Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

5 changed files:

Changes:

  • changelog.d/fix-duplicate-pmc-warnings
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    +section: compiler
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    +synopsis: Fix duplicate desugaring warnings emitted by the pattern match checker.
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    +  The pattern match checker now suppresses warnings that are already reported
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    +  by the main desugaring pass.
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    +issues: #25996
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    +mrs: !15859

  • compiler/GHC/HsToCore/Pmc/Desugar.hs
    ... ... @@ -375,16 +375,18 @@ desugarConPatOut x con univ_tys ex_tvs dicts = \case
    375 375
    376 376 
     desugarPatBind :: SrcSpan -> Id -> Pat GhcTc -> DsM (PmPatBind Pre)
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     -- See 'GrdPatBind' for how this simply repurposes GrdGRHS.
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    -desugarPatBind loc var pat =
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    +-- See Note [Suppress warnings in PMC desugaring]
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    +desugarPatBind loc var pat = discardWarningsDs $
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       PmPatBind . flip PmGRHS (SrcInfo (L loc (ppr pat))) <$> desugarPat var pat
    380 381
    381 382 
     desugarEmptyCase :: Id -> DsM PmEmptyCase
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     desugarEmptyCase var = pure PmEmptyCase { pe_var = var }
    383 384
    384 385 
     -- | Desugar the non-empty 'Match'es of a 'MatchGroup'.
    386 
    +-- See Note [Suppress warnings in PMC desugaring]
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     desugarMatches :: [Id] -> NonEmpty (LMatch GhcTc (LHsExpr GhcTc))
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                    -> DsM (PmMatchGroup Pre)
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    -desugarMatches vars matches =
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    +desugarMatches vars matches = discardWarningsDs $
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       PmMatchGroup <$> traverse (desugarMatch vars) matches
    389 391
    390 392 
     -- Desugar a single match
    ... ... @@ -398,8 +400,9 @@ desugarMatch vars (L match_loc (Match { m_pats = L _ pats, m_grhss = grhss })) =
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       -- tracePm "desugarMatch" (vcat [ppr pats, ppr pats', ppr grhss'])
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       return PmMatch { pm_pats = pats', pm_grhss = grhss' }
    400 402
    403 
    +-- See Note [Suppress warnings in PMC desugaring]
    401 404 
     desugarGRHSs :: SrcSpan -> SDoc -> GRHSs GhcTc (LHsExpr GhcTc) -> DsM (PmGRHSs Pre)
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    -desugarGRHSs match_loc pp_pats grhss = do
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    +desugarGRHSs match_loc pp_pats grhss = discardWarningsDs $ do
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       lcls <- desugarLocalBinds (grhssLocalBinds grhss)
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       grhss' <- traverse (desugarLGRHS match_loc pp_pats) (grhssGRHSs grhss)
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       return PmGRHSs { pgs_lcls = lcls, pgs_grhss = grhss' }
    ... ... @@ -593,6 +596,17 @@ The place to store the 'PmLet' guards for @where@ clauses (which are per
    593 596 
     'GRHSs') is as a field of 'PmGRHSs'. For plain @let@ guards as in the guards of
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     @x@, we can simply add them to the 'pg_grds' field of 'PmGRHS'.
    595 598
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    +Note [Suppress warnings in PMC desugaring]
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    +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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    +This module uses 'dsLExpr', 'dsExpr', and 'dsSyntaxExpr' to desugar
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    +expressions into Core for pattern match checking. The main desugaring
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    +pass in GHC.HsToCore processes these same expressions too, so without
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    +suppression any warnings would be emitted twice (#25996).
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    +
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    +To avoid this, the exported functions ('desugarPatBind', 'desugarMatches',
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    +'desugarGRHSs') are wrapped in 'discardWarningsDs', covering all internal
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    +desugarer calls without having to wrap each one individually.
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    +
    596 610 
     Note [Desugaring -XStrict matches in Pmc]
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     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    598 612 
     Consider (#21761)

  • testsuite/tests/deSugar/should_compile/T25996.hs
    1 
    +{-# OPTIONS_GHC -Wall #-}
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    +{-# OPTIONS_GHC -Wno-unused-local-binds #-}
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    +{-# OPTIONS_GHC -Wno-unused-top-binds #-}
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    +
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    +main :: IO ()
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    +main = do
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    +  pure ()
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    +  where
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    +    biz :: IO ()
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    +    biz = do
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    +      pure (10 :: Integer)
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    +      pure ()
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    +
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    +biz' :: IO ()
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    +biz' = do
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    +  pure (10 :: Integer)
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    +  pure ()

  • testsuite/tests/deSugar/should_compile/T25996.stderr
    1 
    +T25996.hs:11:7: warning: [GHC-81995] [-Wunused-do-bind (in -Wall)]
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    +    A do-notation statement discarded a result of type ‘Integer’
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    +    Suggested fix:
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    +      Suppress this warning by saying ‘_ <- pure (10 :: Integer)’
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    +
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    +T25996.hs:16:3: warning: [GHC-81995] [-Wunused-do-bind (in -Wall)]
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    +    A do-notation statement discarded a result of type ‘Integer’
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    +    Suggested fix:
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    +      Suppress this warning by saying ‘_ <- pure (10 :: Integer)’
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    +

  • testsuite/tests/deSugar/should_compile/all.T
    ... ... @@ -115,3 +115,4 @@ test('T19883', normal, compile, [''])
    115 115 
     test('T22719', normal, compile, ['-ddump-simpl -dsuppress-uniques -dno-typeable-binds'])
    116 116 
     test('T23550', normal, compile, [''])
    117 117 
     test('T24489', normal, compile, ['-O'])
    118 
    +test('T25996', normal, compile, [''])

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