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Alan Zimmerman pushed to branch wip/az/exactprint-annotation-rationalisation at Glasgow Haskell Compiler / GHC

Commits:

9e7739ab

by Simon Jakobi at 2026-09-03T13:45:43-04:00

Add -Wimplicit-field-strictness (#16836)

This opt-in warning fires when a data constructor field lacks an
explicit strictness annotation (`!` or `~`).  It complements the
LazyFieldAnnotations extension (4762a8bf30f) from GHC proposal 752,
which makes `~` annotations available for this purpose.

Deciding which fields to report requires their levity, so the check
runs after typechecking.  To keep the noise down, the diagnostic is
emitted once per data declaration, grouped by constructor.

Closes #16836.

Assisted-by: Claude Fable 5

6a44d591

by mangoiv at 2026-09-03T13:46:22-04:00

simplifier: remove a bogus `assert` in `rebuild_app'` in `GHC.CoreToStg.Prep.cpeApp`.

Prior to this commit
    commit 08bc245be70d95801bc1138804ed1de9474fbdc0
    Author: sheaf <sam.derbyshire@gmail.com>
    Date:   Sat Feb 28 16:30:43 2026 +0100

    Clean up join points, casts & ticks

    This commit shores up the logic dealing with casts and ticks occurring
    in between a join point binding and a jump

any `PlaceRuntime` ticks we observed were profiling ticks, even though that
isn't necessary.
The more liberal rules in the above commit allow e.g. breakpoint ticks
(which are valid PlaceRuntime ticks) to legitimately appear in an argument
position.

Fixes #27556

eaa95a6f

by Andrei Borzenkov at 2026-09-04T08:08:40-04:00

Parentheses in prefix GADT constructors (#27423)

Updated `splitLHsGadtTy` to allow looking
through the parentheses for inner binders. General example
of a code pattern that's allowed now:

  data S a where
    MkS :: (forall a. S a)

That should work now with any combination of nested
foralls and parentheses.

We don't perform parenthesis unwrapping for record
GADT constructors in accordance with GHC Proposal #402.

To this end `con_inner_bndrs` no longer stores plain forall
telescopes: `[HsForAllTelescope pass]` is replaced with
`[LHsGadtTelescope pass]`, a new `HsArg`-style type whose
`HsGadtForAll` holds an inner telescope and whose `HsGadtPar`
holds a pair of parentheses. The parentheses carry no meaning
for renaming or type checking; the only reason to record them
is exact-printing.

Updated `pprConDecl` to improve the `parse == parse . ppr . parse`
property of GADT pretty-printing.

The pretty printer can now output code that's similar to this:

  data T a where
    MkT1 :: (forall a. T a)
    MkT2 :: forall . forall a. T a

These are special cases of inner forall binders
for prefix GADT constructors, when we have either
implicit or zero explicit outer binders.

639456a8

by Evgeny Malyshev at 2026-09-04T08:09:25-04:00

HsPat: Add spacing to unary tuple patterns

Use hsep when printing unary boxed TuplePat applications so that the
MkSolo constructor is separated from its argument. The old hcat rendered
wildcard and parenthesized arguments as MkSolo_ and MkSolo().

Add T27034 to exercise the HsPat splice-dump path with wildcard and
variable arguments, and update existing affected golden output.

Fixes #27034

Assisted-By: OpenAI Codex

2908ab36

by Simon Jakobi at 2026-09-05T07:22:17-04:00

X86 NCG: use btr/bts/btc for single-bit operations

Previously the Cmm patterns

  x & ~(1 << i)
  x | (1 << i)
  x ^ (1 << i)

compiled to mov/shl/not/and-style sequences of 3-4 instructions. Now
they compile to a single btr, bts or btc, matching what C compilers
produce.

When the bit index is a literal, constant folding has already collapsed
these patterns into ones with a literal mask, such as
x & 0xfffffeffffffffff for x & ~(1 << 40). Such masks are now also
compiled to a bit-test instruction when they don't fit in an imm32 and
would otherwise have to be loaded into a register first.

For a variable bit index, this applies only when the shift is unchecked
(uncheckedShiftL#, Data.Bits.unsafeShiftL): the bounds-checked shiftL
used by e.g. the default clearBit/setBit/complementBit implementations
wraps the shift in a bounds mask that this optimisation does not see
through. With a literal index, the bounds mask is constant-folded away,
so the checked operations benefit too.

See Note [Bit-test instructions] in GHC.CmmToAsm.X86.CodeGen.

Fixes #25233.

Assisted-by: Claude Fable 5

c673ecf0

by Simon Peyton Jones at 2026-09-05T07:22:59-04:00

Move HsStatic free-var test to typechecker

A `static` form should have no free *term* variables, but it
can have free *type* variables.  Alas, the renamer does not really know what
is a term variable and what is a type variable, because of required type
arguments. This patch moves the test to the typechecker, which does know.

Addresses #27664

5939ceaf

by sheaf at 2026-09-05T22:06:18-04:00

Windows: enforce path convention in ./configure

As detailed in Note [MSYS paths] in Hadrian.Utilities, the standing
convention (using Windows-style paths with forward slashes) is now
enforced in ./configure instead of within Hadrian, removing the need for
'cygpath' calls within Hadrian.

Fixes #26683

a6061455

by sheaf at 2026-09-05T22:06:18-04:00

Hadrian: introduce ExeSpawnPath

Specific details about the filepath used to specify the executable to
spawn with CreateProcess matters on Windows: whether we use forward or
backward slashes, a leading ./, or an absolute path changes how the
executable is found.

This commit introduces 'ExeSpawnPath' which is a path that is guaranteed
to be found when spawning a process. All command invocations now go
through this type to ensure the path has been properly sanitised.

See Note [NeedCurrentDirectoryForExePath] in Hadrian.Utilities.

The same treatment is applied to hsc2hs. Updates hsc2hs submodule.

e28313e3

by sheaf at 2026-09-05T22:07:06-04:00

Preserve tick ordering in 'tickTickedExpr'

'GHC.Core.Utils.tickTickedExpr' tries to combine a tick 't1' into an
existing stack of ticks 't2s'. There are two situations:

  1. 't1' is subsumed by a tick in 't2s': drop it.
  2. A tick in 't2s' is subsumed by 't1', say 't2'.

This commit ensures that in case (2) we keep 't1' on the outside instead
of replacing 't2' at its position in the stack. This avoids re-ordering
source notes (which was the cause of #27749).

This fixes a regression introduced in 2dadf3b0d05.

Fixes #27749

3172f557

by sheaf at 2026-09-05T22:07:06-04:00

Consistently prefer local source note ticks

GHC.Cmm.DebugBlock.cmmDebugGen (DWARF annotations) and
GHC.Stg.Debug.quickSourcePos (-finfo-table-map) both contained logic to
prioritise source note ticks from the current module.

This commit commons up this logic and propagates it to a third consumer:
IPE stack frames, in GHC.Driver.GenerateCgIPEStub.
See the new function GHC.Types.Tickish.bestSourceNote.

f45a3d8e