Simon Peyton Jones pushed to branch wip/T27731 at Glasgow Haskell Compiler / GHC

Commits:

• 192be0b6
  by Luite Stegeman at 2026-09-07T19:43:36-04:00

  rts: fix ctoi_tuple_spill_words getting out of sync
  
  Fix a few places that were not updating ctoi_tuple_spill_words
  correctly, leading to corruption/crashes when dealing with large
  unboxed tuples in bytecode:
  
   - captureContinuationAndAbort
   - findRetryFrameHelper/findAtomicallyFrameHelper
   - interpretBCO bci_BRK_FUN
  
  fixes #27633
  

• 604eb43c
  by Simon Jakobi at 2026-09-07T19:44:15-04:00

  Hadrian: don't capture the testsuite driver's output (#27780)
  
  a6061455d54 switched the Testsuite RunTest case from Shake's cmd to the
  cmd' wrapper. cmd' always captures stdout and stderr, and since the
  caller asks for Exit, it returns without dumping what it captured. As a
  result the testsuite output no longer appears in CI job logs: failures,
  performance metrics and the summary were lost with the job.
  
  Use cmdExe, the uncaptured cmd, as the other plain-cmd sites in that
  commit do.
  
  Fixes #27780.
  
  Assisted-by: Claude Fable 5.1
  

• 06eee015
  by Luite Stegeman at 2026-09-08T06:03:06+02:00

  rts: Fix missing memory barrier in eval_thunk_selector (#27477)
  
  unchain_thunk_selectors() was missing an ACQUIRE_LOAD for the
  indirectee, leading to segfaults and corruption during GC on
  weakly-ordered architectures.
  
  Fixes #27477
  

• f8b2bd8f
  by Alan Zimmerman at 2026-09-08T09:39:12-04:00

  EPA Fix HsCmdDo exact print with comments
  
  Exact printing of HsCmdDo was ignoring the location for the do
  statements, and this is an annotation that can have comments in it.
  
  Update it so we print the statements as a unit, including any
  comments.
  
  Also add the result of auditing that we capture comments in all needed
  places, noting that the remaining Anno SrcSpan instances are benign.
  

• 6b7dcb25
  by Simon Peyton Jones at 2026-09-09T10:14:38+01:00

  Simplify the error-suppression mechanism in GHC.Tc.Errors
  
  In GHC.Tc.Errors.reportWanteds we suppress some errors in favour of
  others.  But the mechanism had grown crufty, and #27331 exposed a bug.
  
  This MR makes it simpler and more uniform, by doing everything via
  the `ei_suppress` field of the ErrorItem.
  
  Claude then found another closely-related bug (see the review linked
  on !16564).  That bug is immortalised in new test T18851d.
  
  I'm still not happy with `ignoreConstraint` but we can worry about
  that another day; I have not touched it.
  

34 changed files:

• + changelog.d/T27731
• + changelog.d/fix-parallel-gc-selector-race-27477
• compiler/GHC/Hs/Doc.hs
• compiler/GHC/Hs/Extension/Pass.hs
• compiler/GHC/Tc/Errors.hs
• compiler/GHC/Tc/Errors/Types.hs
• compiler/GHC/Tc/Types/Constraint.hs
• hadrian/src/Builder.hs
• rts/Continuation.c
• rts/Interpreter.c
• rts/Schedule.c
• rts/sm/Evac.c
• + testsuite/tests/bytecode/T27633/Obj.hs
• + testsuite/tests/bytecode/T27633/T27633a.hs
• + testsuite/tests/bytecode/T27633/T27633a.stdout
• + testsuite/tests/bytecode/T27633/T27633b.hs
• + testsuite/tests/bytecode/T27633/T27633b.stdout
• + testsuite/tests/bytecode/T27633/all.T
• + testsuite/tests/ghci.debugger/scripts/T27633c.hs
• + testsuite/tests/ghci.debugger/scripts/T27633c.script
• + testsuite/tests/ghci.debugger/scripts/T27633c.stdout
• + testsuite/tests/ghci.debugger/scripts/T27633c_obj.hs
• testsuite/tests/ghci.debugger/scripts/all.T
• + testsuite/tests/rts/T27477.hs
• + testsuite/tests/rts/T27477.stdout
• testsuite/tests/rts/all.T
• testsuite/tests/typecheck/should_fail/FunDepOrigin1b.hs
• testsuite/tests/typecheck/should_fail/T18851.stderr
• + testsuite/tests/typecheck/should_fail/T18851e.hs
• + testsuite/tests/typecheck/should_fail/T18851e.stderr
• + testsuite/tests/typecheck/should_fail/T27731.hs
• + testsuite/tests/typecheck/should_fail/T27731.stderr
• testsuite/tests/typecheck/should_fail/all.T
• utils/check-exact/ExactPrint.hs

The diff was not included because it is too large.