Ben Gamari pushed to branch wip/T27456 at Glasgow Haskell Compiler / GHC

Commits:

• 42860214
  by Ben Gamari at 2026-06-29T11:12:36-04:00

  base: Display ExceptionContext in WhileHandling's textual description
  
  As originally-implemented the implementation for
  `WhileHandling(displayExceptionAnnotation)` would display the
  `ExceptionContext` of the exception which it carries (as this was the
  behavior of `displayException`, in terms of which
  `displayExceptionAnnotation` was implemented).
  
  However, in 284ffab3 the definition of `SomeException(displayException)`
  was changed to exclude the `ExceptionContext`. This means that
  `WhileHandling(displayExceptionAnnotation)` fails to describe the
  provenance of the exception which it captures, greatly limiting its
  utility.
  
  Return the implementation to its originally-specified behavior by
  implementing `WhileHandling(displayExceptionAnnotation)` in terms of
  `displayExceptionWithInfo`.
  
  Fixes #27456.
  

2 changed files:

• + changelog.d/T27456
• libraries/ghc-internal/src/GHC/Internal/Exception/Type.hs

Changes:

+section: base

+issues: #27456

+mrs: !

+synopsis:

+  Show `ExceptionContext` in `displayExceptionAnnotation` implementation of `WhileHandling`

+description:

+  In the past ``displayException`` (in terms of which ``WhileHandling``\'s ``displayExceptionAnnotation` is implemented) was changed to hide ``ExceptionContext``. This regressed the behavior of ``displayExceptionAnnotation`` from that which was originally specified. Restore the intended behavior of showing the ``ExceptionContext`` of the carried exception.

+

 instance ExceptionAnnotation WhileHandling where

   displayExceptionAnnotation (WhileHandling e) =

-    "While handling " ++ case lines $ displayException e of

+    "While handling " ++ case lines $ displayExceptionWithInfo e of

       [] -> ""

       (l1:ls) ->

         -- Indent lines forward.