GitLab

Cheng Shao pushed to branch wip/terrorjack/asan at Glasgow Haskell Compiler / GHC

Commits:

72c8de5c

by Simon Jakobi at 2026-05-23T18:41:42-04:00

Implement List.elem via foldr

...in order to allow specialization to Eq instances.

The implementation of notElem is updated for consistency.`

Corresponding CLC proposal:
https://github.com/haskell/core-libraries-committee/issues/412

Addresses #27096.

3268c610

by Alan Zimmerman at 2026-05-23T18:42:30-04:00

EPA: Fix span for qualified multiline string

Fix the span for a qualified multiline string like

  Text."""
    I'm a multiline
    Text value
    !
  """

to extend to the end of the entire string, not just the first line.

Closes #27274

1f096790

by Alan Zimmerman at 2026-05-23T18:43:20-04:00

EPA: Fix exact printing namespace-specified wildcards

Ensures correct printing of imports of the form

   import Data.Bool (data True(data ..))
   import Data.Bool (data True(type ..))

Closes #27291

56ada7c0

by Mrjtjmn at 2026-05-23T18:44:19-04:00

Fix ambiguous syntax of BangPatterns in users guide

Update documentation for the BangPatterns extension to specify
how surrounding whitespace affects interpretation of `!`.

* Only when there is whitespace before `!` and no whitespace after,
  it is recognized as a BangPattern.
* Other cases `⟨varid⟩!⟨varid⟩`, `⟨varid⟩ ! ⟨varid⟩`, `⟨varid⟩! ⟨varid⟩`
  are treated as infix operators.

579aa0b7

by Simon Jakobi at 2026-05-25T16:31:26-04:00

Ensure that SetOps.{minusList,unionListsOrd} can be specialized

...by marking them INLINABLE. Haddock allocates 0.1–0.3% less as a
result.

This also removes some redundant constraints on unionListsOrd.

cccf45da

by Cheng Shao at 2026-05-25T16:32:13-04:00

wasm: ensure post-linker output is synchronous ESM

This patch fixes wasm backend's post-linker output script to ensure
it's synchronous ESM and doesn't use top-level await, which doesn't
work in ServiceWorkers. Fixes #27257.

8db331a3

by Zubin Duggal at 2026-05-26T04:54:03-04:00

Update to semaphore-compat 2.0.0 using v2 of the protocol

On Linux and other POSIX platforms, GHC's -jsem jobserver client now
speaks v2 of the semaphore-compat protocol, which uses Unix domain
sockets in place of POSIX named semaphores. This avoids the libc-ABI
issues that affected the old implementation. Windows is unaffected
and continues to use the v1 protocol (Win32 named semaphores); its
reported protocol version remains v1.

When GHC receives a -jsem name whose protocol version it does not
support, it emits a -Wsemaphore-version-mismatch warning and falls
back to -j<N> rather than crashing. ghc --info exposes the supported
version in a new "Semaphore version" entry so cabal-install can detect
a mismatch before invoking GHC.

Users on a cabal-install that predates the v2 update will continue to
build successfully on Linux/POSIX, but will lose the cross-process
-jsem coordination and fall back to -j<N> per GHC invocation. Users
must upgrade to a cabal-install that supports protocol v2 to recover
full parallelism.

Also fix a leak in cleanupSem (#27253): cleanupSem used to snapshot
heldTokens and release them before killing the loop, while the loop's
in-flight acquire/release children could still be mutating it.
Cleanup now runs inside the loop's own exit handler, after draining
the active child via a new activeChild TVar, so the snapshot has no
concurrent mutator.

See also:
- GHC proposal amendment: https://github.com/ghc-proposals/ghc-proposals/pull/673
- cabal-install patch: https://github.com/haskell/cabal/pull/11628
- semaphore-compat MR: https://gitlab.haskell.org/ghc/semaphore-compat/-/merge_requests/8

Bump semaphore-compat submodule to 2.0.0

Fixes #25087 and #27253

17be4f1f

by Alan Zimmerman at 2026-05-26T04:54:52-04:00

EPA: Record semicolons in HsModifier

Ensure the semi colons are captured in the ParsedSource for code like

  %True;; %False;
  instance C D

It makes HsModifier (and hence HsModifierOf) LocatedA, so the semi
colons can be recorded as [TrailingAnn]

Also rename pprHsModifiers to pprLHsModifiers to match.

Closes #27294

8f991755

by fendor at 2026-05-26T11:02:52-04:00

Revert prog003 acceptance

We thought the commit 286f1adff3e78d775ff325caff71d0cee25d710b fixed the
test, but due to changes to ghci, modules loaded during the GHCi
session, the test was actually no longer testing what it set out to do,
"fixing" the broken test.

As modules are added to the `interactive-session` home unit, the object code needs
to be compiled with `-this-unit-id interactive-session`, otherwise the
object code won't be used.
Once this has been fixed in the test, the test fails as expected again.

277a3687

by mangoiv at 2026-05-26T11:03:40-04:00

libraries/process: bump submodule to v1.6.29.0

This submodule bump resolves a segfault on macos 15.
Fixes #27144

6779bb0c

by mangoiv at 2026-05-26T11:03:40-04:00

libraries/unix: in submodule, don't pick branch 2.7

The 2.7 branch is outdated and the module has been advanced far beyond
it anyway, so remove that line.

4a645683

by Simon Peyton Jones at 2026-05-27T21:41:59-04:00

Trim the continuation in mkDupableContWithDmds

When there are no remaining argument demands, it means the application
is bottoming. In this case, we can trim the continuation to avoid the
panic that was observed in #27261.

See Note [Trimming the continuation for bottoming functions] in
GHC.Core.Opt.Simplify.Iteration.

8ab506ff

by Cheng Shao at 2026-05-27T21:42:47-04:00

ghci: fix module name string lifetime in hs_hpc_module invocation

This patch makes hpcAddModule pass a properly malloced module name
string to hs_hpc_module, instead of using useAsCString which causes
use-after-free of module name string. Fixes #27297.

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

b0233814

by sheaf at 2026-05-27T21:43:31-04:00

Relax acceptance threshold for T10421

As seen in #27289, the 1% acceptance threshold for this text was
overly narrow, resulting in spurious test failures. This commit widens
the acceptance threshold to 2%. Fixes #27289.

63ce5770

by Luite Stegeman at 2026-05-28T12:23:35-04:00

Fixes for black holes

 - suspend duplicate work for eager black holes
 - detect eager black holes in checkBlockingQueues
 - don't overwrite existing black holes even if they're not
     in an eager blackhole frame
 - don't deadlock on self when thunk is already blackholed

Fixes #26936

037a80dc

by Tom McLaughlin at 2026-05-28T12:24:36-04:00

Event/Windows.hsc: rethrow exceptions in overlapped IO

This prevents the WinIO manager from swallowing exceptions in overlapped IO. It
was added to make WinIO support possible in the `network` library. See
https://gitlab.haskell.org/ghc/ghc/-/issues/27283.

We also bump __IO_MANAGER_WINIO__ to 2 so libraries can gate on this using CPP.

2d53bcdb

by Wolfgang Jeltsch at 2026-05-28T12:25:21-04:00

Allow `downsweep` to use nodes of an existing module graph

To this end, `downsweep` has not been able to use the nodes of a module
graph obtained from a previous downsweeping round. In some GHC API
applications, downsweeping is performed somewhat incrementally and
therefore could profit from reusing such existing results. This
contribution makes this possible.

Resolves #27054.

Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>

f4fbb583
by Simon Jakobi at 2026-05-28T12:26:04-04:00
```
Add regression test for T11226

Closes #11226.
```

ed29a5e6

by Sven Tennie at 2026-05-28T17:30:36-04:00

Add optional config setting for LibDir (#19174)

Previously, the `libDir` was derived from `topDir`. This won't work for
inplace stage2 cross-compilers where binaries and libraries are in
different stage dirs (`_build/stage1/` for executables and
`_build/stage2` for libraries).

`LibDir` is set in the inplace `settings` files. For bindists, we
generate a new `settings` file with no `LibDir` entry. GHC then defaults
to use `topDir` as `libDir` again. This keeps the bindist relocatable.

If `LibDir` is a relative path, it is interpreted relatively to
`topDir`.

The global package db is part of the `lib/` folder. If we want to point
for inplace cross-compilers to the succeeding stage's folder, this is
done by setting `LibDir`. Thus, the global package db must be found
relative to `libDir`` (which may default to `topDir` or be set by
`LibDir`).

The complexity of settings becomes scary. So, add a test to ensure
`LibDir` works as expected.

8339cf8f

by Sven Tennie at 2026-05-28T17:30:36-04:00

Add Haddock to FileSettings

Helping to understand the fields' meanings without deeper analyses.

4ce251e4

by Sylvain Henry at 2026-05-28T17:31:39-04:00

foundation test: skip signed minBound `quot` (-1) (#27222)

`minBound `quot` (-1)` for fixed-width signed integers is platform
dependent: the mathematical result -minBound is not representable in
the type. On x86, IDIV traps; LLVM's sdiv is undefined behaviour in
this case; on AArch64/RISC-V, SDIV wraps to minBound.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

b8ba7e61

by Simon Jakobi at 2026-05-28T17:32:23-04:00

Prevent dictionary-passing in checkTyEqRhs

...by pre-specializing it to TcM.

Previously, wherever checkTyEqRhs was used in other modules, the
Core showed dictionary passing ($fMonadIOEnv). The added SPECIALIZE
pragma prevents this.

d603477f

by David Eichmann at 2026-05-29T13:17:12-04:00

Hadrian: create a ghc-internal .def file per ghc-internal dll

The .def file generated from rts/win32/libHSghc-internal.def.in contains
the name of the ghc-internal dll. The correct dll name differs based
on if the dll is inplace/final and if using the Dynamic way. Previously,
this was not accounted for and inconsistent dlls names where used. That
led to failure when loading dlls at runtime in experiments with windows
dynamic linking.

1fc21753

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: copy backend interface haddocks to Native backend (#27305)

The haddock comments documenting the BigNat backend interface (function
contracts, expected MutableWordArray# sizes, return-value semantics, etc.)
were attached to the FFI backend module. Copy them to the Native backend
so they remain in tree once the FFI backend is removed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

717059df

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: remove FFI backend (#27305)

The FFI backend of ghc-bignum (now part of ghc-internal) had no known
users and is easy to recreate by relinking ghc-internal with a custom
backend. Remove the backend module, the bignum-ffi cabal flag, and the
ffi option from Hadrian's --bignum selector. The backend interface
documentation now lives in the Native backend module.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

4bb3b1d8

by Sylvain Henry at 2026-05-29T13:18:14-04:00

ghc-bignum: remove Check backend (#27305)

The Check backend of ghc-bignum (now part of ghc-internal) compared the
selected backend's output against the Native backend for validation.
It had no known users. Remove the backend module, the bignum-check
cabal flag, the bignumCheck Hadrian flavour field, and the check-
prefix in Hadrian's --bignum selector.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

6b3044a0
by David Eichmann at 2026-05-30T11:58:48-04:00
```
Add code comments to allocator code
```

f4e04210

by Matthew Pickering at 2026-05-30T11:59:34-04:00

hadrian: Refactor system-cxx-std-lib rules

I noticed a few things wrong with the hadrian rules for
`system-cxx-std-lib` rules.

* For `text` there is an ad-hoc check to depend on `system-cxx-std-lib`
outside of `configurePackage`.
* The `system-cxx-std-lib` dependency is not read from cabal files.
* Recache is not called on the packge database after the `.conf` file is
generated, a more natural place for this rule is `registerRules`.

Treating this uniformly like other packages is complicated by it not
having any source code or a cabal file. However we can do a bit better
by reporting the dependency firstly in `PackageData` and then needing
the `.conf` file in the same place as every other package in
`configurePackage`.

This commit increases the `shakeVersion`, to provide backwards
compatibility to previous builds with different PackageData.

Fixes #25303

Co-authored-by: Sven Tennie <sven.tennie@gmail.com>

576987d0

by Simon Jakobi at 2026-06-02T04:53:36-04:00

compiler: use nubOrd from containers

Address #27103 by replacing GHC.Utils.Misc.ordNub[On] with
Data.Containers.ListUtils.nubOrd[On].

Note that nubOrd suffers from a small inefficiency, a fix for which
will be included in the next containers release:

  https://github.com/haskell/containers/issues/1202

deea53c3

by David Eichmann at 2026-06-02T04:54:22-04:00

Hadrian: disable response files for GHC/Haddock builders on non-Windows

This makes debugging build errors easier on non-windows hosts.
See issue #27230

f2f5c6ba
by Nikita Efremov at 2026-06-02T16:04:54+00:00
```
fix typo : compete with performance, not complete
```

5524ea0e

by Wolfgang Jeltsch at 2026-06-03T08:01:26-04:00

Make the current `base` buildable with GHC 9.14

This comprises the following changes:

  * Disable some imports into `GHC.Base` for GHC 9.14
  * Disable some imports into `Prelude` for GHC 9.14
  * Disable separate `ArrowLoop` import for GHC 9.14
  * Disable `GHC.Internal.STM` import for GHC 9.14
  * Disable `GHC.Internal.Unicode.Version` import for GHC 9.14
  * Disable `GHC.Internal.TH.Monad` import for GHC 9.14
  * Add alternative `fixIO` import for GHC 9.14
  * Add alternative `unsafeCodeCoerce` import for GHC 9.14
  * Disable hiding of imported SIMD operations for GHC 9.14
  * Disable use of GHC 9.14’s `printToHandleFinalizerExceptionHandler`
  * Enable use of `getFileHash` from `ghc-internal` for GHC 9.14
  * Make `thenA` available for GHC 9.14
  * Make `thenM` available for GHC 9.14
  * Disable translation of `IoManagerFlagPoll` for GHC 9.14
  * Add `hGetNewlineMode` for GHC 9.14

d3438055
by Enrico Maria De Angelis at 2026-06-03T08:02:17-04:00
```
Fix #27067 - Clarify haddocks on `minusNaturalMaybe`
```

f9bcfac2

by sheaf at 2026-06-03T14:47:19-04:00

Avoid mkTick in Core Prep breaking ANF

As discovered in #27182, mkTick can break ANF. This patch introduces a
variant of mkTick that skips the single optimisation that could break
ANF. This is preferrable over switching to the raw Tick constructor,
as the latter may introduce spurious cost centres in profiling reports.

This is a temporary measure until we more thoroughly refactor how
mkTick works (see #27141).

See Note [mkTick breaks ANF] in GHC.CoreToStg.Prep.

Fixes #27182

cf1fd661

by Artem Pelenitsyn at 2026-06-03T14:48:09-04:00

clarify comment for getSizeofMutableByteArray#: we get the size in bytes, not "elements"

a3b431f3

by David Eichmann at 2026-06-04T10:10:19+00:00

Hadrian: convert env variable ACLOCAL_PATH to unix paths.

Convert ACLOCAL_PATH to a unix style path when invoking autoreconf.
Autoreconf doesn't handle windows paths.
See Note [Autoreconf unix paths from ACLOCAL_PATH].

Fixes #27311

18f6138a

by Simon Jakobi at 2026-06-04T20:20:31-04:00

testsuite: Deduplicate --only test names

config.only is assumed to be a set, but supplying --only overwrote it
with the (list) argparse result, which can contain duplicates. When a
test ran, config.only.remove(name) dropped only the first occurrence,
so a duplicated name lingered and was later misreported as a
"test not found" framework failure. Store it as a set instead.

Fixes #27322

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

2f3cc9ff

by Simon Jakobi at 2026-06-08T07:55:49-04:00

testsuite: detect fast bignum via ghc-internal, not removed ghc-bignum

The ghc-bignum package was merged into ghc-internal, so the BIGNUM_GMP
probe in test.mk ran `ghc-pkg field ghc-bignum exposed-modules`, which
fails with "cannot find package ghc-bignum". That error went to stderr
and leaked into the captured stderr of every makefile_test, causing
spurious [bad stderr] failures across the suite. The probe also silently
returned empty, so config.have_fast_bignum was wrongly False even on GMP
builds.

Probe ghc-internal's extra-libraries for the gmp library instead: the
GMP backend module is an other-module (not exposed), but GMP_LIBS adds
gmp to extra-libraries only on a GMP build, so this distinguishes the
backends. Redirect stderr to keep any future missing-package error off
the harness's stderr.

This also removes a stale comment as per suggestion from hsyl20.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

eb3bf6e7

by Alan Zimmerman at 2026-06-08T07:56:32-04:00

EPA: Rename Transform.anchorEof to addModuleCommentOrigDeltas

This now matches what it actually does.

498bb21a

by David Eichmann at 2026-06-09T18:02:39-04:00

Hadrian: avoid response files when command line is short enough

This replaces the logic of always using response files on Windows.
With the new condition based on command line lenght, reponse files
can be avoided in many more cases (on windows).

Now that response files are only used in a small number of cases,
response files are always kept and the -r / --keep-response-files
command line options have been removed

The response file paths are nolonger randomized. They are placed in the
`_build/rsp` directory. This ensures they are ignored by git and we
that Hadrian reuses response file paths when rebuilding rather than
leaving stale response files around.

Update user guide putting response files in its own section

87f510a5
by Simon Hengel at 2026-06-09T18:03:25-04:00
```
Don't use non-breaking spaces
```

41a19379

by David Eichmann at 2026-06-09T18:04:11-04:00

Hadrian: remove unused wrapper scripts from windows bindist

These wrapper scripts are only installed on non-relocatable builds
which are not generally supported on windows.

ce01ccb6

by sheaf at 2026-06-10T05:08:48-04:00

Don't drop ticks around variables of type `IO ()`

GHC.Core.Utils.mkTick is responsible for placing a tick on a Core
expression. It contains logic for dropping SCCs (non-counting profiling
ticks) around non-function variables, as such variables cannot
meaningfully contribute to profiles. However, the logic for what counts
as a function was incorrect: it used `isFunTy` which returns 'False' for
types such as 'IO ()' where the function arrow is hidden under a
newtype.

We now use 'mightBeFunTy' instead of 'isFunTy'. This ensures we don't
drop ticks in cases we aren't sure.

On the way, we improve the documentation of 'isFunTy', 'isPiTy' and
'mightBeFunTy', and update the latter's implementation to consistently
handle unary classes.

Fixes #27225

-------------------------
Metric Decrease:
    T5642
-------------------------

d311c4f1

by Simon Jakobi at 2026-06-10T05:09:32-04:00

testsuite: Add regression test for #4081

Check that a strict constructor field is unboxed once outside an
enclosing loop, not re-inspected each iteration (the float-out
case-floating from 9cb20b488). Uses simonpj's `data T a = T !a` example
from the ticket; T4081.stderr captures the expected Core.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

333df444

by sheaf at 2026-06-10T05:10:25-04:00

Check for cabal-install >= 3.12 upfront

Starting with commit 8cb99552f607f6bc4000e45ab32532d50c8bb996, Hadrian
requires cabal-install >= 3.12 in order to use the 'cabal path' command
that was introduced in version 3.12, as per
  https://github.com/haskell/cabal/blob/a51c4ee1556d816ad86e90db7e6330dd51b0b6e7/release-notes/cabal-install-3.12.1.0.md?plain=1#L45

This was not reflected in the Hadrian build script, causing a delayed
build failure instead of enforcing the version requirement upfront,
which this patch does.

Fixes #27317

98c20394

by sheaf at 2026-06-10T05:11:09-04:00

Fix crash in Data.Data instance for HsCtxt

The Data.Data instance for HsCtxt contained an error for the 'toConstr'
method, which could trigger for example when looking at -ddump-tc-ast
traces. Replace it with the 'abstractConstr' pattern used in the rest of
the codebase.

5ac9ce7d

by Zubin Duggal at 2026-06-10T21:26:32+05:30

hadrian: Remove old package.conf files when generating new ones

Old package.conf files might exists with different hashes, causing issues like #26661

Fixes #26661

c9015f09

by sheaf at 2026-06-11T12:40:28-04:00

Fix AArch64 clobbering bug for MUL2

On AArch64, the code generator could clobber one of the input operands
when computing the lower bits of a MUL2 operation. This rendered invalid
the subsequent computation of the high bits.
This commit fixes that by using a temporary register. The register
allocator can remove the redundant move in the common case when the
registers do not conflict.

Fixes #27046

7ab90288

by Rodrigo Mesquita at 2026-06-11T12:41:11-04:00

fix: make T27131 less flaky

It seems that T27131 fails flakily in a race where we check the flag
before the capability had the chance to process the mailbox which sets
the flag. This seemingly should only happen if the capability ends up
being the same for setting and checking the flag.

8965cb76
by Marc Scholten at 2026-06-12T04:53:22-04:00
```
haddock: render modules concurrently
```

8cc0b64a

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Promote HAVE_PREEMPTION from Timer.c to OSThreads.h

We will want to know about HAVE_PREEMPTION in more places.

HAVE_PREEMPTION tells us that we do have OS threads available,
irrespective of whether THREADED is defined. In particular,
HAVE_PREEMPTION is defined on all proper OSs, but not on WASM (and
hyopthetically may not be true on some other platforms like
micro-controllers, RTOSs, VM hypervisors etc).

cce574ed

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Define ACQUIRE_LOCK_ALWAYS and friends

Fix issue #27335

Like the atomic _ALWAYS variants, these lock actions are always defined,
rather than being dependent on whether we are in the THREADED case. All
the "normal" LOCK macros are defined to be no-ops when !THREADED.

The use case for the _ALWAYS variants is where we are using OS threads
even in the non-threaded RTS. This includes everything to do with the
timer/ticker thread, which is used in the non-threaded RTS too.

In particular, we will want to use this for eventlog things, because the
timer thread performs eventlogging concurrently with the main
capability, even in the non-threaded RTS.

1f28d1f6

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Use ACQUIRE/RELEASE_LOCK_ALWAYS with eventBufMutex

Even in the non-threaded RTS the eventBufMutex is needed by both the
main capability and the timer/ticker thread, so always use the mutex.

This should fix #25165 which is about the main capability and the timer
thread posting events to the eventlog buffer concurrently and thereby
corrupting the buffer data.

0ff29782

by Duncan Coutts at 2026-06-12T04:54:06-04:00

Expose eventBufMutex in the EventLog interface/header

We will need it in forkProcess to ensure we don't write to the global
eventlog buffer concurrently with trying to flush eventlog buffers and
do the fork().

7a688395

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Split flushAllCapsEventsBufs into safe and unlocked version

Following the convention that unlocked versions have a trailing _
underscore in their name. This one requires the caller to hold the
eventlog global buffer mutex. We will need this in forkProcess.

341ed474

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Remove redundant use of stopTimer in setNumCapabilities

Historically, the comment here was:

  We must stop the interval timer while we are changing the
  capabilities array lest handle_tick may try to context switch
  an old capability. See #17289.

and

  We must disable the timer while we do this since the tick handler may
  call contextSwitchAllCapabilities, which may see the capabilities array
  as we free it.

What this refers to is that historically, when changing the number of
capabilities, the array of capabilities was reallocated to a new size,
allocating new ones and freeing the old ones, thus invalidating all
existing capbility pointers.

Strangely, for good measure the code used to call stopTimer twice (hence
the two similar comments above).

However, since commit a3eccf06292dd666b24606251a52da2b466a9612, the
capabilities array is no longer reallocated. Instead the array is
allcoated once on RTS startup to the maximum size it could ever be
allowed to be, and then capabilities get enabled/disabled at runtime. So
the capability pointers never become invalid anymore. At worst, they may
point to capabilities that are disabled.

Thus we no longer need to stop the timer (twice) while we change the
number of enabled capabilities. This also partially solves issue #27105,
which notes that stopTimer is being used as if it were synchronous, when
it is not. At least for this case, the solution is that stopTimer is not
needed at all!

674858e3

by Duncan Coutts at 2026-06-12T04:54:07-04:00

Remove redundant use of stopTimer in forkProcess

but replace it with taking the eventlog buffer lock during the fork.

Fixes issue #27105

The original reason to block the timer during a fork was that
historically the timer was implemented using a periodic timer signal,
and the signal itself would interrupt the fork system call (returning
EINTR). For large processes (where fork() takes a while) this could
permanently livelock: the timer always would go off before the fork
could complete, which got retried in a loop forever.

The timer is no longer implemented as a unix signal, but uses threads.
Thus the original problem no longer exists. The only remaining reason to
block the timer tick is to prevent actions taken by the tick from
interfering with the delicate process involved in fork (taking a load of
locks and pausing everything).

The only thing we need to do is to prevent the eventlog from being
written to or flushed while the fork is taking place. To achieve this
all we need to do is hold the mutex for the global eventlog buffer.

This removes the last use of stopTimer that expects stopTimer to work
synchronously (which it was not) and thus solves issue #27105. To be
clear, we solve issue #27105 not by making stopTimer synchronous, but by
eliminating the use sites that expected it to be synchronous.

40764930

by sheaf at 2026-06-12T14:54:43-04:00

Add type family performance test for #26426

Some GHC versions produced large numbers of coercions after typechecking
and desugaring when compiling the program in #26426:

Version | Typechecker time | Typechecker allocations | Coercions
-------:|-----------------:|------------------------:|---------:
9.6     |   47 ms          |  48 MB                  |    110k
9.8     | 1000 ms          | 486 MB                  | 10,437k
9.10    |  922 ms          | 489 MB                  | 10,436k
9.12    |  906 ms          | 482 MB                  | 10,437k
9.14    |   63 ms          |  55 MB                  |    333k
10.0    |   47 ms          |  64 MB                  |     35k

The improvement 9.12 -> 9.14 was due to commit 22d11fa818fae2c95c494fc0fac1f8cb4c6e7cb6,
while the improvement 9.14 -> 10.0 was due to commit 0b7df6db9e46df40e86fbff1a66dc10440b99db5.

As the behaviour of GHC seems better than it's ever been on this program,
we declare victory, adding this performance test to ensure we don't
regress on this program.

On the way, we update Note [Combining equalities] in GHC.Tc.SolveR.Equality
with the explanation of the 9.12 -> 9.14 improvement (getting rid of an
exponential blowup in coercion sizes), and we update
Note [Exploiting closed type families] in GHC.Tc.Solver.FunDeps with
the explanation of the 9.14 -> 10.0 improvement (bringing down coercion
size growth from cubic to quadratic).

0f3d0a71

by Zubin Duggal at 2026-06-12T14:55:30-04:00

compiler: mark tool messages as errors/warnings depending on the exit code

Fixes #27370

d9ea2d76

by mangoiv at 2026-06-13T04:41:51-04:00

libraries/process: bump submodule to v1.6.30.0

- bump the submodule to the appropriate tag
- suppress benign warning resulting from the change

6ebaaba3

by David Eichmann at 2026-06-13T04:42:37-04:00

ghc-toolchain: don't throw when candidate executables are not found

Fixes #27369

6c65e1e1

by David Eichmann at 2026-06-13T04:43:23-04:00

CI: lint-changelog checks for no-changelog label in script instead of rules

bab37cc6

by konsumlamm at 2026-06-13T19:10:21+02:00

Implement CLC proposal #378

Add `Data.Double` and `Data.Float` modules
Document that GHC uses IEEE 754

fb5246ad

by fendor at 2026-06-15T18:07:23-04:00

Drop `preloadClosure` from `UnitState`

It is always hard-coded to the same value.

Backpack Unit instantiation isn't using it any more.
Allows us to simplify the API and get rid of `improveUnit`.

291ce3aa

by ARATA Mizuki at 2026-06-15T18:08:26-04:00

RISC-V NCG: Zero-extend the result of castFloatToWord32

According to the ISA manual, FMV.X.W sign-extends the result.
We need to truncate the result to avoid creating an exotic Word32 value.

Fixes #27300

011be91f

by ARATA Mizuki at 2026-06-15T18:08:26-04:00

RISC-V NCG: Treat d28-d31 (ft8-ft11) as caller-saved

According to the calling convention, the registers d28-d31 (ft8-ft11) are caller-saved.

Fixes #27306

e8a54713

by ARATA Mizuki at 2026-06-15T18:08:26-04:00

RISC-V NCG: Set rounding mode when emitting `truncate`

If we omit the rounding mode for `fcvt`, `dyn` will be used.
We do not want that for `truncate`, so we set `rtz`.
In other places, we set `rne` because we do not use the dynamic rounding mode.

Fixes #27303

9438bec7

by Zubin Duggal at 2026-06-15T18:09:11-04:00

rts: fix validate build with gcc 16. `__attribute__((regparm(1)))` is ignored on x86_64 and now
gcc warns that it is ignored:

rts/sm/Evac.h:35:1: error:
     error: ‘regparm’ attribute ignored [-Werror=attributes]

See https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ccead81bbc39668376eb5cf47066acb446cc43f3

Fixes #27366

893e6133

by Andrew Lelechenko at 2026-06-15T23:55:36+01:00

base: more NonEmpty zips

CLC proposal: https://github.com/haskell/core-libraries-committee/issues/409

1314f2fd
by David Eichmann at 2026-06-16T05:46:52-04:00
```
Hadrian: fix ghc-internal .def file name
```

7f72bcb3

by mangoiv at 2026-06-16T05:47:39-04:00

compiler: ignore camelCase and Eta reduce hlint hints

These do not cohere with the style used in GHC. After disabling them,
hlint lints are much less noisy again.

842bef9f
by Alan Zimmerman at 2026-06-16T05:48:25-04:00
```
EPA: Use standard type family declaration for Anno
```

f6d30767

by Wolfgang Jeltsch at 2026-06-16T15:32:34-04:00

Fix two issues in the documentation of pipeline interruption

One issue is a typo (“interreuptible”), the other one the lack of an end
of a sentence, which has been reconstructed from the message of
633bbc1fd4762a2bb73ba1c5b9e0c279f1dd3c40, the commit that introduced
said documentation.

a3fa10e0

by Christian Georgii at 2026-06-16T15:33:26-04:00

Find plugins in sibling home units in multiple-home-unit sessions

In a multiple-home-unit session (e.g. `cabal repl --enable-multi-repl` or HLS), enabling a plugin with -fplugin that is defined in (or reexported by) another home unit failed with a "hidden package" error. The plugin module finder only searched the current home unit and the registered external packages, never the sibling home units.

findPluginModuleNoHsc now searches the home units that the current home unit depends on, following module reexports and respecting hidden modules, exactly as ordinary import resolution does in findImportedModuleNoHsc. To avoid two divergent copies of this logic, the shared home-unit search (the current home unit first, then its dependencies in priority order, with the accompanying ordering invariant) is extracted into findHomeModuleAmongDeps, which both findImportedModuleNoHsc and findPluginModuleNoHsc now call.

Add testsuite/tests/driver/multipleHomeUnits/plugin01, which loads a plugin as byte-code from a sibling home unit, and plugin02, in which the consumer enables a plugin reexported by a sibling home unit without depending on the plugin's own home unit directly.

Fixes #27349

d216412b

by Ian-Woo Kim at 2026-06-16T20:25:57-04:00

Make the order of usages deterministic

It has been observed that the ordering of usages can be non-determinstic
in parallel builds. Therefore, this contribution introduces sorting of
usages based on a platform- and race-independent sorting criterion.

Resolves #26877.

Co-authored-by: Wolfgang Jeltsch <wolfgang@well-typed.com>

8e1cc105

by Wolfgang Jeltsch at 2026-06-16T20:25:57-04:00

Change the descriptions of two existing changelog entries

The descriptions now describe the changes in a user-friendly manner, as
opposed to describing the contributions that led to these changes in a
developer-friendly manner.

636c1c7a

by Ian Duncan at 2026-06-16T20:26:50-04:00

AArch64: use SXTH, not SXTW, for W32 signExtendReg

signExtendReg was using SXTH (sign-extend halfword, 16-bit) for
W32-to-W64 sign extension. This should be SXTW (sign-extend word,
32-bit). SXTH only sign-extends the lower 16 bits, producing wrong
results for 32-bit values whose bit 15 differs from bit 31.

Other fixes:

  - At sub-W64, code gen for MO_S_Mul2 should use W32 registers for
    SMULL source operands as per the ARM spec (SMULL Xd, Wn, Wm),
    and not W64.

  - Ensure signExtendReg uses the source width for the source operand
    in SXTW/SXTH/SXTB instructions. GNU as requires sxtw Xd,Wn (not
    sxtw Xd,Xn), while LLVM's integrated assembler on macOS is lenient.

  - Fix overflow flag computation for `MO_S_Mul2`. The overflow bit
    was exactly inverted for sub-W64 operands.

Fixes #26978 and #27047

b734c75d

by Igor Ranieri at 2026-06-16T20:27:32-04:00

haddock: Update CONTRIBUTING with missing step, add missing test
dependency

7fe4f2ec

by Luite Stegeman at 2026-06-17T05:35:09-04:00

tag inference: don't confuse functions with their return values

inferTagRhs was mixing up taggedness for closures and return values
for function closures. We really shouldn't assign TagTuple to a
properly tagged function returning a tuple.

We fix this by keeping track of functions (TagFun) separately from
values (TagVal) and keeping track of their return value. TagFun is
also used for join points.

fixes #27005

4671c126

by Sebastian Graf at 2026-06-17T05:35:55-04:00

Seed the simplifier's in-scope set for open expressions

simplifyExpr simplifies expressions typed at the GHCi prompt and the
results of Template Haskell splices. Such an expression may be open: at a
GHCi debugger breakpoint its free variables include RuntimeUnk skolems
standing for as-yet-unknown types.

The simplifier began with an in-scope set holding only the wildcard
binder, so when it instantiated the unsafeCoerce# wrapper that GHCi
builds around a result, it formed a substitution whose range mentioned a
free skolem that was not in scope. That breaks the substitution invariant
and, in a compiler built with assertions, trips substTy's sanity check.

Seed the initial in-scope set with the free variables of the expression.
For a closed expression this adds nothing.

See Note [Seed the in-scope set for open expressions].

Fixes #17833 and its duplicate #21118.

67d41299

by Sebastian Graf at 2026-06-18T05:18:24-04:00

Desugar a `case` scrutinee only once (#27383, #20251)

In `dsExpr` for `HsCase` we desugared the scrutinee /twice/: once to
build the Core `case` itself, and again inside `matchWrapper`, which
re-desugared the source scrutinee (via `addHsScrutTmCs`) purely to
record long-distance information for the pattern-match checker.

For a single `case` that is merely wasteful.  But for nested cases it
is catastrophic.  Consider

    case (case (case e of ... ) of ... ) of ...

Desugaring the outer scrutinee desugars the middle `case` twice, each
of which desugars the inner `case` twice, and so on.  The work doubles
at every level, so desugaring takes O(2^n) time in the nesting depth.
That is the blowup reported in #27383; it is also what makes the
machine-generated program in #20251 take an age to compile.

The fix is simple.  `matchWrapper` is handed the scrutinee anyway, so
we give it the Core expression we have /already/ desugared, and record
the long-distance term constraint with `addCoreScrutTmCs` instead of
re-desugaring from source.  This is just what `matchSinglePatVar`
already does for single-pattern matches.

So:

* `matchWrapper` now takes `Maybe [CoreExpr]` rather than
  `Maybe [LHsExpr GhcTc]`.

* The `HsCase` equation of `dsExpr` passes the already-desugared
  `core_discrim`; the arrow desugarer passes its match variables.

* `addHsScrutTmCs` had no other use, so it is gone.

Desugaring is now linear in the nesting depth.  (The coverage checker
still runs `simpleOptExpr` over each scrutinee, which leaves the total
at O(n^2); that is ample.)  The long-distance information itself is
unchanged: the checker sees precisely the Core that backs the
generated code.

Test: deSugar/should_compile/T27383

fa5defde

by Rodrigo Mesquita at 2026-06-18T05:19:11-04:00

fix: Save FastStrings in the PMC

There is no point in adding the unique to the occurrence FastString we
create, since it is part of the Id anyway.

Adding it to the FastString, meant each FastString was unique
unnecessarily!

In a separate branch, running the compiler on test `InstanceMatching`
observed 30000 `FastString`s created by this code path.

Plus, `fsLit "pm"` follows the existing pattern in `mkPmId`.

4efb4a66

by Alan Zimmerman at 2026-06-18T14:41:14-04:00

TTG: Add extension points to HsConDetails

Extend HsConDetails as

    data HsConDetails p arg rec
      = PrefixCon !(XPrefixCon p) [arg]    -- C @t1 @t2 p1 p2 p3
      | RecCon    !(XRecCon p)    rec      -- C { x = p1, y = p2 }
      | InfixCon  !(XInfixCon p)  arg arg  -- p1 `C` p2
      | XHsConDetails !(XXHsConDetails p)

    type family XPrefixCon      p
    type family XRecCon         p
    type family XInfixCon       p
    type family XXHsConDetails  p

c8d27dd4

by Simon Jakobi at 2026-06-18T14:41:59-04:00

CI: quiet submodule clean output in after_script and setup

The clean and cleanup_submodules functions ran 'git submodule foreach
git clean -xdf', flooding the job log with 'Entering ...' and
'Removing ...' lines. Pass --quiet to 'git submodule' and -q to 'git
clean' to drop the success output; errors are still reported.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

09326ca6

by Matthew Pickering at 2026-06-20T23:41:12+02:00

Add missing req_interp modifier to T18441fail3 and T18441fail19

These tests require the interpreter but they were failing in a different
way with the javascript backend because the interpreter was disabled and
stderr is ignored by the test.

521e55bf

by Matthew Pickering at 2026-06-20T23:41:13+02:00

hadrian: Fill in more of the default.host toolchain file

When you are building a cross compiler this file will be used to build
stage1 and it's libraries, so we need enough information here to work
accurately. There is still more work to be done (see for example, word
size is still fixed).

23c9b6c3

by Matthew Pickering at 2026-06-20T23:42:52+02:00

hadrian: Build stage 2 cross compilers

* Most of hadrian is abstracted over the stage in order to remove the
  assumption that the target of all stages is the same platform. This
  allows the RTS to be built for two different targets for example.
* Abstracts the bindist creation logic to allow building either normal
  or cross bindists. Normal bindists use stage 1 libraries and a stage 2
  compiler. Cross bindists use stage 2 libararies and a stage 2
  compiler.
* 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

New hadrian target:

* `binary-dist-dir-cross`: Build a cross compiler bindist (compiler =
  stage 1, libraries = stage 2)

This commit also contains various changes to make stage2 compilers
feasible.

-------------------------
Metric Decrease:
    LinkableUsage02
    ManyAlternatives
    ManyConstructors
    MultiComponentModulesRecomp
    MultiLayerModulesRecomp
    RecordUpdPerf
    T10421
    T12150
    T12227
    T12425
    T12707
    T13035
    T13379
    T13820
    T15703
    T16577
    T18140
    T18282
    T18698a
    T18698b
    T18923
    T1969
    T20049
    T21839c
    T3294
    T4801
    T5030
    T5321FD
    T5321Fun
    T5631
    T5642
    T6048
    T783
    T9020
    T9198
    T9233
    T9630
    T9872d
    T9961
    parsing001
    T3064

Metric Increase:
    T26989
    hard_hole_fits
-------------------------

Co-authored-by: Sven Tennie <sven.tennie@gmail.com>

26fed8ab

by Matthew Pickering at 2026-06-20T23:42:52+02:00

ci: Test cross bindists

We remove the special logic for testing in-tree cross
compilers and instead test cross compiler bindists, like we do for all
other platforms.

80c8910e

by Matthew Pickering at 2026-06-20T23:42:52+02:00

ci: Introduce CROSS_STAGE variable

In preparation for building and testing stage3 bindists we introduce the
CROSS_STAGE variable which is used by a CI job to determine what kind of
bindist the CI job should produce.

At the moment we are only using CROSS_STAGE=2 but in the future we will
have some jobs which set CROSS_STAGE=3 to produce native bindists for a
target, but produced by a cross compiler, which can be tested on by
another CI job on the native platform.

CROSS_STAGE=2: Build a normal cross compiler bindist
CROSS_STAGE=3: Build a stage 3 bindist, one which is a native compiler and library for the target

8215573d

by Sven Tennie at 2026-06-20T23:42:52+02:00

ci: Increase timeout for emulators

Test runs with emulators naturally take longer than on native machines.

Generate jobs.yml

5acb7dbc

by Matthew Pickering at 2026-06-20T23:42:52+02:00

ci: Javascript don't set CROSS_EMULATOR

There is no CROSS_EMULATOR needed to run javascript binaries, so we
don't set the CROSS_EMULATOR to some dummy value.

48345343

by Sven Tennie at 2026-06-20T23:42:52+02:00

Javascript skip T23697

See #22355 about how HSC2HS and the Javascript target don't play well
together.

5e44fd05

by Sven Tennie at 2026-06-20T23:42:52+02:00

Mark T24602 as fragile

It was skipped before (due to CROSS_EMULATOR being set, which changed
for JS), so we don't make things worse by marking it as fragile.

ab349ec2

by Sven Tennie at 2026-06-20T23:42:52+02:00

Fix T22744 for GHCJS

In fact, this test needs Template Haskell, not necessarily an
interpreter.

c73352d8

by Sven Tennie at 2026-06-20T23:42:52+02:00

haddock-test: fix GHCJS haddock test failures

Add --ghc-pkg-path flag support so haddock test runner can find
cross-prefixed ghc-pkg (e.g. javascript-unknown-ghcjs-ghc-pkg) which
is not on $PATH in cross install directories.

Skip haddockHtmlTest on GHCJS: Threaded.hs uses forkOS in a TH splice,
which GHCJS RTS doesn't support. Mark with js_skip in all.T.

5e814e76

by Andreas Klebinger at 2026-06-22T23:00:24-04:00

compiler: Deduplicate hscTidy

This function was accidentally duplicated during a refactor.

Fixes #27351

473b97eb

by sheaf at 2026-06-22T23:01:22-04:00

Avoid mkTick in Core Prep breaking ANF (part II)

Hotfix for 2f9579765f55b3920ceb2e04995ff41a9d0e2d4e fixing a small
oversight in the call to tickTickedExpr from mkTick, in which we
improperly recursively called mkTick without passing on the preserve_anf
flag.

Fixes #27386

3b3e2125

by Cheng Shao at 2026-06-23T09:50:14+02:00

rts: add is-valid-utf8.c to .ubsan-suppressions

A minor one in `bytestring` that might surface when building with
+ubsan using clang.

78f88661

by Cheng Shao at 2026-06-23T08:30:23+00:00

hadrian: add support for building with AddressSanitizer

This patch adds a +asan flavour transformer to hadrian to build all
stage1+ C/C++ code with AddressBehaviorSanitizer. This is particularly
useful to catch potential out-of-bounds and use-after-free bugs in the
RTS codebase.

3e5e4c95