sheaf pushed to branch wip/T27455 at Glasgow Haskell Compiler / GHC Commits: b8958d1e by Ben Gamari at 2026-07-03T13:50:19+02:00 base: Don't drop exception context in SomeException(toException) For reasons that are lost to time, the implementation of [CLC #200] that was merged inappropriately dropped `ExceptionContext` in the `toException` implementation given to `SomeException`. Fix this infelicity. [CLC #200]: https://github.com/haskell/core-libraries-committee/issues/200 - - - - - 4 changed files: - + changelog.d/T27455 - libraries/base/changelog.md - libraries/ghc-internal/src/GHC/Internal/Exception/Type.hs - testsuite/tests/ghc-e/should_run/ghc-e005.stderr Changes: ===================================== changelog.d/T27455 ===================================== @@ -0,0 +1,8 @@ +section: base +issues: #27455 +mrs: !16274 +synopsis: + Don't drop `ExceptionContext` in `SomeException(toException)` +description: + Previously the implementation of ``Exception(toException)`` given to `SomeException` would inappropriately drop the carried `ExceptionContext`. Now ``toException = id``, faithfully implementing the semantics proposed in :ref:`CLC Proposal #200 https://github.com/haskell/core-libraries-committee/issues/200`. + ===================================== libraries/base/changelog.md ===================================== @@ -33,6 +33,7 @@ * Evaluate backtraces for "error" exceptions at the moment they are thrown. ([CLC proposal #383](https://github.com/haskell/core-libraries-committee/issues/383)) * Hide implementation details when throwing exceptions in throw and throwSTM. ([CLC proposal #387](https://github.com/haskell/core-libraries-committee/issues/387)) * Change `hIsReadable` and `hIsWritable` such that they always throw a respective exception when encountering a closed or semi-closed handle, not just in the case of a file handle. ([CLC proposal #371](github.com/haskell/core-libraries-committee/issues/371)) + * The implementation of `toException` in `SomeException`'s `Exception` instance no longer drops exception context, in keeping with the behavior originally proposed in [CLC Proposal #200](https://github.com/haskell/core-libraries-committee/issues/200). * Annotate `onException` continuation with `WhileHandling`. ([CLC Proposal #397](https://github.com/haskell/core-libraries-committee/issues/397)) * Improve error message for `Data.Char.chr`. ([CLC Proposal #384](https://github.com/haskell/core-libraries-committee/issues/384)) ===================================== libraries/ghc-internal/src/GHC/Internal/Exception/Type.hs ===================================== @@ -55,7 +55,7 @@ import GHC.Internal.Data.Maybe import GHC.Internal.Data.Typeable (Typeable, TypeRep, cast) import qualified GHC.Internal.Data.Typeable as Typeable -- loop: GHC.Internal.Data.Typeable -> GHC.Internal.Err -> GHC.Internal.Exception -import GHC.Internal.Base (String, Void, fmap, return, ($), (.), (++)) +import GHC.Internal.Base (String, Void, fmap, return, ($), (.), (++), id) import GHC.Internal.Show import GHC.Internal.Types (Bool(..)) import GHC.Internal.Exception.Context @@ -231,13 +231,11 @@ class (Typeable e, Show e) => Exception e where -- | @since base-4.8.0.0 instance Exception Void --- | This drops any attached 'ExceptionContext'. +-- | NB: this instance preserves the attached 'ExceptionContext'. -- -- @since base-3.0 instance Exception SomeException where - toException (SomeException e) = - let ?exceptionContext = emptyExceptionContext - in SomeException e + toException = id fromException = Just backtraceDesired (SomeException e) = backtraceDesired e displayException (SomeException e) = displayException e ===================================== testsuite/tests/ghc-e/should_run/ghc-e005.stderr ===================================== @@ -4,3 +4,8 @@ foo HasCallStack backtrace: error, called at ghc-e005.hs:12:10 in main:Main + + +HasCallStack backtrace: + throwIO, called at ghc\GHCi\UI.hs:1655:31 in ghc-bin-10.1.20260629-inplace:GHCi.UI + View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b8958d1ec0cda9a4f7f1be9562aae252... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b8958d1ec0cda9a4f7f1be9562aae252... You're receiving this email because of your account on gitlab.haskell.org.