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Sven Tennie pushed to branch wip/romes/hadrian-cross-stage2-rebase_SVEN_FINAL at Glasgow Haskell Compiler / GHC

Commits:

8f209336

by Simon Jakobi at 2026-01-05T16:24:48-05:00

User's guide: Fix link to language extensions

Instead of linking to haddocks, it seemed more useful to link
to the extension overview in the user's guide.

Closes #26614.

0b7df6db

by Simon Peyton Jones at 2026-01-06T09:32:23-05:00

Improved fundeps for closed type families

The big payload of this commit is to execute the plan suggested
in #23162, by improving the way that we generate functional
dependencies for closed type families.

It is all described in Note [Exploiting closed type families]

Most of the changes are in GHC.Tc.Solver.FunDeps

Other small changes

* GHC.Tc.Solver.bumpReductionDepth.  This function brings together the code that
   * Bumps the depth
   * Checks for overflow
  Previously the two were separated, sometimes quite widely.

* GHC.Core.Unify.niFixSubst: minor improvement, removing an unnecessary
  itraetion in the base case.

* GHC.Core.Unify: no need to pass an InScopeSet to
  tcUnifyTysForInjectivity. It can calculate one for itself; and it is
  never inspected anyway so it's free to do so.

* GHC.Tc.Errors.Ppr: slight impovement to the error message for
  reduction-stack overflow, when a constraint (rather than a type) is
  involved.

* GHC.Tc.Solver.Monad.wrapUnifier: small change to the API

fde8bd88

by Simon Peyton Jones at 2026-01-06T09:32:23-05:00

Add missing (KK4) to kick-out criteria

There was a missing case in kick-out that meant we could fail
to solve an eminently-solvable constraint.

See the new notes about (KK4)

00082844

by Simon Peyton Jones at 2026-01-06T09:32:23-05:00

Some small refactorings of error reporting in the typechecker

This is just a tidy-up commit.

* Add ei_insoluble to ErrorItem, to cache insolubility.
  Small tidy-up.

* Remove `is_ip` and `mkIPErr` from GHC.Tc.Errors; instead enhance mkDictErr
  to handle implicit parameters.  Small refactor.

fe4cb252

by Simon Peyton Jones at 2026-01-06T09:32:24-05:00

Improve recording of insolubility for fundeps

This commit addresses #22652, by recording when the fundeps for
a constraint are definitely insoluble.  That in turn improves the
perspicacity of the pattern-match overlap checker.

See Note [Insoluble fundeps]

df0ffaa5

by Simon Peyton Jones at 2026-01-06T09:32:24-05:00

Fix a buglet in niFixSubst

The MR of which this is part failed an assertion check extendTvSubst
because we extended the TvSubst with a CoVar.  Boo.

This tiny patch fixes it, and adds the regression test from #13882
that showed it up.

3d6aba77
by konsumlamm at 2026-01-06T09:33:16-05:00
```
Fix changelog formatting
```

69e0ab59

by Cheng Shao at 2026-01-06T19:37:56-05:00

compiler: add targetHasRTSWays function

This commit adds a `targetHasRTSWays` util function in
`GHC.Driver.Session` to query if the target RTS has a given Ways (e.g.
WayThreaded).

25a0ab94

by Cheng Shao at 2026-01-06T19:37:56-05:00

compiler: link on-demand external interpreter with threaded RTS

This commit makes the compiler link the on-demand external interpreter
program with threaded RTS if it is available in the target RTS ways.
This is a better default than the previous single-threaded RTS, and it
enables the external interpreter to benefit from parallelism when
deserializing CreateBCOs messages.

92404a2b

by Cheng Shao at 2026-01-06T19:37:56-05:00

hadrian: link iserv with threaded RTS

This commit makes hadrian link iserv with threaded RTS if it's
available in the RTS ways. Also cleans up the iserv main C program
which can be replaced by the `-fkeep-cafs` link-time option.

99a08fb8

by Matthew Pickering at 2026-01-15T18:30:03+01:00

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.

28627db3
by Matthew Pickering at 2026-01-15T18:30:03+01:00
```
Use explicit syntax rather than pure
```

fc74e652

by Matthew Pickering at 2026-01-15T18:30:03+01:00

packaging: correctly propagate build/host/target to bindist configure script

At the moment the host and target which we will produce a compiler for
is fixed at the initial configure time. Therefore we need to persist
the choice made at this time into the installation bindist as well so we
look for the right tools, with the right prefixes at install time.

In the future, we want to provide a bit more control about what kind of
bindist we produce so the logic about what the host/target will have to
be written by hadrian rather than persisted by the configure script. In
particular with cross compilers we want to either build a normal stage 2
cross bindist or a stage 3 bindist, which creates a bindist which has a
native compiler for the target platform.

Fixes #21970

4459c806

by Matthew Pickering at 2026-01-15T18:30:03+01:00

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).

ddd58cc7

by Matthew Pickering at 2026-01-15T18:30:03+01:00

hadrian: Disable docs when cross compiling

Before there were a variety of ad-hoc places where doc building was
disabled when cross compiling.

* Some CI jobs sets --docs=none in gen_ci.hs
* Some CI jobs set --docs=none in .gitlab/ci.sh
* There was some logic in hadrian to not need the ["docs"] target when
  making a bindist.

Now the situation is simple:

* If you are cross compiling then defaultDocsTargets is empty by
  default.

In theory, there is no reason why we can't build documentation for cross
compiler bindists, but this is left to future work to generalise the
documentation building rules to allow this (#24289)

863e37cb

by Matthew Pickering at 2026-01-15T19:41:37+01:00

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:
    ManyAlternatives
    MultiComponentModulesRecomp
    MultiLayerModulesRecomp
    T10421
    T12425
    T12707
    T13035
    T13379
    T15703
    T16577
    T18698a
    T18698b
    T18923
    T1969
    T21839c
    T3294
    T4801
    T5030
    T5321Fun
    T5642
    T783
    T9198
    T9872d
    T9961
    parsing001
    T5321FD
    T6048
-------------------------

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

9e41f664
by Sven Tennie at 2026-01-15T19:41:38+01:00
```
Align CI scripts with master

Fixup
```

b2ed8a03

by Matthew Pickering at 2026-01-15T19:41:38+01:00

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.

a1fc3497

by Matthew Pickering at 2026-01-15T19:41:38+01:00

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

c0a5e97d

by Matthew Pickering at 2026-01-15T19:41:38+01:00

hadrian: Refactor system-cxx-std-lib rules0

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`.

Fixes #25303

31090291