GitLab

Simon Jakobi pushed to branch wip/sjakobi/T24813 at Glasgow Haskell Compiler / GHC

Commits:

9b714c4c

by Zubin Duggal at 2026-07-05T09:40:36+05:30

CorePrep: Don't speculatively evaluate bindings that we have already discovered to be absent

In #25924, we segfault because speculation forces a projection out of a RUBBISH dictionary
(which we generated because it absent).

Solution: Don't speculate on bindings we already know are absent.

Fixes 25924

4a59b3ee

by Zubin Duggal at 2026-07-05T09:40:36+05:30

Don't make absent fillers for terminating types

In #25924 we discovered that we could speculatively evaluate an absent filler
for a dictionary, and project a field (a superclass selector) out of it,
resulting in segfaults.

Solution: Never make an absent filler or rubbish literal for a terminating type
like a dictionary. mkAbsentFiller returns Nothing for isTerminatingType, so
worker/wrapper and the specialiser keep the real argument instead.

Some small metric decreases because we do a little less work in the
simplifier now.

Metric Decrease:
    T9872a
    T9872b
    T9872c
    TcPlugin_RewritePerf

383ddcd4

by Alan Zimmerman at 2026-07-06T07:08:16-04:00

EPA: Move the 'where' annotation for PatSynBind

This allows us to move it out of the MatchGroup exact print annotation
too

66d1a5d5

by fendor at 2026-07-07T16:57:56-04:00

Add 'backendInfoTableMapValidity' backend predicate

Check whether the backend supports the `-finfo-table-map` flag and
ignore it otherwise.

Improve by-design documentation of `backendCodeOutput`.

`Backend` is **abstract by design**. Make this clearer in
`backendCodeOutput` which is incorrectly being used as a proxy for
`Backend`.

Instead, define the desired property predicates in GHC.Driver.Backend
In the process, make `backendCodeOutput` total.

74f1071d

by fendor at 2026-07-07T16:57:56-04:00

Add failing test for `-finfo-table-map` and bytecode backend

If you compile a module using the bytecode backend, with
-finfo-table-map, then the info table map doesn't get populated for the
module.

This is because the -finfo-table-map code path is implemented mostly in
the StgToCmm phase which isn't run when creating bytecode.

Ticket #27039

28d63bca

by mangoiv at 2026-07-07T16:59:16-04:00

ci: don't fail nightly if there have been no changes that night

Fixes #27127

4ebfc478

by Rodrigo Mesquita at 2026-07-08T04:47:53-04:00

ttg: Using ShortText over FastString in the AST

To make the AST independent of GHC, this commit replaces usages of
`FastString` with `HText` in the AST, killing the last edge from
Language.Haskell.* to GHC.* modules.

Even though we /do/ want to use FastStrings in general -- critically in
Names or Ids -- there is no particular reason for the FastStrings that
occur in the AST proper to be FastStrings. Strings in the AST are
typically unique and don't benefit particularly from being interned
FastStrings with Uniques for fast comparison.

`HText` is a type synonym for `ShortText` which uses GHC's Modified
UTF-8 encoding exclusively.

Modified UTF-8 must be used to represent the Haskell AST because the
Haskell Report allows surrogate code points. `Data.Text.Text` functions
use Standard UTF-8 which replace surrogates with a placeholder value,
thus `Data.Text.Text` is unsuitable for AST strings. See the
`Language.Haskell.Syntax.Text` module header for more details.

Final progress towards #21592

Closes #21628

d910b353

by Simon Peyton Jones at 2026-07-08T04:48:36-04:00

Update equality-type documenation in GHC.Builtin.Types.Prim

Fix #27466

b2530542

by Simon Peyton Jones at 2026-07-08T04:48:36-04:00

Honour -dsuppress-coercions in GHC.Core.TyCo.pprCo

Fixes #27467

9a73179a

by Facundo Domínguez at 2026-07-08T04:49:26-04:00

Add item to MR checklist asking to squash fixup commits after approval

The checklist has an item that reads

    All commits are either individually buildable or squashed.

This item could be checked immediately after sending the merge request
though. If reviewers ask for amends later on, and the author amends
the merge request, there was no item that would remind the contributors
to squash the fixup commits before landing.

This commit adds a new item

    After all approvals and before landing: all fixup commits are squashed with their originating commits.

which should be harder to mark as done before approvals have been given.

ed09895d

by Andreas Klebinger at 2026-07-08T16:53:27-04:00

Fix a profiling race condition resulting in segfaults.

StgToCmm: Don't assume tagged FUN closures in closureCodeBody.
When entering a closure the self/node pointer might not be tagged in
some situations when a thunk is evaluated by multiple threads.
So we most AND away the tag bits rather than subtracting an expected tag.

Apply.cmm: Fix a race condition occuring when a thunk is mutated during GC.

In stg_ap_0_fast when might need to run GC before entering a thunk. If this happens
another thread or the GC itself might mutate the closure making entering it no longer
valid. We now check for this.

Add test and changelog for #27123 fixes.

67c03eb2

by Cheng Shao at 2026-07-08T16:54:09-04:00

ghc-heap: fix invalid srtlen returned by peekItbl when no-TNTC

This patch fixes the no-TNTC code path of `peekItbl` so that it looks
at the right memory address when reading the `srt` field from the
`StgInfoTable_` struct. Also adds a `T27465` regression test that
reproduces the bug on no-TNTC builds before the fix. Fixes #27465.

Co-authored-by: Codex <codex@openai.com>

2ecabb4f

by Zubin Duggal at 2026-07-09T09:23:25-04:00

hadrian: binary-dist-dir should not be the default target

Revert behaviour to pre 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2

In 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2, we applied the following behaviour change:

```
hadrian: Build stage 2 cross compilers
...
* hadrian: Make binary-dist-dir the default build target. This allows us
  to have the logic in one place about which libraries/stages to build
  with cross compilers. Fixes #24192
```

This is a major regression to development experience, a plain hadrian/build
--freeze1 now takes ages because we rebuild all docs (which need to go in the
binary dist dir).

`binary-dist-dir` is the wrong default target for regular GHC development work

Fixes #27445

e16388e3

by Zubin Duggal at 2026-07-09T09:23:25-04:00

.gitignore: Add the hadrian system.config introduced by commit 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2

Since

commit 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2
Author: Matthew Pickering <matthewtpickering@gmail.com>
Date:   Thu Dec 21 16:17:41 2023 +0000

    hadrian: Build stage 2 cross compilers

./configure produces /hadrian/cfg/system.config.{host,target}

Add these to .gitignore

7e8abf41

by Alan Zimmerman at 2026-07-09T09:24:12-04:00

EPA: Replace AnnListItem with simply [TrailingAnn]

Remove the unnecessary wrapper around a single field.

29032f17

by Zubin Duggal at 2026-07-09T09:24:58-04:00

testsuite: Keep real reason for fragile test failures

c34e03a7

by Zubin Duggal at 2026-07-09T09:24:58-04:00

testsuite: Fall back to the failure reason for empty JUnit bodies

409d40f0

by Zubin Duggal at 2026-07-09T09:24:58-04:00

testsuite: Show output diffs in JUnit output

Also refactor compare_outputs to return essentially a `Maybe Diff`
(`CompareOutput`) instead of a bool, but more pythonic. This
allows us to pass the diff through nice.

06fee1ab

by Zubin Duggal at 2026-07-09T09:24:58-04:00

perf notes: include stat deviation and acceptance window in notes so they show up in gitlab

57c0f32c

by mangoiv at 2026-07-10T11:08:38-04:00

driver: enable -finter-module-far-jumps by default

this fixes a compatibility bug with certain binutils/gcc versions where
we were seeing jump offset overflow errors.
This commit can probably reverted if we stop supporting the problematic
binutils/gcc verions (2.44 and 14.2, respectively)

Reolves #26994

4396a6f2
by Andrea Vezzosi at 2026-07-10T11:09:25-04:00
```
[Fix #27287] preserve ModBreaks in ModIface
```

ed261a7e

by Cheng Shao at 2026-07-14T17:59:38-04:00

hadrian: fix HLS support

This patch fixes hadrian's HLS support so one can rely on HLS when
working on the hadrian codebase. Fixes #27480.

Not building/linking shared libraries for hadrian is a severely
premature optimization; this top-level setting in `cabal.project` only
affects home packages while the dependencies in the cabal store are
built with vanilla/dynamic anyway, and even adding dynamic builds to
home packages would not be costly due to cabal's usage of
`-dynamic-too`.

eee8ec5b

by Cheng Shao at 2026-07-14T18:00:20-04:00

compiler: fix miscompiled %load_relaxed, add missing %store_relaxed

This patch fixes the %load_relaxed cmm primop compilation logic to
correctly use relaxed memory ordering, and adds the missing
%store_relaxed primop. Parsing logic of %load/%store with explicit
ordering is covered in the AtomicFetch test case. Fixes #27483.

Co-authored-by: Codex <codex@openai.com>

1718230f

by Alan Zimmerman at 2026-07-14T18:01:06-04:00

EPA: Keep binds and sigs together in HsValBindsLR

We combine them into a single list for GhcPs, wrapped in the
ValBind data type, which is the bind equivalent of ValD, having
constructors for binds and sigs.

This simplifies exact print processing, especially when using it to
update the contents of local binds, as we no longer need AnnSortKey
BindTag

6bd1ad2a

by Andreas Klebinger at 2026-07-14T18:01:49-04:00

Bump nofib submodule to account for MonoLocalBinds.

New versions of GHC enable MonoLocalBinds by default.
This breaks some of the benchmarks. I've fixed this and
this bump pulls in that fix.

7eb0f1c9

by Cheng Shao at 2026-07-14T18:02:31-04:00

testsuite: fix bytecodeIPE test under +ipe flavours

This patch fixes the bytecodeIPE test under +ipe flavours. It used to
fail under +ipe because the RTS is built with IPE info, then
stg_AP_info in RTS carries IPE info, so whereFrom wouldn't return
Nothing. Now the test checks IPE info of a datacon in the ghci-loaded
module which is not affected by whether the RTS is built with IPE info
or not. Fixes #27498.

Co-authored-by: Codex <codex@openai.com>

ef038aae

by cydparser at 2026-07-15T04:35:41-04:00

Reduce bytes allocated for `capabilities` in RTS (fixes #27487)

In rts/Capability.c, `capabilities` is an array of pointers, but it was allocated as if it were an
array of Capability's.

d377e83e

by Cheng Shao at 2026-07-15T04:36:27-04:00

rts: fix missing UNTAG in stg_readTVarIOzh

This patch fixes missing UNTAG on the current value closure read from
StgTVar. UNTAG is a no-op when it's stg_TREC_HEADER_info which is word
aligned; it may be a tagged closure, and reading info table from the
tagged address is an unaligned load which may cause issues on
platforms with strict alignment requirements.

Co-authored-by: Codex <codex@openai.com>

8ed03842

by Cheng Shao at 2026-07-15T04:36:27-04:00

rts: fix missing UNTAG in stg_control0zh_ll

This patch fixes missing UNTAG on the cont closure returned by
captureContinuationAndAbort. In case it's not NULL,
captureContinuationAndAbort returns a tagged StgContinuation closure,
in which case it must be untagged before accessing the
apply_mask_frame field.

In the past it worked out of luck: when apply_mask_frame was NULL then
mask_frame_offset is also 0 so the control flow didn't diverge to a
wrong path. Still, this is horribly wrong and will crash once
StgContinuation struct is refactored and fields are shuffled around.

Co-authored-by: Codex <codex@openai.com>

5aa7000a

by Cheng Shao at 2026-07-15T04:37:08-04:00

compiler: fix redundant AP thunk codegen when not using -ticky-ap-thunk

This patch fixes a double negation confusion in !7525 that results in
some redundant AP thunk code generation when not using
-ticky-ap-thunk. Now, we use `stgToCmmUseStdApThunk` to indicate
whether precomputed AP thunks in the RTS should be used, which
defaults to `True`, unless `-ticky-ap-thunk` is passed.
`-finfo-table-map` now also implies `-ticky-ap-thunk`, since when
doing IPE profiling we want the generated AP thunks to be unique.
Fixes #27502.

-------------------------
Metric Decrease:
    T3064
-------------------------

Co-authored-by: Codex <codex@openai.com>

d43a7b7a

by Brian McKenna at 2026-07-15T20:10:04+02:00

Strip ticks when desugaring bool guards

The special `considerAccessible` pattern was broken when compiling
with debug info. Compiling with debug info wraps expressions with
`SourceNote` ticks, which broke the internals of the
`desugarBoolGuard` function. Ticks are now ignored within this
function.

Fixes #27360

ede4b17b

by Ben Gamari at 2026-07-15T22:59:53-04:00

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.

0f64f348

by Cheng Shao at 2026-07-16T15:41:08+00:00

ci: add missing docker permission workaround in abi-test job

660cb239

by Cheng Shao at 2026-07-16T19:37:48+00:00

bindist: Fix make install -j race condition on macos/freebsd

This patch fixes make install -j race condition on macos/freebsd. BSD
install fails with EEXIST when multiple install processes concurrently
create the same prefix directory. So we add an `install_dirs`
prerequisite job that sequentially creates the directories for
subsequent jobs to work with. Fixes #27499.

Co-authored-by: Codex <codex@openai.com>

08130257

by Cheng Shao at 2026-07-16T19:37:48+00:00

ci: run bindist make install with -j

This patch makes the ci scripts run `make install` with `-j` to reduce
wall clock time when installing the bindist, see related issue for
benchmark numbers. This only affects ghc ci logic, the user-facing
default is up to distributors and is still `-j1`. Closes #27029.

d5ae6906

by Adam Gundry at 2026-07-17T04:57:43-04:00

Mark various language extension flags as deprecated (see #27329)

The following language extensions are now deprecated:

 - AlternativeLayoutRule
 - AlternativeLayoutRuleTransitional
 - ParallelArrays
 - PolymorphicComponents
 - Rank2Types

In addition, the warning `-Walternative-layout-rule-transitional`
has been marked as deprecated, as it is emitted only under the
deprecated extension `XAlternativeLayoutRuleTransitional`.

fe3b059c

by Andrew Lelechenko at 2026-07-17T04:58:26-04:00

base: re-export GHC.Environment.getFullArgs from System.Environment

CLC proposal https://github.com/haskell/core-libraries-committee/issues/431

722236dd

by sheaf at 2026-07-18T08:48:31-04:00

Coercion optimisation: avoid double-Sym for InstCo

Ticket #27374 pointed out an issue with GHC.Core.Coercion.Opt.optCoercion's
handling of InstCo: it contravened (LC2) in Note [The LiftingContext in optCoercion]
because it applied the ambient 'sym' to a coercion that was then added
to the lifting context substitution.

Fixes #27374

Co-authored-by: Simon Jakobi <simon.jakobi@gmail.com>

ff70fc75

by sheaf at 2026-07-18T08:48:31-04:00

Coercion optimisation: avoid exponential behaviour

The change to coercion optimisation of 'InstCo' in the previous commit
introduces exponential behaviour to the coercion optimiser. To avoid
this, this commit provides a way to push in 'Sym' of an already-optimised
coercion: GHC.Core.Coercion.Opt.mkDeepSymCo.

See Note [Pushing Sym without re-optimising] in GHC.Core.Coercion.Opt.

dfef27f0

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Move THREADED_RTS-conditional struct members to end of Capability

Accessing members of the Capability struct from CMM code rely on
accessor macros. (The macros are generated by deriveConstants).

These macros have a single definition. This means that the offsets of
all struct members must *not* vary based on THREADED_RTS vs
!THREADED_RTS. This requires that any struct members that are
conditional on THREADED_RTS must occur after the unconditional struct
members. Hence we move all the ones that are conditional on
THREADED_RTS to the end.

Add a deriveConstants entry for the iomgr member of the Capability
struct, which was the motivation for this change.

Add warning messages to help our future selves. Debugging this took me
a couple hours in gdb!

c254e022

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Make the IOManager API use CapIOManager rather than Capability

This makes the API somewhat more self-contained and more consistent.
Now the IOManager API and each of the backends takes just the I/O
manager structure. Previously we had a bit of a mixture, depending on
whether the function needed access to the Capability or just the
CapIOManager.

We still need access to the cap, so we introduce a back reference to
reach the capability, via iomgr->cap.

Convert all uses in select and poll backends, but not win32 ones.
Convert callers in the scheduler and elsewhere.

Also convert the three CMM primops that call IOManager APIs. They just
need to use Capability_iomgr(MyCapability()).

4f3d8f31

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Split posix/MIO.c out of posix/Signals.c

The MIO I/O manager was secretly living inside the Signals file.

Now it gets its own file, like any other self-respecting I/O manager.

52ce04a9

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Rationalise some scheduler run queue utilities

Move them all to the same place in the file.

Make some static that were used only internally.

Also remove a redundant assignment after calling truncateRunQueue that
is already done within truncateRunQueue.

75bbdebc

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Rename initIOManager{AfterFork} to {re}startIOManager

These are more accurate names, since these actions happen after
initialisation and are really about starting (or restarting) background
threads.

724c0517

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Free per-cap I/O managers during shutdown and forkProcess

Historically this was not strictly necessary. The select and win32
legacy I/O managers did not maintain any dynamically allocated
resources. The new poll one does (an auxillary table), and so this
should be freed.

After forkProcess, all threads get deleted. This includes threads
waiting on I/O or timers. So as of this patch, resetting the I/O
manager is just about tidying things up. For example, for the poll
I/O manager this will reset the size of the AIOP table (which
otherwise grows but never shrinks).

In future however the re-initialising will become neeecessary for
functionality, since some I/O managers will need to re-initialise
wakeup fds that are set CLOEXEC.

c007d122

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Add a TODO to the MIO I/O manager

The direction of travel is to make I/O managers per-capability and have
all their state live in the struct CapIOManager. The MIO I/O manager
however still has a number of global variables.

It's not obvious how handle these globals however.

b65ab7b3
by Duncan Coutts at 2026-07-18T08:49:12-04:00
```
Add a FIXME note in the Poll I/O manager
```

daf2bd6f

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Add missing updateRemembSetPushClosure in poll I/O manager

For the non-moving GC.

e33ca830

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Minor doc improvement to struct StgAsyncIOOp member outcome

Mention the enumeration names, as well as their numeric values. The rest
of the code uses the enum names.

4edd2579

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Minor doc improvements for StgTSOBlockInfo

Clarify that certain union members are used only by certain legacy
I/O managers. Hopefully we will be able to remove these at some point.

536bedbb

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Avoid exporting various win32-specific rts symbols

The BeginPrivate.h / EndPrivate.h scheme works perfectly well on
Windows, but all of the rts/win32/*.h files were not using it.

8139b5ac

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Remove wakeupIOManager, ioManagerWakeup and setIOManagerWakeupFd

We no longer need wakeupIOManager for the threaded RTS case, so we can
remove it and the bits only needed to support it. This includes the
pipe/eventfd fd shared between the RTS and the in-library I/O manager
used for waking up the I/O manager thread. The pipe/eventfd still
exists, but it no longer has to be communicated to the RTS, since the
RTS no longer needs to use it.

So we remove the RTS API export setIOManagerWakeupFd, and remove uses of
it within the I/O managers in ghc-internal.

74fe7c66

by Duncan Coutts at 2026-07-18T08:49:12-04:00

Add a new interruptIOManager API for the I/O managers

It will be used to interrupt awaitCompletedTimeoutsOrIO. Also update the
return type and docs for awaitCompletedTimeoutsOrIO to have it return
false when it gets interrupted, and have no useful post condition in
that case.

38792843

by Duncan Coutts at 2026-07-18T08:49:13-04:00

Add interruptIOManager support for select I/O manager

Uses the FdWakup mechanism.

2f3b00aa

by Duncan Coutts at 2026-07-18T08:49:13-04:00

Add interruptIOManager support for poll I/O manager

Uses the FdWakup mechanism.

A quirk we have to cope with is that we now need to poll one more fd --
the wakeup_fd_r -- but this fd has no corresponding entry in the
aiop_table. This is awkward since we have set up our aiop_poll_table to
be an auxilliary table with matching indicies.

The solution this patch uses (and described in the comments) is to have
two tables: struct pollfd *aiop_poll_table, *full_poll_table;
and to have the aiop_poll_table alias the tail of the full_poll_table.
The head entry in the full_poll_table is the extra fd. So we poll the
full_poll_table, while the aiop_poll_table still has matching indicies
with the aiop_table.

Hurrah for C aliasing rules.

cee50131

by Duncan Coutts at 2026-07-18T08:49:13-04:00

Add interruptIOManager support for win32 legacy I/O manager

And remove unused related helper resetAbandonRequestWait. It is not
called because the event is created in auto-reset mode, so never needs
to be reset manually.

cf453143

by Duncan Coutts at 2026-07-18T08:49:13-04:00

Note lack of interruptIOManager support for WinIO I/O manager

Though there's a plausible design, we can't sanely test it at the moment
due to related WinIO bugs. Filed as issue #27403.

1b74a0ad

by Duncan Coutts at 2026-07-18T08:49:13-04:00

Be more explicit about enum IOReadOrWrite values, and type within cmm

Belt and braces.

b388d093

by Brian McKenna at 2026-07-18T17:51:50-04:00

Ignore ticks in the pattern-match term oracle

The term-oracle in the pattern-match checker is keyed by a canonical
form of the scrutinee, computed by `makeDictsCoherent`. That canonical
form was tick-sensitive: two occurrences of an otherwise identical
expression that happened to carry different ticks were treated as
distinct values, breaking long-distance information.

This shows up in practice under `-finfo-table-map`, because the
desugarer wraps every record-selector use site in a `SourceNote`
carrying that site's span. For example:

     data Box = Box { unBox :: Maybe Int }
     f b = case unBox b of
       Nothing -> 0
       Just _  -> let Just x = unBox b in x

The two `unBox b` expressionss carry different SourceNote spans, the
pattern-match checker sees them as different, the long-distance
information from the outer `Just _` branch never reaches the
let-pattern, and `Just x = unBox b` is wrongly reported as
non-exhaustive.

We now strip all ticks in `makeDictsCoherent`.  This is documented as
Wrinkle (UD1) of Note [Unique dictionaries in the TmOracle CoreMap].

Fixes #27314

c23e1acb

by Mrjtjmn at 2026-07-18T17:52:45-04:00

Add explanations for unsolved Typeable constraints

This commit adds explanations for unsolved 'Typeable' constraints.

GHC will now provide additional explanations for an unsolved constraint
of the form 'Typeable ty', explain why GHC did not solve Typeable constraint.
e.g.:
 - 'ty' is a polymorphic type (e.g. forall a. a -> a)
 - 'ty' is a qualified type (e.g. Eq Int => Int)
 - 'ty' is an unboxed sum type
 - 'ty' is an unreduced type family application
 - 'ty' whose kind is not typeable

Fixes #26532

cbef021e
by Artem Pelenitsyn at 2026-07-19T07:49:55-04:00
```
ghc-internal: Lock.hs: fix typo and indentation
```

42918646

by Duncan Coutts at 2026-07-19T07:50:36-04:00

Fix failing test GcStaticPointers for non-moving GC

Minor mistake in asserting something before checking for that same
thing.

Specifically, Bdescr asserts HEAP_ALLOCED_GC, but Bdescr was being used
prior to a guard that checks HEAP_ALLOCED_GC. The solution is just to
move the use of Bdescr after the guard.

Thanks to Simon Jakobi for identifying the problem.

c2f6dcd4

by Sasha Bogicevic at 2026-07-20T10:31:56+02:00

Improve error messages for invalid record wildcards

Record wildcard hints are now shown in more contexts and include
constructor arity; matching with `..` on a fieldless constructor
now produces a dedicated error message.

Fixes #21101

4c02e76b

by Duncan Coutts at 2026-07-21T10:37:21-04:00

Mark test T27105 as fragile, citing issue #27522

Scheduler fairness is fine, except when it isn't. And it isn't on CI
machines surprisingly often! See the issue for details.

43dd2b15

by Recursion Ninja at 2026-07-21T17:09:53-04:00

Resolving many TTG related orphan type-class instances

This is part a technical debt removal effort made possible now
that separating out the AST via TTG has come to a close.

As the AST in 'L.H.S' has been incrementally separated from the GHC internals,
there are many accumulated orphan instance of 'Binary', 'NFData', 'Outputable',
and 'Uniquable'. The orphan instance of data-types from within 'L.H.S' have had
their orphan instances moved to either:
  1. The module which defines the data-type
  2. The module which defines the type-class;
     i.e. moving an orphan 'Binary' instance to 'GHC.Utils.Binary'

Orphan instances resolved (37):

  | Data-type            | Resolved instance(s)       | Former orphan module(s)   |
  | -------------------- | -------------------------- | ------------------------- |
  | Role                 | Binary, NFData, Outputable | GHC.Core.Coercion.Axiom   |
  | SrcStrictness        | Binary, NFData, Outputable | GHC.Core.DataCon          |
  | SrcUnpackedness      | Binary, NFData, Outputable | GHC.Core.DataCon          |
  | Fixity               | Binary, Outputable         | GHC.Hs.Basic              |
  | FixityDirection      | Binary, Outputable         | GHC.Hs.Basic              |
  | LexicalFixity        | Outputable                 | GHC.Hs.Basic              |
  | CCallTarget          | NFData                     | GHC.Hs.Decls.Foreign      |
  | CType                | NFData                     | GHC.Hs.Decls.Foreign      |
  | Header               | NFData                     | GHC.Hs.Decls.Foreign      |
  | OverlapMode          | Binary, NFData             | GHC.Hs.Decls.Overlap      |
  | WithHsDocIdentifiers | NFData, Outputable         | GHC.Hs.Doc                |
  | HsDocString          | NFData                     | GHC.Hs.DocString          |
  | HsDocStringChunk     | Binary, Outputable         | GHC.Hs.DocString          |
  | HsDocStringDecorator | Binary, Outputable         | GHC.Hs.DocString          |
  | NamespaceSpecifier   | Outputable                 | GHC.Hs.ImpExp             |
  | ForAllTyFlag         | Binary, NFData, Outputable | GHC.Hs.Specificity        |
  | Specificity          | Binary, NFData             | GHC.Hs.Specificity        |
  | PromotionFlag        | Binary, Outputable         | GHC.Types.Basic           |
  | FieldLabelString     | Outputable, Uniquable      | GHC.Types.FieldLabel      |
  | InlinePragma         | Binary                     | GHC.Types.InlinePragma    |

-------------------------
Metric Decrease:
    hard_hole_fits
-------------------------

Closes #21262, #27469

ab9ab895

by Cheng Shao at 2026-07-21T17:10:53-04:00

rts: always use StgInt to represent cost center id

Currently cost center id is modeled as `Int` and it should be `StgInt`
uniformly in the RTS, hence this patch. Fixes #27524.

94d8f83b

by Cheng Shao at 2026-07-22T11:30:40-04:00

hadrian: clean up stale cabal package flags in the tree

This patch cleans up stale cabal package flags in the tree and related
hadrian/autoconf logic. Closes #27474.

Co-authored-by: Codex <codex@openai.com>

0bf1d8c9

by Sasha Bogicevic at 2026-07-22T11:31:21-04:00

parser: don't suggest ImportQualifiedPost when it is already enabled

-Wprepositive-qualified-module unconditionally attached a hint to
enable ImportQualifiedPost, even when the extension was already on
(as it is by default under GHC2021). Record the extension's state in
the PsWarnImportPreQualified diagnostic and drop the hint when it is
already enabled.

Fixes #27380

700a1dd1

by Simon Jakobi at 2026-07-23T11:21:20-04:00

ci: Reduce lint job setup costs

Avoid fetching unnecessary history and submodules for lightweight lint
jobs. Run changelog validation without Hadrian.

Because the lint-author job is now based on the .lint template directly,
we enhance it to allow Git to read from the runner-owned checkouts,
In the previously used .lint-params template, this permissions issue was
addressed via `chown`.

Closes #27521.

Assisted-by: gpt-5.6-sol via Codex CLI

26a44fb0

by ARATA Mizuki at 2026-07-23T11:22:10-04:00

testsuite: Fix memory issues of doublex2_* and simd010

doublex2_* had reads from uninitialized memory.

simd010 had out-of-bounds array access.

Fixes #27544

4d798b17