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

Commits:

98c20394

by sheaf at 2026-06-10T05:11:09-04:00

Fix crash in Data.Data instance for HsCtxt

The Data.Data instance for HsCtxt contained an error for the 'toConstr'
method, which could trigger for example when looking at -ddump-tc-ast
traces. Replace it with the 'abstractConstr' pattern used in the rest of
the codebase.

2 changed files:

+ changelog.d/T27359
compiler/GHC/Hs/Instances.hs

Changes:

changelog.d/T27359

 +section: compiler
 +issues: #27359
 +mrs: !16142
 +synopsis:
 +  Fix ``Data.Data`` instance of ``HsCtxt`` to avoid a crash
 +description:
 +  The ``toConstr`` method of the ``Data.Data`` instance of ``HsCtxt`` now
 +  uses ``abstractConstr`` instead of ``error``, which avoids it triggering
 +  runtime crashes (e.g. when using ``-ddump-tc-ast``).

compiler/GHC/Hs/Instances.hs

@@ -46,6 +46,7 @@ import GHC.Hs.ImpExp
  import GHC.Parser.Annotation
  import GHC.Types.Name.Reader (WithUserRdr(..))
  import GHC.Types.InlinePragma (ActivationGhc)
 +import GHC.Utils.Misc (abstractConstr)
  import GHC.Data.BooleanFormula (BooleanFormula(..))
  import Language.Haskell.Syntax.Decls
  import Language.Haskell.Syntax.Decls.Foreign (CType(..), Header(..))
@@ -673,7 +674,7 @@ deriving instance Eq (IE GhcTc)
  instance Data HsCtxt where
    gunfold _ _ _ = error "no gunfold for HsCtxt"
    gfoldl _ k z = k z
 -  toConstr = error "no toConstr for HsCtxt"
 +  toConstr _ = abstractConstr "HsCtxt"
    dataTypeOf = error "no dataTypeOf for HsCtxt"
  deriving instance Data XXExprGhcRn