a, b)]
`zip` [PredType]
inst_tys
                                      , TyConBinder -> ArgFlag
tyConBinderArgFlag TyConBinder
tcb forall a. Eq a => a -> a -> Bool
/= ArgFlag
Inferred ]
              rhs :: LocatedA (HsExpr (GhcPass 'Renamed))
rhs  = forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl' LHsExpr (GhcPass 'Renamed)
-> PredType -> LHsExpr (GhcPass 'Renamed)
mk_vta (forall (p :: Pass) a.
IsSrcSpanAnn p a =>
IdP (GhcPass p) -> LHsExpr (GhcPass p)
nlHsVar Name
dm_name) [PredType]
visible_inst_tys
              bind :: GenLocated
  SrcSpanAnnA (HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed))
bind = forall a an. a -> LocatedAn an a
noLocA forall a b. (a -> b) -> a -> b
$ Origin
-> GenLocated SrcSpanAnnN Name
-> [LMatch (GhcPass 'Renamed) (LHsExpr (GhcPass 'Renamed))]
-> HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed)
mkTopFunBind Origin
Generated GenLocated SrcSpanAnnN Name
fn forall a b. (a -> b) -> a -> b
$
                             [forall (p :: Pass) (body :: * -> *).
(Anno (Match (GhcPass p) (LocatedA (body (GhcPass p))))
 ~ SrcSpanAnnA,
 Anno (GRHS (GhcPass p) (LocatedA (body (GhcPass p)))) ~ SrcSpan) =>
HsMatchContext (NoGhcTc (GhcPass p))
-> [LPat (GhcPass p)]
-> LocatedA (body (GhcPass p))
-> LMatch (GhcPass p) (LocatedA (body (GhcPass p)))
mkSimpleMatch (forall p. LIdP p -> HsMatchContext p
mkPrefixFunRhs GenLocated SrcSpanAnnN Name
fn) [] LocatedA (HsExpr (GhcPass 'Renamed))
rhs]

        ; forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO (Logger
-> DynFlags -> DumpFlag -> String -> DumpFormat -> SDoc -> IO ()
dumpIfSet_dyn Logger
logger DynFlags
dflags DumpFlag
Opt_D_dump_deriv String
"Filling in method body"
                   DumpFormat
FormatHaskell
                   ([SDoc] -> SDoc
vcat [forall a. Outputable a => a -> SDoc
ppr Class
clas SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr [PredType]
inst_tys,
                          Int -> SDoc -> SDoc
nest Int
2 (forall a. Outputable a => a -> SDoc
ppr Id
sel_id SDoc -> SDoc -> SDoc
<+> SDoc
equals SDoc -> SDoc -> SDoc
<+> forall a. Outputable a => a -> SDoc
ppr LocatedA (HsExpr (GhcPass 'Renamed))
rhs)]))

       ; forall (m :: * -> *) a. Monad m => a -> m a
return (GenLocated
  SrcSpanAnnA (HsBindLR (GhcPass 'Renamed) (GhcPass 'Renamed))
bind, [GenLocated SrcSpanAnnA (Sig (GhcPass 'Renamed))]
inline_prags) }
  where
    ([Id]
_, [PredType]
_, Class
_, [PredType]
inst_tys) = PredType -> ([Id], [PredType], Class, [PredType])
tcSplitDFunTy (Id -> PredType
idType Id
dfun_id)

    mk_vta :: LHsExpr GhcRn -> Type -> LHsExpr GhcRn
    mk_vta :: LHsExpr (GhcPass 'Renamed)
-> PredType -> LHsExpr (GhcPass 'Renamed)
mk_vta LHsExpr (GhcPass 'Renamed)
fun PredType
ty = forall a an. a -> LocatedAn an a
noLocA (forall p.
XAppTypeE p -> LHsExpr p -> LHsWcType (NoGhcTc p) -> HsExpr p
HsAppType NoExtField
noExtField LHsExpr (GhcPass 'Renamed)
fun (forall thing. thing -> HsWildCardBndrs (GhcPass 'Renamed) thing
mkEmptyWildCardBndrs forall a b. (a -> b) -> a -> b
$ forall (p :: Pass). LHsType (GhcPass p) -> LHsType (GhcPass p)
nlHsParTy
                                                forall a b. (a -> b) -> a -> b
$ forall a an. a -> LocatedAn an a
noLocA forall a b. (a -> b) -> a -> b
$ forall pass. XXType pass -> HsType pass
XHsType PredType
ty))
       -- NB: use visible type application
       -- See Note [Default methods in instances]

----------------------
derivBindCtxt :: Id -> Class -> [Type ] -> SDoc
derivBindCtxt :: Id -> Class -> [PredType] -> SDoc
derivBindCtxt Id
sel_id Class
clas [PredType]
tys
   = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"When typechecking the code for" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr Id
sel_id)
          , Int -> SDoc -> SDoc
nest Int
2 (String -> SDoc
text String
"in a derived instance for"
                    SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (Class -> [PredType] -> SDoc
pprClassPred Class
clas [PredType]
tys) SDoc -> SDoc -> SDoc
<> SDoc
colon)
          , Int -> SDoc -> SDoc
nest Int
2 forall a b. (a -> b) -> a -> b
$ String -> SDoc
text String
"To see the code I am typechecking, use -ddump-deriv" ]

warnUnsatisfiedMinimalDefinition :: ClassMinimalDef -> TcM ()
warnUnsatisfiedMinimalDefinition :: ClassMinimalDef -> TcRn ()
warnUnsatisfiedMinimalDefinition ClassMinimalDef
mindef
  = do { Bool
warn <- forall gbl lcl. WarningFlag -> TcRnIf gbl lcl Bool
woptM WarningFlag
Opt_WarnMissingMethods
       ; WarnReason -> Bool -> SDoc -> TcRn ()
warnTc (WarningFlag -> WarnReason
Reason WarningFlag
Opt_WarnMissingMethods) Bool
warn SDoc
message
       }
  where
    message :: SDoc
message = [SDoc] -> SDoc
vcat [String -> SDoc
text String
"No explicit implementation for"
                   ,Int -> SDoc -> SDoc
nest Int
2 forall a b. (a -> b) -> a -> b
$ forall a. Outputable a => BooleanFormula a -> SDoc
pprBooleanFormulaNice ClassMinimalDef
mindef
                   ]

{-
Note [Export helper functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We arrange to export the "helper functions" of an instance declaration,
so that they are not subject to preInlineUnconditionally, even if their
RHS is trivial.  Reason: they are mentioned in the DFunUnfolding of
the dict fun as Ids, not as CoreExprs, so we can't substitute a
non-variable for them.

We could change this by making DFunUnfoldings have CoreExprs, but it
seems a bit simpler this way.

Note [Default methods in instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this

   class Baz v x where
      foo :: x -> x
      foo y = <blah>

   instance Baz Int Int

From the class decl we get

   $dmfoo :: forall v x. Baz v x => x -> x
   $dmfoo y = <blah>

Notice that the type is ambiguous.  So we use Visible Type Application
to disambiguate:

   $dBazIntInt = MkBaz fooIntInt
   fooIntInt = $dmfoo @Int @Int

Lacking VTA we'd get ambiguity errors involving the default method.  This applies
equally to vanilla default methods (#1061) and generic default methods
(#12220).

Historical note: before we had VTA we had to generate
post-type-checked code, which took a lot more code, and didn't work for
generic default methods.

Note [INLINE and default methods]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Default methods need special case.  They are supposed to behave rather like
macros.  For example

  class Foo a where
    op1, op2 :: Bool -> a -> a

    {-# INLINE op1 #-}
    op1 b x = op2 (not b) x

  instance Foo Int where
    -- op1 via default method
    op2 b x = <blah>

The instance declaration should behave

   just as if 'op1' had been defined with the
   code, and INLINE pragma, from its original
   definition.

That is, just as if you'd written

  instance Foo Int where
    op2 b x = <blah>

    {-# INLINE op1 #-}
    op1 b x = op2 (not b) x

So for the above example we generate:

  {-# INLINE $dmop1 #-}
  -- $dmop1 has an InlineCompulsory unfolding
  $dmop1 d b x = op2 d (not b) x

  $fFooInt = MkD $cop1 $cop2

  {-# INLINE $cop1 #-}
  $cop1 = $dmop1 $fFooInt

  $cop2 = <blah>

Note carefully:

* We *copy* any INLINE pragma from the default method $dmop1 to the
  instance $cop1.  Otherwise we'll just inline the former in the
  latter and stop, which isn't what the user expected

* Regardless of its pragma, we give the default method an
  unfolding with an InlineCompulsory source. That means
  that it'll be inlined at every use site, notably in
  each instance declaration, such as $cop1.  This inlining
  must happen even though
    a) $dmop1 is not saturated in $cop1
    b) $cop1 itself has an INLINE pragma

  It's vital that $dmop1 *is* inlined in this way, to allow the mutual
  recursion between $fooInt and $cop1 to be broken

* To communicate the need for an InlineCompulsory to the desugarer
  (which makes the Unfoldings), we use the IsDefaultMethod constructor
  in TcSpecPrags.


************************************************************************
*                                                                      *
        Specialise instance pragmas
*                                                                      *
************************************************************************

Note [SPECIALISE instance pragmas]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider

   instance (Ix a, Ix b) => Ix (a,b) where
     {-# SPECIALISE instance Ix (Int,Int) #-}
     range (x,y) = ...

We make a specialised version of the dictionary function, AND
specialised versions of each *method*.  Thus we should generate
something like this:

  $dfIxPair :: (Ix a, Ix b) => Ix (a,b)
  {-# DFUN [$crangePair, ...] #-}
  {-# SPECIALISE $dfIxPair :: Ix (Int,Int) #-}
  $dfIxPair da db = Ix ($crangePair da db) (...other methods...)

  $crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)]
  {-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-}
  $crange da db = <blah>

The SPECIALISE pragmas are acted upon by the desugarer, which generate

  dii :: Ix Int
  dii = ...

  $s$dfIxPair :: Ix ((Int,Int),(Int,Int))
  {-# DFUN [$crangePair di di, ...] #-}
  $s$dfIxPair = Ix ($crangePair di di) (...)

  {-# RULE forall (d1,d2:Ix Int). $dfIxPair Int Int d1 d2 = $s$dfIxPair #-}

  $s$crangePair :: ((Int,Int),(Int,Int)) -> [(Int,Int)]
  $c$crangePair = ...specialised RHS of $crangePair...

  {-# RULE forall (d1,d2:Ix Int). $crangePair Int Int d1 d2 = $s$crangePair #-}

Note that

  * The specialised dictionary $s$dfIxPair is very much needed, in case we
    call a function that takes a dictionary, but in a context where the
    specialised dictionary can be used.  See #7797.

  * The ClassOp rule for 'range' works equally well on $s$dfIxPair, because
    it still has a DFunUnfolding.  See Note [ClassOp/DFun selection]

  * A call (range ($dfIxPair Int Int d1 d2)) might simplify two ways:
       --> {ClassOp rule for range}     $crangePair Int Int d1 d2
       --> {SPEC rule for $crangePair}  $s$crangePair
    or thus:
       --> {SPEC rule for $dfIxPair}    range $s$dfIxPair
       --> {ClassOpRule for range}      $s$crangePair
    It doesn't matter which way.

  * We want to specialise the RHS of both $dfIxPair and $crangePair,
    but the SAME HsWrapper will do for both!  We can call tcSpecPrag
    just once, and pass the result (in spec_inst_info) to tcMethods.
-}

tcSpecInstPrags :: DFunId -> InstBindings GhcRn
                -> TcM ([LTcSpecPrag], TcPragEnv)
tcSpecInstPrags :: Id
-> InstBindings (GhcPass 'Renamed)
-> TcM ([LTcSpecPrag], TcPragEnv)
tcSpecInstPrags Id
dfun_id (InstBindings { ib_binds :: forall a. InstBindings a -> LHsBinds a
ib_binds = LHsBinds (GhcPass 'Renamed)
binds, ib_pragmas :: forall a. InstBindings a -> [LSig a]
ib_pragmas = [LSig (GhcPass 'Renamed)]
uprags })
  = do { [LTcSpecPrag]
spec_inst_prags <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (forall a b an. (a -> TcM b) -> LocatedAn an a -> TcM (Located b)
wrapLocAM (Id -> Sig (GhcPass 'Renamed) -> TcM TcSpecPrag
tcSpecInst Id
dfun_id)) forall a b. (a -> b) -> a -> b
$
                            forall a. (a -> Bool) -> [a] -> [a]
filter forall p. UnXRec p => LSig p -> Bool
isSpecInstLSig [LSig (GhcPass 'Renamed)]
uprags
             -- The filter removes the pragmas for methods
       ; forall (m :: * -> *) a. Monad m => a -> m a
return ([LTcSpecPrag]
spec_inst_prags, [LSig (GhcPass 'Renamed)]
-> LHsBinds (GhcPass 'Renamed) -> TcPragEnv
mkPragEnv [LSig (GhcPass 'Renamed)]
uprags LHsBinds (GhcPass 'Renamed)
binds) }

------------------------------
tcSpecInst :: Id -> Sig GhcRn -> TcM TcSpecPrag
tcSpecInst :: Id -> Sig (GhcPass 'Renamed) -> TcM TcSpecPrag
tcSpecInst Id
dfun_id prag :: Sig (GhcPass 'Renamed)
prag@(SpecInstSig XSpecInstSig (GhcPass 'Renamed)
_ SourceText
_ LHsSigType (GhcPass 'Renamed)
hs_ty)
  = forall a. SDoc -> TcM a -> TcM a
addErrCtxt (forall a. Outputable a => a -> SDoc
spec_ctxt Sig (GhcPass 'Renamed)
prag) forall a b. (a -> b) -> a -> b
$
    do  { PredType
spec_dfun_ty <- UserTypeCtxt -> LHsSigType (GhcPass 'Renamed) -> TcM PredType
tcHsClsInstType UserTypeCtxt
SpecInstCtxt LHsSigType (GhcPass 'Renamed)
hs_ty
        ; HsWrapper
co_fn <- UserTypeCtxt -> PredType -> PredType -> TcM HsWrapper
tcSpecWrapper UserTypeCtxt
SpecInstCtxt (Id -> PredType
idType Id
dfun_id) PredType
spec_dfun_ty
        ; forall (m :: * -> *) a. Monad m => a -> m a
return (Id -> HsWrapper -> InlinePragma -> TcSpecPrag
SpecPrag Id
dfun_id HsWrapper
co_fn InlinePragma
defaultInlinePragma) }
  where
    spec_ctxt :: a -> SDoc
spec_ctxt a
prag = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"In the pragma:") Int
2 (forall a. Outputable a => a -> SDoc
ppr a
prag)

tcSpecInst Id
_  Sig (GhcPass 'Renamed)
_ = forall a. String -> a
panic String
"tcSpecInst"

{-
************************************************************************
*                                                                      *
\subsection{Error messages}
*                                                                      *
************************************************************************
-}

instDeclCtxt1 :: LHsSigType GhcRn -> SDoc
instDeclCtxt1 :: LHsSigType (GhcPass 'Renamed) -> SDoc
instDeclCtxt1 LHsSigType (GhcPass 'Renamed)
hs_inst_ty
  = SDoc -> SDoc
inst_decl_ctxt (forall a. Outputable a => a -> SDoc
ppr (forall (p :: Pass). LHsSigType (GhcPass p) -> LHsType (GhcPass p)
getLHsInstDeclHead LHsSigType (GhcPass 'Renamed)
hs_inst_ty))

instDeclCtxt2 :: Type -> SDoc
instDeclCtxt2 :: PredType -> SDoc
instDeclCtxt2 PredType
dfun_ty
  = SDoc -> SDoc
inst_decl_ctxt (forall a. Outputable a => a -> SDoc
ppr (Class -> [PredType] -> PredType
mkClassPred Class
cls [PredType]
tys))
  where
    ([Id]
_,[PredType]
_,Class
cls,[PredType]
tys) = PredType -> ([Id], [PredType], Class, [PredType])
tcSplitDFunTy PredType
dfun_ty

inst_decl_ctxt :: SDoc -> SDoc
inst_decl_ctxt :: SDoc -> SDoc
inst_decl_ctxt SDoc
doc = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"In the instance declaration for")
                        Int
2 (SDoc -> SDoc
quotes SDoc
doc)

badBootFamInstDeclErr :: SDoc
badBootFamInstDeclErr :: SDoc
badBootFamInstDeclErr
  = String -> SDoc
text String
"Illegal family instance in hs-boot file"

notFamily :: TyCon -> SDoc
notFamily :: TyCon -> SDoc
notFamily TyCon
tycon
  = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"Illegal family instance for" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr TyCon
tycon)
         , Int -> SDoc -> SDoc
nest Int
2 forall a b. (a -> b) -> a -> b
$ SDoc -> SDoc
parens (forall a. Outputable a => a -> SDoc
ppr TyCon
tycon SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"is not an indexed type family")]

assocInClassErr :: TyCon -> SDoc
assocInClassErr :: TyCon -> SDoc
assocInClassErr TyCon
name
 = String -> SDoc
text String
"Associated type" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr TyCon
name) SDoc -> SDoc -> SDoc
<+>
   String -> SDoc
text String
"must be inside a class instance"

badFamInstDecl :: TyCon -> SDoc
badFamInstDecl :: TyCon -> SDoc
badFamInstDecl TyCon
tc_name
  = [SDoc] -> SDoc
vcat [ String -> SDoc
text String
"Illegal family instance for" SDoc -> SDoc -> SDoc
<+>
           SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr TyCon
tc_name)
         , Int -> SDoc -> SDoc
nest Int
2 (SDoc -> SDoc
parens forall a b. (a -> b) -> a -> b
$ String -> SDoc
text String
"Use TypeFamilies to allow indexed type families") ]

notOpenFamily :: TyCon -> SDoc
notOpenFamily :: TyCon -> SDoc
notOpenFamily TyCon
tc
  = String -> SDoc
text String
"Illegal instance for closed family" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (forall a. Outputable a => a -> SDoc
ppr TyCon
tc)