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Ben Gamari pushed to branch wip/T25716 at Glasgow Haskell Compiler / GHC

Commits:

3b3a5dec

by Ben Gamari at 2025-05-15T16:10:01-04:00

Don't emit unprintable characters when printing Uniques

When faced with an unprintable tag we now instead print the codepoint
number.

Fixes #25989.

(cherry picked from commit e832b1fadee66e8d6dd7b019368974756f8f8c46)

e1ef8974

by Mike Pilgrem at 2025-05-16T16:09:14-04:00

Translate iff in Haddock documentation into everyday English

fd64667d

by Vladislav Zavialov at 2025-05-20T03:25:08-04:00

Allow the 'data' keyword in import/export lists (#25899)

This patch introduces the 'data' namespace specifier in import and
export lists. The intended use is to import data constructors without
their parent type constructors, e.g.

  import Data.Proxy as D (data Proxy)
  type DP = D.Proxy   -- promoted data constructor

Additionally, it is possible to use 'data' to explicitly qualify any
data constructors or terms, incl. operators and field selectors

  import Prelude (Semigroup(data (<>)))
  import Data.Function (data (&))
  import Data.Monoid (data Dual, data getDual)

  x = Dual "Hello" <> Dual "World" & getDual

The implementation mostly builds on top of the existing logic for the
'type' and 'pattern' namespace specifiers, plus there are a few tweaks
to how we generate suggestions in error messages.

acc86753

by Ben Gamari at 2025-05-20T03:25:51-04:00

compiler: Use field selectors when creating BCOs

This makes it easier to grep for these fields.

60a55fd7

by Ben Gamari at 2025-05-20T03:25:51-04:00

compiler: Clarify BCO size

Previously the semantics and size of StgBCO was a bit unclear.
Specifically, the `size` field was documented to contain the size of the
bitmap whereas it was actually the size of the closure *and* bitmap.
Additionally, it was not as clear as it could be that the bitmap was a
full StgLargeBitmap with its own `size` field.

ac9fb269

by Simon Peyton Jones at 2025-05-20T09:19:04-04:00

Track rewriter sets more accurately in constraint solving

This MR addresses #26003, by refactoring the arcane
intricacies of Note [Equalities with incompatible kinds].
NB: now retitled to
    Note [Equalities with heterogeneous kinds].
and the main Note for this MR.

In particular:

* Abandon invariant (COERCION-HOLE) in Note [Unification preconditions] in
  GHC.Tc.Utils.Unify.

* Abandon invariant (TyEq:CH)) in Note [Canonical equalities] in
  GHC.Tc.Types.Constraint.

* Instead: add invariant (REWRITERS) to Note [Unification preconditions]:
  unify only if the constraint has an empty rewriter set.

Implementation:

* In canEqCanLHSFinish_try_unification, skip trying unification if there is a
  non-empty rewriter set.

* To do this, make sure the rewriter set is zonked; do so in selectNextWorkItem,
  which also deals with prioritisation.

* When a coercion hole is filled, kick out inert equalities that have that hole
  as a rewriter.  It might now be unlocked and available to unify.

* Remove the ad-hoc `ch_hetero_kind` field of `CoercionHole`.

* In `selectNextWorkItem`, priorities equalities withan empty rewriter set.

* Defaulting: see (DE6) in Note [Defaulting equalities]
  and Note [Limited defaulting in the ambiguity check]

* Concreteness checks: there is some extra faff to try to get decent
  error messages when the FRR (representation-polymorphism) checks
  fail. In partiular, add a "When unifying..." explanation when the
  representation-polymorphism check arose from another constraint.

86406f48

by Cheng Shao at 2025-05-20T09:19:47-04:00

rts: fix rts_clearMemory logic when sanity checks are enabled

This commit fixes an RTS assertion failure when invoking
rts_clearMemory with +RTS -DS. -DS implies -DZ which asserts that free
blocks contain 0xaa as the designated garbage value. Also adds the
sanity way to rts_clearMemory test to prevent future regression.
Closes #26011.

ChatGPT Codex automatically diagnosed the issue and proposed the
initial patch in a single shot, given a GHC checkout and the following
prompt:

---

Someone is reporting the following error when attempting to use `rts_clearMemory` with the RTS option `-DS`:

```
test.wasm: internal error: ASSERTION FAILED: file rts/sm/Storage.c, line 1216

    (GHC version 9.12.2.20250327 for wasm32_unknown_wasi)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
```

What's the culprit? How do I look into this issue?

---

I manually reviewed & revised the patch, tested and submitted it.

7147370b