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Sasha Bogicevic pushed to branch wip/27380 at Glasgow Haskell Compiler / GHC

Commits:

9c420942

by Sasha Bogicevic at 2026-07-19T21:37:28+02:00

parser: don't suggest ImportQualifiedPost when it is already enabled

-Wprepositive-qualified-module unconditionally attached a hint to
enable ImportQualifiedPost, even when the extension was already on
(as it is by default under GHC2021). Record the extension's state in
the PsWarnImportPreQualified diagnostic and drop the hint when it is
already enabled.

Fixes #27380

8 changed files:

+ changelog.d/27380
compiler/GHC/Parser/Errors/Ppr.hs
compiler/GHC/Parser/Errors/Types.hs
compiler/GHC/Parser/PostProcess.hs
+ testsuite/tests/module/T27380.hs
+ testsuite/tests/module/T27380.stderr
testsuite/tests/module/all.T
testsuite/tests/module/mod184.stderr

Changes:

changelog.d/27380

 +section: compiler
 +synopsis: Don't suggest enabling ``ImportQualifiedPost`` when it is already enabled.
 +  The :ghc-flag:`-Wprepositive-qualified-module` warning no longer suggests
 +  enabling the extension if it is already in effect (as it is by default
 +  under GHC2021).
 +issues: #27380
 +mrs: !16376

compiler/GHC/Parser/Errors/Ppr.hs

@@ -113,7 +113,7 @@ instance Diagnostic PsMessage where
                            <> if null prag then empty else text ":" <+> text prag
      PsWarnMisplacedPragma prag
        -> mkSimpleDecorated $ text "Misplaced" <+> pprFileHeaderPragmaType prag <+> text "pragma"
 -    PsWarnImportPreQualified
 +    PsWarnImportPreQualified _iqp_on
        -> mkSimpleDecorated $
              text "Found" <+> quotes (text "qualified")
               <+> text "in prepositive position"
@@ -603,7 +603,7 @@ instance Diagnostic PsMessage where
      PsWarnStarIsType                              -> WarningWithFlag Opt_WarnStarIsType
      PsWarnUnrecognisedPragma{}                    -> WarningWithFlag Opt_WarnUnrecognisedPragmas
      PsWarnMisplacedPragma{}                       -> WarningWithFlag Opt_WarnMisplacedPragmas
 -    PsWarnImportPreQualified                      -> WarningWithFlag Opt_WarnPrepositiveQualifiedModule
 +    PsWarnImportPreQualified{}                    -> WarningWithFlag Opt_WarnPrepositiveQualifiedModule
      PsWarnViewPatternSignatures{}                 -> WarningWithFlag Opt_WarnViewPatternSignatures
      PsErrLexer{}                                  -> ErrorWithoutFlag
      PsErrCmmLexer                                 -> ErrorWithoutFlag
@@ -735,8 +735,10 @@ instance Diagnostic PsMessage where
            then noHints
            else [SuggestCorrectPragmaName suggestions]
      PsWarnMisplacedPragma{}                       -> [SuggestPlacePragmaInHeader]
 -    PsWarnImportPreQualified                      -> [ SuggestQualifiedAfterModuleName
 -                                                     , suggestExtension LangExt.ImportQualifiedPost]
 +    PsWarnImportPreQualified iqp_on | iqp_on     -> [ SuggestQualifiedAfterModuleName ]
 +                                    | otherwise  -> [ SuggestQualifiedAfterModuleName
 +                                                    , suggestExtension LangExt.ImportQualifiedPost
 +                                                    ]
      PsWarnViewPatternSignatures{}                 -> [SuggestParenthesizePatternRHS]
      PsErrLexer{}                                  -> noHints
      PsErrCmmLexer                                 -> noHints

compiler/GHC/Parser/Errors/Types.hs

@@ -133,7 +133,7 @@ data PsMessage
     | PsWarnStarIsType
     -- | Pre qualified import with 'WarnPrepositiveQualifiedModule' enabled
 -   | PsWarnImportPreQualified
 +   | PsWarnImportPreQualified !Bool -- is 'ImportQualifiedPost' enabled?
     | PsWarnOperatorWhitespaceExtConflict !OperatorWhitespaceSymbol

compiler/GHC/Parser/PostProcess.hs

@@ -1327,7 +1327,7 @@ checkImportDecl mPre mPost preLevel postLevel = do
    -- Warn if 'qualified' found in prepositive position and
    -- 'Opt_WarnPrepositiveQualifiedModule' is enabled.
    whenJust mPre $ \pre ->
 -    warnPrepositiveQualifiedModule (tokenSpan pre)
 +    warnPrepositiveQualifiedModule (tokenSpan pre) importQualifiedPostEnabled
    return (qualSpec, levelSpec)
@@ -3499,9 +3499,9 @@ isImpExpQcWildcard _                  = False
  -----------------------------------------------------------------------------
  -- Warnings and failures
 -warnPrepositiveQualifiedModule :: SrcSpan -> P ()
 -warnPrepositiveQualifiedModule span =
 -  addPsMessage span PsWarnImportPreQualified
 +warnPrepositiveQualifiedModule :: SrcSpan -> Bool -> P ()
 +warnPrepositiveQualifiedModule span qualifiedPostEnabled =
 +  addPsMessage span $ PsWarnImportPreQualified qualifiedPostEnabled
  failNotEnabledImportQualifiedPost :: SrcSpan -> P ()
  failNotEnabledImportQualifiedPost loc =

testsuite/tests/module/T27380.hs

 +{-# LANGUAGE NoImportQualifiedPost #-}
 +{-# OPTIONS_GHC -Wprepositive-qualified-module #-}
 +-- Negative control for #27380: with the extension explicitly disabled,
 +-- the ImportQualifiedPost suggestion must still appear.
 +import qualified System.IO
 +main :: IO ()
 +main = System.IO.print "hi"

testsuite/tests/module/T27380.stderr

 +T27380.hs:5:8: warning: [GHC-07924] [-Wprepositive-qualified-module]
 +    Found ‘qualified’ in prepositive position
 +    Suggested fixes:
 +      • Place ‘qualified’ after the module name.
 +      • Perhaps you intended to use the ‘ImportQualifiedPost’ extension
++

testsuite/tests/module/all.T

@@ -295,3 +295,4 @@ test('T21826', normal, compile_fail, [''])
  test('T20007', normal, compile_fail, [''])
  test('T25901_imp_plain_wc', normal, compile_fail, [''])
  test('T25901_exp_plain_wc', normal, compile_fail, [''])
 +test('T27380', normal, compile, [''])

testsuite/tests/module/mod184.stderr

+-
  mod184.hs:6:8: warning: [GHC-07924] [-Wprepositive-qualified-module]
      Found ‘qualified’ in prepositive position
 -    Suggested fixes:
 -      • Place ‘qualified’ after the module name.
 -      • Perhaps you intended to use the ‘ImportQualifiedPost’ extension
 +    Suggested fix: Place ‘qualified’ after the module name.
++