{- Author: George Karachalias Pattern Matching Coverage Checking. -} {-# LANGUAGE CPP #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE TupleSections #-} {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE MultiWayIf #-} {-# LANGUAGE LambdaCase #-} module GHC.HsToCore.PmCheck ( -- Checking and printing checkSingle, checkMatches, checkGuardMatches, needToRunPmCheck, isMatchContextPmChecked, -- See Note [Type and Term Equality Propagation] addTyCsDs, addScrutTmCs, addPatTmCs ) where #include "HsVersions.h" import GhcPrelude import GHC.HsToCore.PmCheck.Types import GHC.HsToCore.PmCheck.Oracle import GHC.HsToCore.PmCheck.Ppr import BasicTypes (Origin, isGenerated) import CoreSyn (CoreExpr, Expr(Var,App)) import FastString (unpackFS, lengthFS) import DynFlags import GHC.Hs import TcHsSyn import Id import ConLike import Name import FamInst import TysWiredIn import SrcLoc import Util import Outputable import DataCon import TyCon import Var (EvVar) import Coercion import TcEvidence import {-# SOURCE #-} DsExpr (dsExpr, dsLExpr, dsSyntaxExpr) import {-# SOURCE #-} DsBinds (dsHsWrapper) import DsUtils (selectMatchVar) import MatchLit (dsLit, dsOverLit) import DsMonad import Bag import TyCoRep import Type import DsUtils (isTrueLHsExpr) import Maybes import qualified GHC.LanguageExtensions as LangExt import Control.Monad (when, forM_, zipWithM) import Data.List (elemIndex) import qualified Data.Semigroup as Semi {- This module checks pattern matches for: \begin{enumerate} \item Equations that are redundant \item Equations with inaccessible right-hand-side \item Exhaustiveness \end{enumerate} The algorithm is based on the paper: "GADTs Meet Their Match: Pattern-matching Warnings That Account for GADTs, Guards, and Laziness" http://people.cs.kuleuven.be/~george.karachalias/papers/p424-karachalias.pdf %************************************************************************ %* * Pattern Match Check Types %* * %************************************************************************ -} -- | A very simple language for pattern guards. Let bindings, bang patterns, -- and matching variables against flat constructor patterns. data PmGrd = -- | @PmCon x K tvs dicts args@ corresponds to a -- @K tvs dicts args <- x@ guard. The @tvs@ and @args@ are bound in this -- construct, the @x@ is just a use. -- For the arguments' meaning see 'GHC.Hs.Pat.ConPatOut'. PmCon { pm_id :: !Id, pm_con_con :: !PmAltCon, pm_con_tvs :: ![TyVar], pm_con_dicts :: ![EvVar], pm_con_args :: ![Id] } -- | @PmBang x@ corresponds to a @seq x True@ guard. | PmBang { pm_id :: !Id } -- | @PmLet x expr@ corresponds to a @let x = expr@ guard. This actually -- /binds/ @x@. | PmLet { pm_id :: !Id, pm_let_expr :: !CoreExpr } -- | Should not be user-facing. instance Outputable PmGrd where ppr (PmCon x alt _con_tvs _con_dicts con_args) = hsep [ppr alt, hsep (map ppr con_args), text "<-", ppr x] ppr (PmBang x) = char '!' <> ppr x ppr (PmLet x expr) = hsep [text "let", ppr x, text "=", ppr expr] type GrdVec = [PmGrd] -- | Each 'Delta' is proof (i.e., a model of the fact) that some values are not -- covered by a pattern match. E.g. @f Nothing = @ might be given an -- uncovered set @[x :-> Just y]@ or @[x /= Nothing]@, where @x@ is the variable -- matching against @f@'s first argument. type Uncovered = [Delta] -- Instead of keeping the whole sets in memory, we keep a boolean for both the -- covered and the divergent set (we store the uncovered set though, since we -- want to print it). For both the covered and the divergent we have: -- -- True <=> The set is non-empty -- -- hence: -- C = True ==> Useful clause (no warning) -- C = False, D = True ==> Clause with inaccessible RHS -- C = False, D = False ==> Redundant clause data Covered = Covered | NotCovered deriving Show instance Outputable Covered where ppr = text . show -- Like the or monoid for booleans -- Covered = True, Uncovered = False instance Semi.Semigroup Covered where Covered <> _ = Covered _ <> Covered = Covered NotCovered <> NotCovered = NotCovered instance Monoid Covered where mempty = NotCovered mappend = (Semi.<>) data Diverged = Diverged | NotDiverged deriving Show instance Outputable Diverged where ppr = text . show instance Semi.Semigroup Diverged where Diverged <> _ = Diverged _ <> Diverged = Diverged NotDiverged <> NotDiverged = NotDiverged instance Monoid Diverged where mempty = NotDiverged mappend = (Semi.<>) data Precision = Approximate | Precise deriving (Eq, Show) instance Outputable Precision where ppr = text . show instance Semi.Semigroup Precision where Approximate <> _ = Approximate _ <> Approximate = Approximate Precise <> Precise = Precise instance Monoid Precision where mempty = Precise mappend = (Semi.<>) -- | A triple of covered, uncovered, and divergent sets. -- -- Also stores a flag 'presultApprox' denoting whether we ran into the -- 'maxPmCheckModels' limit for the purpose of hints in warning messages to -- maybe increase the limit. data PartialResult = PartialResult { presultCovered :: Covered , presultUncovered :: Uncovered , presultDivergent :: Diverged , presultApprox :: Precision } emptyPartialResult :: PartialResult emptyPartialResult = PartialResult { presultUncovered = mempty , presultCovered = mempty , presultDivergent = mempty , presultApprox = mempty } combinePartialResults :: PartialResult -> PartialResult -> PartialResult combinePartialResults (PartialResult cs1 vsa1 ds1 ap1) (PartialResult cs2 vsa2 ds2 ap2) = PartialResult (cs1 Semi.<> cs2) (vsa1 Semi.<> vsa2) (ds1 Semi.<> ds2) (ap1 Semi.<> ap2) -- the result is approximate if either is instance Outputable PartialResult where ppr (PartialResult c unc d pc) = hang (text "PartialResult" <+> ppr c <+> ppr d <+> ppr pc) 2 (ppr_unc unc) where ppr_unc = braces . fsep . punctuate comma . map ppr instance Semi.Semigroup PartialResult where (<>) = combinePartialResults instance Monoid PartialResult where mempty = emptyPartialResult mappend = (Semi.<>) -- | Pattern check result -- -- * Redundant clauses -- * Not-covered clauses (or their type, if no pattern is available) -- * Clauses with inaccessible RHS -- * A flag saying whether we ran into the 'maxPmCheckModels' limit for the -- purpose of suggesting to crank it up in the warning message -- -- More details about the classification of clauses into useful, redundant -- and with inaccessible right hand side can be found here: -- -- https://gitlab.haskell.org/ghc/ghc/wikis/pattern-match-check -- data PmResult = PmResult { pmresultRedundant :: [Located [LPat GhcTc]] , pmresultUncovered :: [Delta] , pmresultInaccessible :: [Located [LPat GhcTc]] , pmresultApproximate :: Precision } instance Outputable PmResult where ppr pmr = hang (text "PmResult") 2 $ vcat [ text "pmresultRedundant" <+> ppr (pmresultRedundant pmr) , text "pmresultUncovered" <+> ppr (pmresultUncovered pmr) , text "pmresultInaccessible" <+> ppr (pmresultInaccessible pmr) , text "pmresultApproximate" <+> ppr (pmresultApproximate pmr) ] {- %************************************************************************ %* * Entry points to the checker: checkSingle and checkMatches %* * %************************************************************************ -} -- | Check a single pattern binding (let) checkSingle :: DynFlags -> DsMatchContext -> Id -> Pat GhcTc -> DsM () checkSingle dflags ctxt@(DsMatchContext _ locn) var p = do tracePm "checkSingle" (vcat [ppr ctxt, ppr var, ppr p]) res <- checkSingle' locn var p dsPmWarn dflags ctxt [var] res -- | Check a single pattern binding (let) checkSingle' :: SrcSpan -> Id -> Pat GhcTc -> DsM PmResult checkSingle' locn var p = do fam_insts <- dsGetFamInstEnvs grds <- translatePat fam_insts var p missing <- getPmDelta tracePm "checkSingle': missing" (ppr missing) PartialResult cs us ds pc <- pmCheck grds [] 1 missing dflags <- getDynFlags us' <- getNFirstUncovered [var] (maxUncoveredPatterns dflags + 1) us let plain = PmResult { pmresultRedundant = [] , pmresultUncovered = us' , pmresultInaccessible = [] , pmresultApproximate = pc } return $ case (cs,ds) of (Covered , _ ) -> plain -- useful (NotCovered, NotDiverged) -> plain { pmresultRedundant = m } -- redundant (NotCovered, Diverged ) -> plain { pmresultInaccessible = m } -- inaccessible rhs where m = [cL locn [cL locn p]] -- | Exhaustive for guard matches, is used for guards in pattern bindings and -- in @MultiIf@ expressions. checkGuardMatches :: HsMatchContext Name -- Match context -> GRHSs GhcTc (LHsExpr GhcTc) -- Guarded RHSs -> DsM () checkGuardMatches hs_ctx guards@(GRHSs _ grhss _) = do dflags <- getDynFlags let combinedLoc = foldl1 combineSrcSpans (map getLoc grhss) dsMatchContext = DsMatchContext hs_ctx combinedLoc match = cL combinedLoc $ Match { m_ext = noExtField , m_ctxt = hs_ctx , m_pats = [] , m_grhss = guards } checkMatches dflags dsMatchContext [] [match] checkGuardMatches _ (XGRHSs nec) = noExtCon nec -- | Check a matchgroup (case, functions, etc.) checkMatches :: DynFlags -> DsMatchContext -> [Id] -> [LMatch GhcTc (LHsExpr GhcTc)] -> DsM () checkMatches dflags ctxt vars matches = do tracePm "checkMatches" (hang (vcat [ppr ctxt , ppr vars , text "Matches:"]) 2 (vcat (map ppr matches))) res <- checkMatches' vars matches dsPmWarn dflags ctxt vars res -- | Check a matchgroup (case, functions, etc.). checkMatches' :: [Id] -> [LMatch GhcTc (LHsExpr GhcTc)] -> DsM PmResult checkMatches' vars matches = do init_delta <- getPmDelta missing <- case matches of -- This must be an -XEmptyCase. See Note [Checking EmptyCase] [] | [var] <- vars -> maybeToList <$> addTmCt init_delta (TmVarNonVoid var) _ -> pure [init_delta] tracePm "checkMatches': missing" (ppr missing) (rs,us,ds,pc) <- go matches missing dflags <- getDynFlags us' <- getNFirstUncovered vars (maxUncoveredPatterns dflags + 1) us return $ PmResult { pmresultRedundant = map hsLMatchToLPats rs , pmresultUncovered = us' , pmresultInaccessible = map hsLMatchToLPats ds , pmresultApproximate = pc } where go :: [LMatch GhcTc (LHsExpr GhcTc)] -> Uncovered -> DsM ( [LMatch GhcTc (LHsExpr GhcTc)] , Uncovered , [LMatch GhcTc (LHsExpr GhcTc)] , Precision) go [] missing = return ([], missing, [], Precise) go (m:ms) missing = do tracePm "checkMatches': go" (ppr m) dflags <- getDynFlags fam_insts <- dsGetFamInstEnvs (clause, guards) <- translateMatch fam_insts vars m let limit = maxPmCheckModels dflags n_siblings = length missing throttled_check delta = snd <$> throttle limit (pmCheck clause guards) n_siblings delta r@(PartialResult cs missing' ds pc1) <- runMany throttled_check missing tracePm "checkMatches': go: res" (ppr r) (rs, final_u, is, pc2) <- go ms missing' return $ case (cs, ds) of -- useful (Covered, _ ) -> (rs, final_u, is, pc1 Semi.<> pc2) -- redundant (NotCovered, NotDiverged) -> (m:rs, final_u, is, pc1 Semi.<> pc2) -- inaccessible (NotCovered, Diverged ) -> (rs, final_u, m:is, pc1 Semi.<> pc2) hsLMatchToLPats :: LMatch id body -> Located [LPat id] hsLMatchToLPats (dL->L l (Match { m_pats = pats })) = cL l pats hsLMatchToLPats _ = panic "checkMatches'" getNFirstUncovered :: [Id] -> Int -> [Delta] -> DsM [Delta] getNFirstUncovered _ 0 _ = pure [] getNFirstUncovered _ _ [] = pure [] getNFirstUncovered vars n (delta:deltas) = do front <- provideEvidence vars n delta back <- getNFirstUncovered vars (n - length front) deltas pure (front ++ back) {- Note [Checking EmptyCase] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -XEmptyCase is useful for matching on empty data types like 'Void'. For example, the following is a complete match: f :: Void -> () f x = case x of {} Really, -XEmptyCase is the only way to write a program that at the same time is safe (@f _ = error "boom"@ is not because of ⊥), doesn't trigger a warning (@f !_ = error "inaccessible" has inaccessible RHS) and doesn't turn an exception into divergence (@f x = f x@). Semantically, unlike every other case expression, -XEmptyCase is strict in its match var x, which rules out ⊥ as an inhabitant. So we add x /~ ⊥ to the initial Delta and check if there are any values left to match on. -} {- %************************************************************************ %* * Transform source syntax to *our* syntax %* * %************************************************************************ -} -- ----------------------------------------------------------------------- -- * Utilities -- | Smart constructor that eliminates trivial lets mkPmLetVar :: Id -> Id -> GrdVec mkPmLetVar x y | x == y = [] mkPmLetVar x y = [PmLet x (Var y)] -- | ADT constructor pattern => no existentials, no local constraints vanillaConGrd :: Id -> DataCon -> [Id] -> PmGrd vanillaConGrd scrut con arg_ids = PmCon { pm_id = scrut, pm_con_con = PmAltConLike (RealDataCon con) , pm_con_tvs = [], pm_con_dicts = [], pm_con_args = arg_ids } -- | Creates a 'GrdVec' refining a match var of list type to a list, -- where list fields are matched against the incoming tagged 'GrdVec's. -- For example: -- @mkListGrds "a" "[(x, True <- x),(y, !y)]"@ -- to -- @"[(x:b) <- a, True <- x, (y:c) <- b, seq y True, [] <- c]"@ -- where b,c are freshly allocated in @mkListGrds@ and a is the match variable. mkListGrds :: Id -> [(Id, GrdVec)] -> DsM GrdVec -- See Note [Order of guards matter] for why we need to intertwine guards -- on list elements. mkListGrds a [] = pure [vanillaConGrd a nilDataCon []] mkListGrds a ((x, head_grds):xs) = do b <- mkPmId (idType a) tail_grds <- mkListGrds b xs pure $ vanillaConGrd a consDataCon [x, b] : head_grds ++ tail_grds -- | Create a 'GrdVec' refining a match variable to a 'PmLit'. mkPmLitGrds :: Id -> PmLit -> DsM GrdVec mkPmLitGrds x (PmLit _ (PmLitString s)) = do -- We translate String literals to list literals for better overlap reasoning. -- It's a little unfortunate we do this here rather than in -- 'GHC.HsToCore.PmCheck.Oracle.trySolve' and 'GHC.HsToCore.PmCheck.Oracle.addRefutableAltCon', but it's so much -- simpler here. -- See Note [Representation of Strings in TmState] in GHC.HsToCore.PmCheck.Oracle vars <- traverse mkPmId (take (lengthFS s) (repeat charTy)) let mk_char_lit y c = mkPmLitGrds y (PmLit charTy (PmLitChar c)) char_grdss <- zipWithM mk_char_lit vars (unpackFS s) mkListGrds x (zip vars char_grdss) mkPmLitGrds x lit = do let grd = PmCon { pm_id = x , pm_con_con = PmAltLit lit , pm_con_tvs = [] , pm_con_dicts = [] , pm_con_args = [] } pure [grd] -- ----------------------------------------------------------------------- -- * Transform (Pat Id) into GrdVec -- | @translatePat _ x pat@ transforms @pat@ into a 'GrdVec', where -- the variable representing the match is @x@. translatePat :: FamInstEnvs -> Id -> Pat GhcTc -> DsM GrdVec translatePat fam_insts x pat = case pat of WildPat _ty -> pure [] VarPat _ y -> pure (mkPmLetVar (unLoc y) x) ParPat _ p -> translateLPat fam_insts x p LazyPat _ _ -> pure [] -- like a wildcard BangPat _ p -> -- Add the bang in front of the list, because it will happen before any -- nested stuff. (PmBang x :) <$> translateLPat fam_insts x p -- (x@pat) ==> Translate pat with x as match var and handle impedance -- mismatch with incoming match var AsPat _ (dL->L _ y) p -> (mkPmLetVar y x ++) <$> translateLPat fam_insts y p SigPat _ p _ty -> translateLPat fam_insts x p -- See Note [Translate CoPats] -- Generally the translation is -- pat |> co ===> let y = x |> co, pat <- y where y is a match var of pat CoPat _ wrapper p _ty | isIdHsWrapper wrapper -> translatePat fam_insts x p | WpCast co <- wrapper, isReflexiveCo co -> translatePat fam_insts x p | otherwise -> do (y, grds) <- translatePatV fam_insts p wrap_rhs_y <- dsHsWrapper wrapper pure (PmLet y (wrap_rhs_y (Var x)) : grds) -- (n + k) ===> let b = x >= k, True <- b, let n = x-k NPlusKPat _pat_ty (dL->L _ n) k1 k2 ge minus -> do b <- mkPmId boolTy let grd_b = vanillaConGrd b trueDataCon [] [ke1, ke2] <- traverse dsOverLit [unLoc k1, k2] rhs_b <- dsSyntaxExpr ge [Var x, ke1] rhs_n <- dsSyntaxExpr minus [Var x, ke2] pure [PmLet b rhs_b, grd_b, PmLet n rhs_n] -- (fun -> pat) ===> let y = fun x, pat <- y where y is a match var of pat ViewPat _arg_ty lexpr pat -> do (y, grds) <- translateLPatV fam_insts pat fun <- dsLExpr lexpr pure $ PmLet y (App fun (Var x)) : grds -- list ListPat (ListPatTc _elem_ty Nothing) ps -> translateListPat fam_insts x ps -- overloaded list ListPat (ListPatTc elem_ty (Just (pat_ty, to_list))) pats -> do dflags <- getDynFlags case splitListTyConApp_maybe pat_ty of Just _e_ty | not (xopt LangExt.RebindableSyntax dflags) -- Just translate it as a regular ListPat -> translateListPat fam_insts x pats _ -> do y <- mkPmId (mkListTy elem_ty) grds <- translateListPat fam_insts y pats rhs_y <- dsSyntaxExpr to_list [Var x] pure $ PmLet y rhs_y : grds -- (a) In the presence of RebindableSyntax, we don't know anything about -- `toList`, we should treat `ListPat` as any other view pattern. -- -- (b) In the absence of RebindableSyntax, -- - If the pat_ty is `[a]`, then we treat the overloaded list pattern -- as ordinary list pattern. Although we can give an instance -- `IsList [Int]` (more specific than the default `IsList [a]`), in -- practice, we almost never do that. We assume the `to_list` is -- the `toList` from `instance IsList [a]`. -- -- - Otherwise, we treat the `ListPat` as ordinary view pattern. -- -- See #14547, especially comment#9 and comment#10. ConPatOut { pat_con = (dL->L _ con) , pat_arg_tys = arg_tys , pat_tvs = ex_tvs , pat_dicts = dicts , pat_args = ps } -> do translateConPatOut fam_insts x con arg_tys ex_tvs dicts ps NPat ty (dL->L _ olit) mb_neg _ -> do -- See Note [Literal short cut] in MatchLit.hs -- We inline the Literal short cut for @ty@ here, because @ty@ is more -- precise than the field of OverLitTc, which is all that dsOverLit (which -- normally does the literal short cut) can look at. Also @ty@ matches the -- type of the scrutinee, so info on both pattern and scrutinee (for which -- short cutting in dsOverLit works properly) is overloaded iff either is. dflags <- getDynFlags core_expr <- case olit of OverLit{ ol_val = val, ol_ext = OverLitTc rebindable _ } | not rebindable , Just expr <- shortCutLit dflags val ty -> dsExpr expr _ -> dsOverLit olit let lit = expectJust "failed to detect OverLit" (coreExprAsPmLit core_expr) let lit' = case mb_neg of Just _ -> expectJust "failed to negate lit" (negatePmLit lit) Nothing -> lit mkPmLitGrds x lit' LitPat _ lit -> do core_expr <- dsLit (convertLit lit) let lit = expectJust "failed to detect Lit" (coreExprAsPmLit core_expr) mkPmLitGrds x lit TuplePat _tys pats boxity -> do (vars, grdss) <- mapAndUnzipM (translateLPatV fam_insts) pats let tuple_con = tupleDataCon boxity (length vars) pure $ vanillaConGrd x tuple_con vars : concat grdss SumPat _ty p alt arity -> do (y, grds) <- translateLPatV fam_insts p let sum_con = sumDataCon alt arity -- See Note [Unboxed tuple RuntimeRep vars] in TyCon pure $ vanillaConGrd x sum_con [y] : grds -- -------------------------------------------------------------------------- -- Not supposed to happen ConPatIn {} -> panic "Check.translatePat: ConPatIn" SplicePat {} -> panic "Check.translatePat: SplicePat" XPat n -> noExtCon n -- | 'translatePat', but also select and return a new match var. translatePatV :: FamInstEnvs -> Pat GhcTc -> DsM (Id, GrdVec) translatePatV fam_insts pat = do x <- selectMatchVar pat grds <- translatePat fam_insts x pat pure (x, grds) translateLPat :: FamInstEnvs -> Id -> LPat GhcTc -> DsM GrdVec translateLPat fam_insts x = translatePat fam_insts x . unLoc -- | 'translateLPat', but also select and return a new match var. translateLPatV :: FamInstEnvs -> LPat GhcTc -> DsM (Id, GrdVec) translateLPatV fam_insts = translatePatV fam_insts . unLoc -- | @translateListPat _ x [p1, ..., pn]@ is basically -- @translateConPatOut _ x $(mkListConPatOuts [p1, ..., pn]>@ without ever -- constructing the 'ConPatOut's. translateListPat :: FamInstEnvs -> Id -> [LPat GhcTc] -> DsM GrdVec translateListPat fam_insts x pats = do vars_and_grdss <- traverse (translateLPatV fam_insts) pats mkListGrds x vars_and_grdss -- | Translate a constructor pattern translateConPatOut :: FamInstEnvs -> Id -> ConLike -> [Type] -> [TyVar] -> [EvVar] -> HsConPatDetails GhcTc -> DsM GrdVec translateConPatOut fam_insts x con univ_tys ex_tvs dicts = \case PrefixCon ps -> go_field_pats (zip [0..] ps) InfixCon p1 p2 -> go_field_pats (zip [0..] [p1,p2]) RecCon (HsRecFields fs _) -> go_field_pats (rec_field_ps fs) where -- The actual argument types (instantiated) arg_tys = conLikeInstOrigArgTys con (univ_tys ++ mkTyVarTys ex_tvs) -- Extract record field patterns tagged by field index from a list of -- LHsRecField rec_field_ps fs = map (tagged_pat . unLoc) fs where tagged_pat f = (lbl_to_index (getName (hsRecFieldId f)), hsRecFieldArg f) -- Unfortunately the label info is empty when the DataCon wasn't defined -- with record field labels, hence we translate to field index. orig_lbls = map flSelector $ conLikeFieldLabels con lbl_to_index lbl = expectJust "lbl_to_index" $ elemIndex lbl orig_lbls go_field_pats tagged_pats = do -- The fields that appear might not be in the correct order. So first -- do a PmCon match, then force according to field strictness and then -- force evaluation of the field patterns in the order given by -- the first field of @tagged_pats@. -- See Note [Field match order for RecCon] -- Translate the mentioned field patterns. We're doing this first to get -- the Ids for pm_con_args. let trans_pat (n, pat) = do (var, pvec) <- translateLPatV fam_insts pat pure ((n, var), pvec) (tagged_vars, arg_grdss) <- mapAndUnzipM trans_pat tagged_pats let get_pat_id n ty = case lookup n tagged_vars of Just var -> pure var Nothing -> mkPmId ty -- 1. the constructor pattern match itself arg_ids <- zipWithM get_pat_id [0..] arg_tys let con_grd = PmCon x (PmAltConLike con) ex_tvs dicts arg_ids -- 2. bang strict fields let arg_is_banged = map isBanged $ conLikeImplBangs con bang_grds = map PmBang $ filterByList arg_is_banged arg_ids -- 3. guards from field selector patterns let arg_grds = concat arg_grdss -- tracePm "ConPatOut" (ppr x $$ ppr con $$ ppr arg_ids) -- -- Store the guards in exactly that order -- 1. 2. 3. pure (con_grd : bang_grds ++ arg_grds) -- Translate a single match translateMatch :: FamInstEnvs -> [Id] -> LMatch GhcTc (LHsExpr GhcTc) -> DsM (GrdVec, [GrdVec]) translateMatch fam_insts vars (dL->L _ (Match { m_pats = pats, m_grhss = grhss })) = do pats' <- concat <$> zipWithM (translateLPat fam_insts) vars pats guards' <- mapM (translateGuards fam_insts) guards -- tracePm "translateMatch" (vcat [ppr pats, ppr pats', ppr guards, ppr guards']) return (pats', guards') where extractGuards :: LGRHS GhcTc (LHsExpr GhcTc) -> [GuardStmt GhcTc] extractGuards (dL->L _ (GRHS _ gs _)) = map unLoc gs extractGuards _ = panic "translateMatch" guards = map extractGuards (grhssGRHSs grhss) translateMatch _ _ _ = panic "translateMatch" -- ----------------------------------------------------------------------- -- * Transform source guards (GuardStmt Id) to simpler PmGrds -- | Translate a list of guard statements to a 'GrdVec' translateGuards :: FamInstEnvs -> [GuardStmt GhcTc] -> DsM GrdVec translateGuards fam_insts guards = concat <$> mapM (translateGuard fam_insts) guards -- | Translate a guard statement to a 'GrdVec' translateGuard :: FamInstEnvs -> GuardStmt GhcTc -> DsM GrdVec translateGuard fam_insts guard = case guard of BodyStmt _ e _ _ -> translateBoolGuard e LetStmt _ binds -> translateLet (unLoc binds) BindStmt _ p e _ _ -> translateBind fam_insts p e LastStmt {} -> panic "translateGuard LastStmt" ParStmt {} -> panic "translateGuard ParStmt" TransStmt {} -> panic "translateGuard TransStmt" RecStmt {} -> panic "translateGuard RecStmt" ApplicativeStmt {} -> panic "translateGuard ApplicativeLastStmt" XStmtLR nec -> noExtCon nec -- | Translate let-bindings translateLet :: HsLocalBinds GhcTc -> DsM GrdVec translateLet _binds = return [] -- | Translate a pattern guard -- @pat <- e ==> let x = e; @ translateBind :: FamInstEnvs -> LPat GhcTc -> LHsExpr GhcTc -> DsM GrdVec translateBind fam_insts p e = dsLExpr e >>= \case Var y | Nothing <- isDataConId_maybe y -- RHS is a variable, so that will allow us to omit the let -> translateLPat fam_insts y p rhs -> do (x, grds) <- translateLPatV fam_insts p pure (PmLet x rhs : grds) -- | Translate a boolean guard -- @e ==> let x = e; True <- x@ translateBoolGuard :: LHsExpr GhcTc -> DsM GrdVec translateBoolGuard e | isJust (isTrueLHsExpr e) = return [] -- The formal thing to do would be to generate (True <- True) -- but it is trivial to solve so instead we give back an empty -- GrdVec for efficiency | otherwise = dsLExpr e >>= \case Var y | Nothing <- isDataConId_maybe y -- Omit the let by matching on y -> pure [vanillaConGrd y trueDataCon []] rhs -> do x <- mkPmId boolTy pure $ [PmLet x rhs, vanillaConGrd x trueDataCon []] {- Note [Field match order for RecCon] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The order for RecCon field patterns actually determines evaluation order of the pattern match. For example: data T = T { a :: !Bool, b :: Char, c :: Int } f :: T -> () f T{ c = 42, b = 'b' } = () Then * @f (T (error "a") (error "b") (error "c"))@ errors out with "a" because of the strict field. * @f (T True (error "b") (error "c"))@ errors out with "c" because it is mentioned frist in the pattern match. This means we can't just desugar the pattern match to the PatVec @[T !_ 'b' 42]@. Instead we have to generate variable matches that have strictness according to the field declarations and afterwards force them in the right order. As a result, we get the PatVec @[T !_ b c, 42 <- c, 'b' <- b]@. Of course, when the labels occur in the order they are defined, we can just use the simpler desugaring. Note [Order of guards matters] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Similar to Note [Field match order for RecCon], the order in which the guards for a pattern match appear matter. Consider a situation similar to T5117: f (0:_) = () f (0:[]) = () The latter clause is clearly redundant. Yet if we translate the second clause as [x:xs' <- xs, [] <- xs', 0 <- x] We will say that the second clause only has an inaccessible RHS. That's because we force the tail of the list before comparing its head! So the correct translation would have been [x:xs' <- xs, 0 <- x, [] <- xs'] And we have to take in the guards on list cells into @mkListGrds@. Note [Countering exponential blowup] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Precise pattern match exhaustiveness checking is necessarily exponential in the size of some input programs. We implement a counter-measure in the form of the -fmax-pmcheck-models flag, limiting the number of Deltas we check against each pattern by a constant. How do we do that? Consider f True True = () f True True = () And imagine we set our limit to 1 for the sake of the example. The first clause will be checked against the initial Delta, {}. Doing so will produce an Uncovered set of size 2, containing the models {x/~True} and {x~True,y/~True}. Also we find the first clause to cover the model {x~True,y~True}. But the Uncovered set we get out of the match is too huge! We somehow have to ensure not to make things worse as they are already, so we continue checking with a singleton Uncovered set of the initial Delta {}. Why is this sound (wrt. notion of the GADTs Meet their Match paper)? Well, it basically amounts to forgetting that we matched against the first clause. The values represented by {} are a superset of those represented by its two refinements {x/~True} and {x~True,y/~True}. This forgetfulness becomes very apparent in the example above: By continuing with {} we don't detect the second clause as redundant, as it again covers the same non-empty subset of {}. So we don't flag everything as redundant anymore, but still will never flag something as redundant that isn't. For exhaustivity, the converse applies: We will report @f@ as non-exhaustive and report @f _ _@ as missing, which is a superset of the actual missing matches. But soundness means we will never fail to report a missing match. This mechanism is implemented in the higher-order function 'throttle'. Note [Combinatorial explosion in guards] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Function with many clauses and deeply nested guards like in #11195 tend to overwhelm the checker because they lead to exponential splitting behavior. See the comments on #11195 on refinement trees. Every guard refines the disjunction of Deltas by another split. This no different than the ConVar case, but in stark contrast we mostly don't get any useful information out of that split! Hence splitting k-fold just means having k-fold more work. The problem exacerbates for larger k, because it gets even more unlikely that we can handle all of the arising Deltas better than just continue working on the original Delta. We simply apply the same mechanism as in Note [Countering exponential blowup]. But we don't want to forget about actually useful info from pattern match clauses just because we had one clause with many guards. So we set the limit for guards much lower. Note [Translate CoPats] ~~~~~~~~~~~~~~~~~~~~~~~ The pattern match checker did not know how to handle coerced patterns `CoPat` efficiently, which gave rise to #11276. The original approach translated `CoPat`s: pat |> co ===> x (pat <- (x |> co)) Why did we do this seemingly unnecessary expansion in the first place? The reason is that the type of @pat |> co@ (which is the type of the value abstraction we match against) might be different than that of @pat@. Data instances such as @Sing (a :: Bool)@ are a good example of this: If we would just drop the coercion, we'd get a type error when matching @pat@ against its value abstraction, with the result being that pmIsSatisfiable decides that every possible data constructor fitting @pat@ is rejected as uninhabitated, leading to a lot of false warnings. But we can check whether the coercion is a hole or if it is just refl, in which case we can drop it. %************************************************************************ %* * Utilities for Pattern Match Checking %* * %************************************************************************ -} -- ---------------------------------------------------------------------------- -- * Basic utilities {- Note [Extensions to GADTs Meet Their Match] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The GADTs Meet Their Match paper presents the formalism that GHC's coverage checker adheres to. Since the paper's publication, there have been some additional features added to the coverage checker which are not described in the paper. This Note serves as a reference for these new features. * Value abstractions are severely simplified to the point where they are just variables. The information about the shape of a variable is encoded in the oracle state 'Delta' instead. * Handling of uninhabited fields like `!Void`. See Note [Strict argument type constraints] in GHC.HsToCore.PmCheck.Oracle. * Efficient handling of literal splitting, large enumerations and accurate redundancy warnings for `COMPLETE` groups through the oracle. Note [Filtering out non-matching COMPLETE sets] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Currently, conlikes in a COMPLETE set are simply grouped by the type constructor heading the return type. This is nice and simple, but it does mean that there are scenarios when a COMPLETE set might be incompatible with the type of a scrutinee. For instance, consider (from #14135): data Foo a = Foo1 a | Foo2 a pattern MyFoo2 :: Int -> Foo Int pattern MyFoo2 i = Foo2 i {-# COMPLETE Foo1, MyFoo2 #-} f :: Foo a -> a f (Foo1 x) = x `f` has an incomplete pattern-match, so when choosing which constructors to report as unmatched in a warning, GHC must choose between the original set of data constructors {Foo1, Foo2} and the COMPLETE set {Foo1, MyFoo2}. But observe that GHC shouldn't even consider the COMPLETE set as a possibility: the return type of MyFoo2, Foo Int, does not match the type of the scrutinee, Foo a, since there's no substitution `s` such that s(Foo Int) = Foo a. To ensure that GHC doesn't pick this COMPLETE set, it checks each pattern synonym constructor's return type matches the type of the scrutinee, and if one doesn't, then we remove the whole COMPLETE set from consideration. One might wonder why GHC only checks /pattern synonym/ constructors, and not /data/ constructors as well. The reason is because that the type of a GADT constructor very well may not match the type of a scrutinee, and that's OK. Consider this example (from #14059): data SBool (z :: Bool) where SFalse :: SBool False STrue :: SBool True pattern STooGoodToBeTrue :: forall (z :: Bool). () => z ~ True => SBool z pattern STooGoodToBeTrue = STrue {-# COMPLETE SFalse, STooGoodToBeTrue #-} wobble :: SBool z -> Bool wobble STooGoodToBeTrue = True In the incomplete pattern match for `wobble`, we /do/ want to warn that SFalse should be matched against, even though its type, SBool False, does not match the scrutinee type, SBool z. SG: Another angle at this is that the implied constraints when we instantiate universal type variables in the return type of a GADT will lead to *provided* thetas, whereas when we instantiate the return type of a pattern synonym that corresponds to a *required* theta. See Note [Pattern synonym result type] in PatSyn. Note how isValidCompleteMatches will successfully filter out pattern Just42 :: Maybe Int pattern Just42 = Just 42 But fail to filter out the equivalent pattern Just'42 :: (a ~ Int) => Maybe a pattern Just'42 = Just 42 Which seems fine as far as tcMatchTy is concerned, but it raises a few eye brows. -} {- %************************************************************************ %* * Heart of the algorithm: Function pmCheck %* * %************************************************************************ Main functions are: * pmCheck :: PatVec -> [PatVec] -> ValVec -> Delta -> DsM PartialResult This function implements functions `covered`, `uncovered` and `divergent` from the paper at once. Calls out to the auxilary function `pmCheckGuards` for handling (possibly multiple) guarded RHSs when the whole clause is checked. Slightly different from the paper because it does not even produce the covered and uncovered sets. Since we only care about whether a clause covers SOMETHING or if it may forces ANY argument, we only store a boolean in both cases, for efficiency. * pmCheckGuards :: [PatVec] -> ValVec -> Delta -> DsM PartialResult Processes the guards. -} -- | @throttle limit f n delta@ executes the pattern match action @f@ but -- replaces the 'Uncovered' set by @[delta]@ if not doing so would lead to -- too many Deltas to check. -- -- See Note [Countering exponential blowup] and -- Note [Combinatorial explosion in guards] -- -- How many is "too many"? @throttle@ assumes that the pattern match action -- will be executed against @n@ similar other Deltas, its "siblings". Now, by -- observing the branching factor (i.e. the number of children) of executing -- the action, we can estimate how many Deltas there would be in the next -- generation. If we find that this number exceeds @limit@, we do -- "birth control": We simply don't allow a branching factor of more than 1. -- Otherwise we just return the singleton set of the original @delta@. -- This amounts to forgetting about the refined facts we got from running the -- action. throttle :: Int -> (Int -> Delta -> DsM PartialResult) -> Int -> Delta -> DsM (Int, PartialResult) throttle limit f n_siblings delta = do res <- f n_siblings delta let n_own_children = length (presultUncovered res) let n_next_gen = n_siblings * n_own_children -- Birth control! if n_next_gen <= limit || n_own_children <= 1 then pure (n_next_gen, res) else pure (n_siblings, res { presultUncovered = [delta], presultApprox = Approximate }) -- | Map a pattern matching action processing a single 'Delta' over a -- 'Uncovered' set and return the combined 'PartialResult's. runMany :: (Delta -> DsM PartialResult) -> Uncovered -> DsM PartialResult runMany f unc = mconcat <$> traverse f unc -- | Print diagnostic info and actually call 'pmCheck''. pmCheck :: GrdVec -> [GrdVec] -> Int -> Delta -> DsM PartialResult pmCheck ps guards n delta = do tracePm "pmCheck {" $ vcat [ ppr n <> colon , hang (text "patterns:") 2 (ppr ps) , hang (text "guards:") 2 (ppr guards) , ppr delta ] res <- pmCheck' ps guards n delta tracePm "}:" (ppr res) -- braces are easier to match by tooling return res -- | Lifts 'pmCheck' over a 'DsM (Maybe Delta)'. pmCheckM :: GrdVec -> [GrdVec] -> Int -> DsM (Maybe Delta) -> DsM PartialResult pmCheckM ps guards n m_mb_delta = m_mb_delta >>= \case Nothing -> pure mempty Just delta -> pmCheck ps guards n delta -- | Check the list of mutually exclusive guards pmCheckGuards :: [GrdVec] -> Int -> Delta -> DsM PartialResult pmCheckGuards [] _ delta = return (usimple delta) pmCheckGuards (gv:gvs) n delta = do dflags <- getDynFlags let limit = maxPmCheckModels dflags `div` 5 (n', PartialResult cs unc ds pc) <- throttle limit (pmCheck gv []) n delta (PartialResult css uncs dss pcs) <- runMany (pmCheckGuards gvs n') unc return $ PartialResult (cs `mappend` css) uncs (ds `mappend` dss) (pc `mappend` pcs) -- | Matching function: Check simultaneously a clause (takes separately the -- patterns and the list of guards) for exhaustiveness, redundancy and -- inaccessibility. pmCheck' :: GrdVec -- ^ Patterns of the clause -> [GrdVec] -- ^ (Possibly multiple) guards of the clause -> Int -- ^ Estimate on the number of similar 'Delta's to handle. -- See 6. in Note [Countering exponential blowup] -> Delta -- ^ Oracle state giving meaning to the identifiers in the ValVec -> DsM PartialResult pmCheck' [] guards n delta | null guards = return $ mempty { presultCovered = Covered } | otherwise = pmCheckGuards guards n delta -- let x = e: Add x ~ e to the oracle pmCheck' (PmLet { pm_id = x, pm_let_expr = e } : ps) guards n delta = do tracePm "PmLet" (vcat [ppr x, ppr e]) -- x is fresh because it's bound by the let delta' <- expectJust "x is fresh" <$> addVarCoreCt delta x e pmCheck ps guards n delta' -- Bang x: Add x /~ _|_ to the oracle pmCheck' (PmBang x : ps) guards n delta = do tracePm "PmBang" (ppr x) pr <- pmCheckM ps guards n (addTmCt delta (TmVarNonVoid x)) pure (forceIfCanDiverge delta x pr) -- Con: Add x ~ K ys to the Covered set and x /~ K to the Uncovered set pmCheck' (p : ps) guards n delta | PmCon{ pm_id = x, pm_con_con = con, pm_con_args = args , pm_con_dicts = dicts } <- p = do -- E.g f (K p q) = -- -- Split delta into two refinements: -- * one for , binding x to (K p q) -- * one for , recording that x is /not/ (K _ _) -- Stuff for pr_pos <- pmCheckM ps guards n (addPmConCts delta x con dicts args) -- The var is forced regardless of whether @con@ was satisfiable -- See Note [Divergence of Newtype matches] let pr_pos' = addConMatchStrictness delta x con pr_pos -- Stuff for pr_neg <- addRefutableAltCon delta x con >>= \case Nothing -> pure mempty Just delta' -> pure (usimple delta') tracePm "PmCon" (vcat [ppr p, ppr x, ppr pr_pos', ppr pr_neg]) -- Combine both into a single PartialResult let pr = mkUnion pr_pos' pr_neg pure pr addPmConCts :: Delta -> Id -> PmAltCon -> [EvVar] -> [Id] -> DsM (Maybe Delta) addPmConCts delta x con dicts fields = runMaybeT $ do delta_ty <- MaybeT $ addTypeEvidence delta (listToBag dicts) delta_tm_ty <- MaybeT $ addTmCt delta_ty (TmVarCon x con fields) pure delta_tm_ty -- ---------------------------------------------------------------------------- -- * Utilities for main checking -- | Initialise with default values for covering and divergent information and -- a singleton uncovered set. usimple :: Delta -> PartialResult usimple delta = mempty { presultUncovered = [delta] } -- | Get the union of two covered, uncovered and divergent value set -- abstractions. Since the covered and divergent sets are represented by a -- boolean, union means computing the logical or (at least one of the two is -- non-empty). mkUnion :: PartialResult -> PartialResult -> PartialResult mkUnion = mappend -- | Set the divergent set to not empty forces :: PartialResult -> PartialResult forces pres = pres { presultDivergent = Diverged } -- | Set the divergent set to non-empty if the variable has not been forced yet forceIfCanDiverge :: Delta -> Id -> PartialResult -> PartialResult forceIfCanDiverge delta x | canDiverge delta x = forces | otherwise = id -- | 'forceIfCanDiverge' if the 'PmAltCon' was not a Newtype. -- See Note [Divergence of Newtype matches]. addConMatchStrictness :: Delta -> Id -> PmAltCon -> PartialResult -> PartialResult addConMatchStrictness _ _ (PmAltConLike (RealDataCon dc)) res | isNewTyCon (dataConTyCon dc) = res addConMatchStrictness delta x _ res = forceIfCanDiverge delta x res -- ---------------------------------------------------------------------------- -- * Propagation of term constraints inwards when checking nested matches {- Note [Type and Term Equality Propagation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When checking a match it would be great to have all type and term information available so we can get more precise results. For this reason we have functions `addDictsDs' and `addTmVarCsDs' in DsMonad that store in the environment type and term constraints (respectively) as we go deeper. The type constraints we propagate inwards are collected by `collectEvVarsPats' in GHC.Hs.Pat. This handles bug #4139 ( see example https://gitlab.haskell.org/ghc/ghc/snippets/672 ) where this is needed. For term equalities we do less, we just generate equalities for HsCase. For example we accurately give 2 redundancy warnings for the marked cases: f :: [a] -> Bool f x = case x of [] -> case x of -- brings (x ~ []) in scope [] -> True (_:_) -> False -- can't happen (_:_) -> case x of -- brings (x ~ (_:_)) in scope (_:_) -> True [] -> False -- can't happen Functions `addScrutTmCs' and `addPatTmCs' are responsible for generating these constraints. -} locallyExtendPmDelta :: (Delta -> DsM (Maybe Delta)) -> DsM a -> DsM a locallyExtendPmDelta ext k = getPmDelta >>= ext >>= \case -- If adding a constraint would lead to a contradiction, don't add it. -- See @Note [Recovering from unsatisfiable pattern-matching constraints]@ -- for why this is done. Nothing -> k Just delta' -> updPmDelta delta' k -- | Add in-scope type constraints addTyCsDs :: Bag EvVar -> DsM a -> DsM a addTyCsDs ev_vars = locallyExtendPmDelta (\delta -> addTypeEvidence delta ev_vars) -- | Add equalities for the scrutinee to the local 'DsM' environment when -- checking a case expression: -- case e of x { matches } -- When checking matches we record that (x ~ e) where x is the initial -- uncovered. All matches will have to satisfy this equality. addScrutTmCs :: Maybe (LHsExpr GhcTc) -> [Id] -> DsM a -> DsM a addScrutTmCs Nothing _ k = k addScrutTmCs (Just scr) [x] k = do scr_e <- dsLExpr scr locallyExtendPmDelta (\delta -> addVarCoreCt delta x scr_e) k addScrutTmCs _ _ _ = panic "addScrutTmCs: HsCase with more than one case binder" -- | Add equalities to the local 'DsM' environment when checking the RHS of a -- case expression: -- case e of x { p1 -> e1; ... pn -> en } -- When we go deeper to check e.g. e1 we record (x ~ p1). addPatTmCs :: [Pat GhcTc] -- LHS (should have length 1) -> [Id] -- MatchVars (should have length 1) -> DsM a -> DsM a -- Computes an approximation of the Covered set for p1 (which pmCheck currently -- discards). addPatTmCs ps xs k = do fam_insts <- dsGetFamInstEnvs grds <- concat <$> zipWithM (translatePat fam_insts) xs ps locallyExtendPmDelta (\delta -> computeCovered grds delta) k -- | A dead simple version of 'pmCheck' that only computes the Covered set. -- So it only cares about collecting positive info. -- We use it to collect info from a pattern when we check its RHS. -- See 'addPatTmCs'. computeCovered :: GrdVec -> Delta -> DsM (Maybe Delta) -- The duplication with 'pmCheck' is really unfortunate, but it's simpler than -- separating out the common cases with 'pmCheck', because that would make the -- ConVar case harder to understand. computeCovered [] delta = pure (Just delta) computeCovered (PmLet { pm_id = x, pm_let_expr = e } : ps) delta = do delta' <- expectJust "x is fresh" <$> addVarCoreCt delta x e computeCovered ps delta' computeCovered (PmBang{} : ps) delta = do computeCovered ps delta computeCovered (p : ps) delta | PmCon{ pm_id = x, pm_con_con = con, pm_con_args = args , pm_con_dicts = dicts } <- p = addPmConCts delta x con dicts args >>= \case Nothing -> pure Nothing Just delta' -> computeCovered ps delta' {- %************************************************************************ %* * Pretty printing of exhaustiveness/redundancy check warnings %* * %************************************************************************ -} -- | Check whether any part of pattern match checking is enabled for this -- 'HsMatchContext' (does not matter whether it is the redundancy check or the -- exhaustiveness check). isMatchContextPmChecked :: DynFlags -> Origin -> HsMatchContext id -> Bool isMatchContextPmChecked dflags origin kind | isGenerated origin = False | otherwise = wopt Opt_WarnOverlappingPatterns dflags || exhaustive dflags kind -- | Return True when any of the pattern match warnings ('allPmCheckWarnings') -- are enabled, in which case we need to run the pattern match checker. needToRunPmCheck :: DynFlags -> Origin -> Bool needToRunPmCheck dflags origin | isGenerated origin = False | otherwise = notNull (filter (`wopt` dflags) allPmCheckWarnings) -- | Issue all the warnings (coverage, exhaustiveness, inaccessibility) dsPmWarn :: DynFlags -> DsMatchContext -> [Id] -> PmResult -> DsM () dsPmWarn dflags ctx@(DsMatchContext kind loc) vars pm_result = when (flag_i || flag_u) $ do let exists_r = flag_i && notNull redundant exists_i = flag_i && notNull inaccessible && not is_rec_upd exists_u = flag_u && notNull uncovered approx = precision == Approximate when (approx && (exists_u || exists_i)) $ putSrcSpanDs loc (warnDs NoReason approx_msg) when exists_r $ forM_ redundant $ \(dL->L l q) -> do putSrcSpanDs l (warnDs (Reason Opt_WarnOverlappingPatterns) (pprEqn q "is redundant")) when exists_i $ forM_ inaccessible $ \(dL->L l q) -> do putSrcSpanDs l (warnDs (Reason Opt_WarnOverlappingPatterns) (pprEqn q "has inaccessible right hand side")) when exists_u $ putSrcSpanDs loc $ warnDs flag_u_reason $ pprEqns vars uncovered where PmResult { pmresultRedundant = redundant , pmresultUncovered = uncovered , pmresultInaccessible = inaccessible , pmresultApproximate = precision } = pm_result flag_i = wopt Opt_WarnOverlappingPatterns dflags flag_u = exhaustive dflags kind flag_u_reason = maybe NoReason Reason (exhaustiveWarningFlag kind) is_rec_upd = case kind of { RecUpd -> True; _ -> False } -- See Note [Inaccessible warnings for record updates] maxPatterns = maxUncoveredPatterns dflags -- Print a single clause (for redundant/with-inaccessible-rhs) pprEqn q txt = pprContext True ctx (text txt) $ \f -> f (pprPats kind (map unLoc q)) -- Print several clauses (for uncovered clauses) pprEqns vars deltas = pprContext False ctx (text "are non-exhaustive") $ \_ -> case vars of -- See #11245 [] -> text "Guards do not cover entire pattern space" _ -> let us = map (\delta -> pprUncovered delta vars) deltas in hang (text "Patterns not matched:") 4 (vcat (take maxPatterns us) $$ dots maxPatterns us) approx_msg = vcat [ hang (text "Pattern match checker ran into -fmax-pmcheck-models=" <> int (maxPmCheckModels dflags) <> text " limit, so") 2 ( bullet <+> text "Redundant clauses might not be reported at all" $$ bullet <+> text "Redundant clauses might be reported as inaccessible" $$ bullet <+> text "Patterns reported as unmatched might actually be matched") , text "Increase the limit or resolve the warnings to suppress this message." ] {- Note [Inaccessible warnings for record updates] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider (#12957) data T a where T1 :: { x :: Int } -> T Bool T2 :: { x :: Int } -> T a T3 :: T a f :: T Char -> T a f r = r { x = 3 } The desugarer will (conservatively generate a case for T1 even though it's impossible: f r = case r of T1 x -> T1 3 -- Inaccessible branch T2 x -> T2 3 _ -> error "Missing" We don't want to warn about the inaccessible branch because the programmer didn't put it there! So we filter out the warning here. -} dots :: Int -> [a] -> SDoc dots maxPatterns qs | qs `lengthExceeds` maxPatterns = text "..." | otherwise = empty -- | All warning flags that need to run the pattern match checker. allPmCheckWarnings :: [WarningFlag] allPmCheckWarnings = [ Opt_WarnIncompletePatterns , Opt_WarnIncompleteUniPatterns , Opt_WarnIncompletePatternsRecUpd , Opt_WarnOverlappingPatterns ] -- | Check whether the exhaustiveness checker should run (exhaustiveness only) exhaustive :: DynFlags -> HsMatchContext id -> Bool exhaustive dflags = maybe False (`wopt` dflags) . exhaustiveWarningFlag -- | Denotes whether an exhaustiveness check is supported, and if so, -- via which 'WarningFlag' it's controlled. -- Returns 'Nothing' if check is not supported. exhaustiveWarningFlag :: HsMatchContext id -> Maybe WarningFlag exhaustiveWarningFlag (FunRhs {}) = Just Opt_WarnIncompletePatterns exhaustiveWarningFlag CaseAlt = Just Opt_WarnIncompletePatterns exhaustiveWarningFlag IfAlt = Just Opt_WarnIncompletePatterns exhaustiveWarningFlag LambdaExpr = Just Opt_WarnIncompleteUniPatterns exhaustiveWarningFlag PatBindRhs = Just Opt_WarnIncompleteUniPatterns exhaustiveWarningFlag PatBindGuards = Just Opt_WarnIncompletePatterns exhaustiveWarningFlag ProcExpr = Just Opt_WarnIncompleteUniPatterns exhaustiveWarningFlag RecUpd = Just Opt_WarnIncompletePatternsRecUpd exhaustiveWarningFlag ThPatSplice = Nothing exhaustiveWarningFlag PatSyn = Nothing exhaustiveWarningFlag ThPatQuote = Nothing exhaustiveWarningFlag (StmtCtxt {}) = Nothing -- Don't warn about incomplete patterns -- in list comprehensions, pattern guards -- etc. They are often *supposed* to be -- incomplete -- True <==> singular pprContext :: Bool -> DsMatchContext -> SDoc -> ((SDoc -> SDoc) -> SDoc) -> SDoc pprContext singular (DsMatchContext kind _loc) msg rest_of_msg_fun = vcat [text txt <+> msg, sep [ text "In" <+> ppr_match <> char ':' , nest 4 (rest_of_msg_fun pref)]] where txt | singular = "Pattern match" | otherwise = "Pattern match(es)" (ppr_match, pref) = case kind of FunRhs { mc_fun = (dL->L _ fun) } -> (pprMatchContext kind, \ pp -> ppr fun <+> pp) _ -> (pprMatchContext kind, \ pp -> pp) pprPats :: HsMatchContext Name -> [Pat GhcTc] -> SDoc pprPats kind pats = sep [sep (map ppr pats), matchSeparator kind, text "..."]