[Git][ghc/ghc][wip/exception-context-prereqs] base: Use displayException in top-level exception handler

[Ben Gamari (@bgamari)]

Ben Gamari pushed to branch wip/exception-context-prereqs at Glasgow Haskell Compiler / GHC


Commits:
57a5ca79 by Ben Gamari at 2024-02-19T14:42:24-05:00
base: Use displayException in top-level exception handler

Happily this also allows us to eliminate a special case for Deadlock
exceptions.

Implements [CLC #198](https://github.com/haskell/core-libraries-committee/issues/198).

- - - - -


3 changed files:

- libraries/base/changelog.md
- libraries/ghc-internal/src/GHC/Conc/Sync.hs
- libraries/ghc-internal/src/GHC/IO/Exception.hs


Changes:

=====================================
libraries/base/changelog.md
=====================================
@@ -2,6 +2,7 @@
 
 ## 4.20.0.0 *TBA*
   * Export `foldl'` from `Prelude` ([CLC proposal #167](https://github.com/haskell/core-libraries-committee/issues/167))
+  * The top-level handler for uncaught exceptions now displays the output of `displayException` rather than `show`  ([CLC proposal #198](https://github.com/haskell/core-libraries-committee/issues/198))
   * Add `permutations` and `permutations1` to `Data.List.NonEmpty` ([CLC proposal #68](https://github.com/haskell/core-libraries-committee/issues/68))
   * Add a `RULE` to `Prelude.lookup`, allowing it to participate in list fusion ([CLC proposal #175](https://github.com/haskell/core-libraries-committee/issues/175))
   * Implement `stimes` for `instance Semigroup (Endo a)` explicitly ([CLC proposal #4](https://github.com/haskell/core-libraries-committee/issues/4))


=====================================
libraries/ghc-internal/src/GHC/Conc/Sync.hs
=====================================
@@ -107,7 +107,6 @@ module GHC.Conc.Sync
 import Foreign
 import Foreign.C
 
-import Data.Typeable
 import Data.Maybe
 
 import GHC.Base
@@ -948,11 +947,9 @@ uncaughtExceptionHandler :: IORef (SomeException -> IO ())
 uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
    where
       defaultHandler :: SomeException -> IO ()
-      defaultHandler se@(SomeException ex) = do
+      defaultHandler se = do
          (hFlush stdout) `catchAny` (\ _ -> return ())
-         let msg = case cast ex of
-               Just Deadlock -> "no threads to run:  infinite loop or deadlock?"
-               _                  -> showsPrec 0 se ""
+         let msg = displayException se
          withCString "%s" $ \cfmt ->
           withCString msg $ \cmsg ->
             errorBelch cfmt cmsg


=====================================
libraries/ghc-internal/src/GHC/IO/Exception.hs
=====================================
@@ -105,7 +105,8 @@ blockedIndefinitelyOnSTM = toException BlockedIndefinitelyOnSTM
 data Deadlock = Deadlock
 
 -- | @since 4.1.0.0
-instance Exception Deadlock
+instance Exception Deadlock where
+    displayException _ = "no threads to run:  infinite loop or deadlock?"
 
 -- | @since 4.1.0.0
 instance Show Deadlock where



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/57a5ca79933a498e4089f031a2f119f54f64b6f6

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/57a5ca79933a498e4089f031a2f119f54f64b6f6
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