[Git][ghc/ghc][wip/T18626] PmCheck: Long-distance information for LocalBinds (#18626)
Sebastian Graf
gitlab at gitlab.haskell.org
Tue Sep 29 11:33:23 UTC 2020
Sebastian Graf pushed to branch wip/T18626 at Glasgow Haskell Compiler / GHC
Commits:
88197973 by Sebastian Graf at 2020-09-29T13:33:15+02:00
PmCheck: Long-distance information for LocalBinds (#18626)
Now `desugarLocalBind` (formerly `desugarLet`) reasons about
* `FunBind`s that
* Have no pattern matches (so which aren't functions)
* Have a singleton match group with a single GRHS
* (which may have guards)
* and looks through trivial post-typechecking `AbsBinds` in doing so
to pick up the introduced renamings.
And desugars to `PmLet` LYG-style guards. Since GRHSs are no longer
denoted simply by `NonEmpty PmGRHS`, but also need to carry a `[PmGrd]`
for the `PmLet`s from `LocalBind`s, I added `PmGRHSs` to capture that.
Since we call out to the desugarer more often, I found that there were
superfluous warnings emitted when desugaring e.g. case expressions.
Thus, I made sure that we deactivate any warnings in the LYG desugaring
steps by the new wrapper function `noCheckDs`.
There's a regression test in `T18626`. Fixes #18626.
- - - - -
6 changed files:
- compiler/GHC/HsToCore/Pmc.hs
- compiler/GHC/HsToCore/Pmc/Check.hs
- compiler/GHC/HsToCore/Pmc/Desugar.hs
- compiler/GHC/HsToCore/Pmc/Types.hs
- + testsuite/tests/pmcheck/should_compile/T18626.hs
- testsuite/tests/pmcheck/should_compile/all.T
Changes:
=====================================
compiler/GHC/HsToCore/Pmc.hs
=====================================
@@ -59,6 +59,7 @@ import GHC.HsToCore.Pmc.Ppr
import GHC.Types.Basic (Origin(..))
import GHC.Core (CoreExpr)
import GHC.Driver.Session
+import GHC.Driver.Types
import GHC.Hs
import GHC.Types.Id
import GHC.Types.SrcLoc
@@ -66,11 +67,12 @@ import GHC.Utils.Misc
import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Types.Var (EvVar)
+import GHC.Tc.Types
import GHC.Tc.Utils.TcType (evVarPred)
import {-# SOURCE #-} GHC.HsToCore.Expr (dsLExpr)
import GHC.HsToCore.Monad
import GHC.Data.Bag
-import GHC.Data.IOEnv (unsafeInterleaveM)
+import GHC.Data.IOEnv (updEnv, unsafeInterleaveM)
import GHC.Data.OrdList
import GHC.Utils.Monad (mapMaybeM)
@@ -95,12 +97,22 @@ getLdiNablas = do
True -> pure nablas
False -> pure initNablas
+-- | We need to call the Hs desugarer to get the Core of a let-binding or where
+-- clause. We don't want to run the coverage checker when doing so! Efficiency
+-- is one concern, but also a lack of properly set up long-distance information
+-- might trigger warnings that we normally wouldn't emit.
+noCheckDs :: DsM a -> DsM a
+noCheckDs k = do
+ dflags <- getDynFlags
+ let dflags' = foldl' wopt_unset dflags allPmCheckWarnings
+ updEnv (\env -> env{env_top = (env_top env) {hsc_dflags = dflags'} }) k
+
-- | Check a pattern binding (let, where) for exhaustiveness.
pmcPatBind :: DsMatchContext -> Id -> Pat GhcTc -> DsM ()
-- See Note [pmcPatBind only checks PatBindRhs]
pmcPatBind ctxt@(DsMatchContext PatBindRhs loc) var p = do
- missing <- getLdiNablas
- pat_bind <- desugarPatBind loc var p
+ !missing <- getLdiNablas
+ pat_bind <- noCheckDs $ desugarPatBind loc var p
tracePm "pmcPatBind {" (vcat [ppr ctxt, ppr var, ppr p, ppr pat_bind, ppr missing])
result <- unCA (checkPatBind pat_bind) missing
tracePm "}: " (ppr (cr_uncov result))
@@ -117,8 +129,8 @@ pmcGRHSs
pmcGRHSs hs_ctxt guards@(GRHSs _ grhss _) = do
let combined_loc = foldl1 combineSrcSpans (map getLoc grhss)
ctxt = DsMatchContext hs_ctxt combined_loc
- matches <- desugarGRHSs combined_loc empty guards
- missing <- getLdiNablas
+ !missing <- getLdiNablas
+ matches <- noCheckDs $ desugarGRHSs combined_loc empty guards
tracePm "pmcGRHSs" (hang (vcat [ppr ctxt
, text "Guards:"])
2
@@ -126,7 +138,7 @@ pmcGRHSs hs_ctxt guards@(GRHSs _ grhss _) = do
result <- unCA (checkGRHSs matches) missing
tracePm "}: " (ppr (cr_uncov result))
formatReportWarnings cirbsGRHSs ctxt [] result
- return (ldiGRHS <$> cr_ret result)
+ return (ldiGRHSs (cr_ret result))
-- | Check a list of syntactic 'Match'es (part of case, functions, etc.), each
-- with a 'Pat' and one or more 'GRHSs':
@@ -153,7 +165,7 @@ pmcMatches ctxt vars matches = do
-- We have to force @missing@ before printing out the trace message,
-- otherwise we get interleaved output from the solver. This function
-- should be strict in @missing@ anyway!
- !missing <- getLdiNablas
+ !missing <- getLdiNablas
tracePm "pmcMatches {" $
hang (vcat [ppr ctxt, ppr vars, text "Matches:"])
2
@@ -162,13 +174,13 @@ pmcMatches ctxt vars matches = do
Nothing -> do
-- This must be an -XEmptyCase. See Note [Checking EmptyCase]
let var = only vars
- empty_case <- desugarEmptyCase var
+ empty_case <- noCheckDs $ desugarEmptyCase var
result <- unCA (checkEmptyCase empty_case) missing
tracePm "}: " (ppr (cr_uncov result))
formatReportWarnings cirbsEmptyCase ctxt vars result
return []
Just matches -> do
- matches <- desugarMatches vars matches
+ matches <- noCheckDs $ desugarMatches vars matches
result <- unCA (checkMatchGroup matches) missing
tracePm "}: " (ppr (cr_uncov result))
formatReportWarnings cirbsMatchGroup ctxt vars result
@@ -201,7 +213,10 @@ ldiMatchGroup (PmMatchGroup matches) = ldiMatch <$> matches
ldiMatch :: PmMatch Post -> (Nablas, NonEmpty Nablas)
ldiMatch (PmMatch { pm_pats = red, pm_grhss = grhss }) =
- (rs_cov red, ldiGRHS <$> grhss)
+ (rs_cov red, ldiGRHSs grhss)
+
+ldiGRHSs :: PmGRHSs Post -> NonEmpty Nablas
+ldiGRHSs (PmGRHSs { pgs_grhss = grhss }) = ldiGRHS <$> grhss
ldiGRHS :: PmGRHS Post -> Nablas
ldiGRHS (PmGRHS { pg_grds = red }) = rs_cov red
@@ -277,8 +292,8 @@ cirbsMatch PmMatch { pm_pats = red, pm_grhss = grhss } = do
$ applyWhen (not is_covered) markAllRedundant
$ cirb
-cirbsGRHSs :: NonEmpty (PmGRHS Post) -> DsM CIRB
-cirbsGRHSs grhss = Semi.sconcat <$> traverse cirbsGRHS grhss
+cirbsGRHSs :: PmGRHSs Post -> DsM CIRB
+cirbsGRHSs (PmGRHSs { pgs_grhss = grhss }) = Semi.sconcat <$> traverse cirbsGRHS grhss
cirbsGRHS :: PmGRHS Post -> DsM CIRB
cirbsGRHS PmGRHS { pg_grds = red, pg_rhs = info } = do
=====================================
compiler/GHC/HsToCore/Pmc/Check.hs
=====================================
@@ -167,8 +167,9 @@ checkMatch :: PmMatch Pre -> CheckAction (PmMatch Post)
checkMatch (PmMatch { pm_pats = GrdVec grds, pm_grhss = grhss }) =
leftToRight PmMatch (checkGrds grds) (checkGRHSs grhss)
-checkGRHSs :: NonEmpty (PmGRHS Pre) -> CheckAction (NonEmpty (PmGRHS Post))
-checkGRHSs = checkSequence checkGRHS
+checkGRHSs :: PmGRHSs Pre -> CheckAction (PmGRHSs Post)
+checkGRHSs (PmGRHSs { pgs_lcls = GrdVec lcls, pgs_grhss = grhss }) =
+ leftToRight PmGRHSs (checkGrds lcls) (checkSequence checkGRHS grhss)
checkGRHS :: PmGRHS Pre -> CheckAction (PmGRHS Post)
checkGRHS (PmGRHS { pg_grds = GrdVec grds, pg_rhs = rhs_info }) =
=====================================
compiler/GHC/HsToCore/Pmc/Desugar.hs
=====================================
@@ -26,6 +26,7 @@ import GHC.HsToCore.Pmc.Types
import GHC.HsToCore.Pmc.Utils
import GHC.Core (Expr(Var,App))
import GHC.Data.FastString (unpackFS, lengthFS)
+import GHC.Data.Bag (bagToList)
import GHC.Driver.Session
import GHC.Hs
import GHC.Tc.Utils.Zonk (shortCutLit)
@@ -36,6 +37,7 @@ import GHC.Builtin.Types
import GHC.Types.SrcLoc
import GHC.Utils.Outputable
import GHC.Utils.Panic
+import GHC.Utils.Misc
import GHC.Core.DataCon
import GHC.Types.Var (EvVar)
import GHC.Core.Coercion
@@ -326,12 +328,14 @@ desugarMatch vars (L match_loc (Match { m_pats = pats, m_grhss = grhss })) = do
-- tracePm "desugarMatch" (vcat [ppr pats, ppr pats', ppr grhss'])
return PmMatch { pm_pats = GrdVec pats', pm_grhss = grhss' }
-desugarGRHSs :: SrcSpan -> SDoc -> GRHSs GhcTc (LHsExpr GhcTc) -> DsM (NonEmpty (PmGRHS Pre))
-desugarGRHSs match_loc pp_pats grhss
- = traverse (desugarLGRHS match_loc pp_pats)
- . expectJust "desugarGRHSs"
- . NE.nonEmpty
- $ grhssGRHSs grhss
+desugarGRHSs :: SrcSpan -> SDoc -> GRHSs GhcTc (LHsExpr GhcTc) -> DsM (PmGRHSs Pre)
+desugarGRHSs match_loc pp_pats grhss = do
+ lcls <- desugarLocalBinds (grhssLocalBinds grhss)
+ grhss' <- traverse (desugarLGRHS match_loc pp_pats)
+ . expectJust "desugarGRHSs"
+ . NE.nonEmpty
+ $ grhssGRHSs grhss
+ return PmGRHSs { pgs_lcls = GrdVec lcls, pgs_grhss = grhss' }
-- | Desugar a guarded right-hand side to a single 'GrdTree'
desugarLGRHS :: SrcSpan -> SDoc -> LGRHS GhcTc (LHsExpr GhcTc) -> DsM (PmGRHS Pre)
@@ -351,7 +355,7 @@ desugarLGRHS match_loc pp_pats (L _loc (GRHS _ gs _)) = do
desugarGuard :: GuardStmt GhcTc -> DsM [PmGrd]
desugarGuard guard = case guard of
BodyStmt _ e _ _ -> desugarBoolGuard e
- LetStmt _ binds -> desugarLet (unLoc binds)
+ LetStmt _ binds -> desugarLocalBinds binds
BindStmt _ p e -> desugarBind p e
LastStmt {} -> panic "desugarGuard LastStmt"
ParStmt {} -> panic "desugarGuard ParStmt"
@@ -359,9 +363,39 @@ desugarGuard guard = case guard of
RecStmt {} -> panic "desugarGuard RecStmt"
ApplicativeStmt {} -> panic "desugarGuard ApplicativeLastStmt"
--- | Desugar let-bindings
-desugarLet :: HsLocalBinds GhcTc -> DsM [PmGrd]
-desugarLet _binds = return []
+-- | Desugar local bindings to a bunch of 'PmLet' guards.
+-- Deals only with simple @let@ or @where@ bindings without any polymorphism,
+-- recursion, pattern bindings etc.
+-- See Note [Long-distance information for HsLocalBinds].
+desugarLocalBinds :: LHsLocalBinds GhcTc -> DsM [PmGrd]
+desugarLocalBinds (L _ (HsValBinds _ (XValBindsLR (NValBinds binds _)))) = do
+ concatMapM (concatMapM go . bagToList) (map snd binds)
+ where
+ go :: LHsBind GhcTc -> DsM [PmGrd]
+ go (L _ FunBind{fun_id = L _ x, fun_matches = mg})
+ -- See Note [Long-distance information for HsLocalBinds] for why this
+ -- pattern match is so very specific.
+ | L _ [L _ Match{m_pats = [], m_grhss = grhss}] <- mg_alts mg
+ , GRHSs{grhssGRHSs = [L _ (GRHS _ _grds rhs)]} <- grhss = do
+ core_rhs <- dsLExpr rhs
+ return [PmLet x core_rhs]
+ go (L _ AbsBinds{ abs_tvs = [], abs_ev_vars = []
+ , abs_exports=exports, abs_binds = binds }) = do
+ -- Typechecked HsLocalBinds are wrapped in AbsBinds, which carry
+ -- renamings. See Note [Long-distance information for HsLocalBinds]
+ -- for the details.
+ let go_export :: ABExport GhcTc -> Maybe PmGrd
+ go_export ABE{abe_poly = x, abe_mono = y, abe_wrap = wrap}
+ | isIdHsWrapper wrap
+ = ASSERT2(idType x `eqType` idType y, ppr x $$ ppr (idType x) $$ ppr y $$ ppr (idType y))
+ Just $ PmLet x (Var y)
+ | otherwise
+ = Nothing
+ let exps = mapMaybe go_export exports
+ bs <- concatMapM go (bagToList binds)
+ return (exps ++ bs)
+ go _ = return []
+desugarLocalBinds _binds = return []
-- | Desugar a pattern guard
-- @pat <- e ==> let x = e; <guards for pat <- x>@
@@ -447,4 +481,43 @@ 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.
+
+Note [Long-distance information for HsLocalBinds]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider (#18626)
+
+ f :: Int -> ()
+ f x | y = ()
+ where
+ y = True
+
+ x :: ()
+ x | let y = True, y = ()
+
+Both definitions are exhaustive, but to make the necessary long-distance
+connection from @y@'s binding to its use site in a guard, we have to collect
+'PmLet' guards for the 'HsLocalBinds' which contain @y@'s definitions.
+
+In principle, we are only interested in desugaring local binds that are
+'FunBind's, that
+
+ * Have no pattern matches. If @y@ above had any patterns, it would be a
+ function and we can't reason about them anyway.
+ * Have singleton match group with a single GRHS.
+ Otherwise, what expression to pick in the generated guard @let y = <rhs>@?
+
+It turns out that desugaring type-checked local binds in this way is a bit
+more complex than expected: Apparently, all bindings are wrapped in 'AbsBinds'
+Nfter type-checking. See Note [AbsBinds] in "GHC.Hs.Binds".
+
+We make sure that there is no polymorphism in the way by checking that there
+are no 'abs_tvs' or 'abs_ev_vars' (we don't reason about
+ at y :: forall a. Eq a => ...@) and that the exports carry no 'HsWrapper's. In
+this case, the exports are a simple renaming substitution that we can capture
+with 'PmLet'. Ultimately we'll hit those renamed 'FunBind's, though, which is
+the whole point.
+
+The place to store the 'PmLet' guards for @where@ clauses (which are per
+'GRHSs') is as a field of 'PmGRHSs'. For plain @let@ guards as in the guards of
+ at x@, we can simply add them to the 'pg_grds' field of 'PmGRHS'.
-}
=====================================
compiler/GHC/HsToCore/Pmc/Types.hs
=====================================
@@ -22,7 +22,7 @@ module GHC.HsToCore.Pmc.Types (
SrcInfo(..), PmGrd(..), GrdVec(..),
-- ** Guard tree language
- PmMatchGroup(..), PmMatch(..), PmGRHS(..), PmPatBind(..), PmEmptyCase(..),
+ PmMatchGroup(..), PmMatch(..), PmGRHSs(..), PmGRHS(..), PmPatBind(..), PmEmptyCase(..),
-- * Coverage Checking types
RedSets (..), Precision (..), CheckResult (..),
@@ -112,7 +112,13 @@ newtype PmMatchGroup p = PmMatchGroup (NonEmpty (PmMatch p))
-- | A guard tree denoting 'Match': A payload describing the pats and a bunch of
-- GRHS.
-data PmMatch p = PmMatch { pm_pats :: !p, pm_grhss :: !(NonEmpty (PmGRHS p)) }
+data PmMatch p = PmMatch { pm_pats :: !p, pm_grhss :: !(PmGRHSs p) }
+
+-- | A guard tree denoting 'GRHSs': A bunch of 'PmLet' guards for local
+-- bindings from the 'GRHSs's @where@ clauses and the actual list of 'GRHS'.
+-- See Note [Long-distance information for HsLocalBinds] in
+-- "GHC.HsToCore.Pmc.Desugar".
+data PmGRHSs p = PmGRHSs { pgs_lcls :: !p, pgs_grhss :: !(NonEmpty (PmGRHS p))}
-- | A guard tree denoting 'GRHS': A payload describing the grds and a 'SrcInfo'
-- useful for printing out in warnings messages.
@@ -149,6 +155,10 @@ instance Outputable p => Outputable (PmMatch p) where
ppr (PmMatch { pm_pats = grds, pm_grhss = grhss }) =
ppr grds <+> ppr grhss
+instance Outputable p => Outputable (PmGRHSs p) where
+ ppr (PmGRHSs { pgs_lcls = _lcls, pgs_grhss = grhss }) =
+ ppr grhss
+
instance Outputable p => Outputable (PmGRHS p) where
ppr (PmGRHS { pg_grds = grds, pg_rhs = rhs }) =
ppr grds <+> text "->" <+> ppr rhs
=====================================
testsuite/tests/pmcheck/should_compile/T18626.hs
=====================================
@@ -0,0 +1,11 @@
+{-# OPTIONS_GHC -Wincomplete-patterns -fforce-recomp #-}
+
+module Lib where
+
+x :: ()
+x | let y = True, y = ()
+
+f :: Int -> ()
+f _ | y = ()
+ where
+ y = True
=====================================
testsuite/tests/pmcheck/should_compile/all.T
=====================================
@@ -148,6 +148,8 @@ test('T18478', collect_compiler_stats('bytes allocated',10), compile,
['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
test('T18533', normal, compile,
['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
+test('T18626', normal, compile,
+ ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
test('T18572', normal, compile,
['-fwarn-incomplete-patterns -fwarn-incomplete-uni-patterns -fwarn-overlapping-patterns'])
test('T18609', normal, compile,
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/8819797310092d120eeaf05310e7e01a800b5d7d
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/8819797310092d120eeaf05310e7e01a800b5d7d
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