Matthew Pickering pushed to branch wip/t26751 at Glasgow Haskell Compiler / GHC Commits: 9ac926f9 by Matthew Pickering at 2026-01-08T16:01:01+00:00 Evaluate backtraces for "error" exceptions at the moment they are thrown See Note [Capturing the backtrace in throw] and Note [Hiding precise exception signature in throw] which explain the implementation. This commit makes `error` and `throw` behave the same with regard to backtraces. Previously, exceptiosn raised by `error` would not contain useful IPE backtraces. I did try and implement `error` in terms of `throw` but it started to involve putting diverging functions into hs-boot files, which seemed to risky if the compiler wouldn't be able to see if applying a function would diverge. Fixes #26751 - - - - - 1 changed file: - libraries/ghc-internal/src/GHC/Internal/Err.hs Changes: ===================================== libraries/ghc-internal/src/GHC/Internal/Err.hs ===================================== @@ -1,6 +1,7 @@ {-# LANGUAGE Trustworthy #-} {-# LANGUAGE NoImplicitPrelude, MagicHash, ImplicitParams #-} {-# LANGUAGE RankNTypes, PolyKinds, DataKinds #-} +{-# LANGUAGE BangPatterns #-} {-# OPTIONS_HADDOCK not-home #-} ----------------------------------------------------------------------------- @@ -25,6 +26,7 @@ module GHC.Internal.Err( absentErr, error, errorWithoutStackTrace, undefined ) where import GHC.Internal.Types (Char, RuntimeRep) import GHC.Internal.Stack.Types +import GHC.Internal.Magic import GHC.Internal.Prim import {-# SOURCE #-} GHC.Internal.Exception ( errorCallWithCallStackException @@ -33,7 +35,10 @@ import {-# SOURCE #-} GHC.Internal.Exception -- | 'error' stops execution and displays an error message. error :: forall (r :: RuntimeRep). forall (a :: TYPE r). HasCallStack => [Char] -> a -error s = raise# (errorCallWithCallStackException s ?callStack) +error s = + -- Evaluate SomeException before to get accurate callstacks (like throw) + let !se = noinline (errorCallWithCallStackException s ?callStack) + in raise# se -- Bleh, we should be using 'GHC.Internal.Stack.callStack' instead of -- '?callStack' here, but 'GHC.Internal.Stack.callStack' depends on -- 'GHC.Internal.Stack.popCallStack', which is partial and depends on @@ -73,7 +78,9 @@ undefined :: forall (r :: RuntimeRep). forall (a :: TYPE r). -- nor wanted (see #19886). We’d like to use withFrozenCallStack, but that -- is not available in this module yet, and making it so is hard. So let’s just -- use raise# directly. -undefined = raise# (errorCallWithCallStackException "Prelude.undefined" ?callStack) +undefined = + let !se = noinline (errorCallWithCallStackException "Prelude.undefined" ?callStack) + in raise# se -- | Used for compiler-generated error message; -- encoding saves bytes of string junk. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9ac926f9d6bc0bc33de0823be347fd6f... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9ac926f9d6bc0bc33de0823be347fd6f... You're receiving this email because of your account on gitlab.haskell.org.