Prepare 12.3.1 maintenance release by cknitt · Pull Request #8565 · rescript-lang/rescript

cknitt · 2026-08-19T10:57:25Z

Summary

Prepare the conservative ReScript 12.3.1 maintenance release from maintenance/12.x.

The fixes were backported chronologically and adapted where necessary to avoid pulling newer infrastructure or broad refactors:

Fix rewatch warning replay after early compile errors #8408: replay stored Rewatch warnings after an early compile error
Fix formatting of trailing comments before equals #8444: format trailing comments before = correctly
analysis: fix namespaced reference lookup #8455: fix namespaced reference lookup
Fix build crash when compiler output is not valid UTF-8 #8482: avoid a Rewatch crash on invalid UTF-8 compiler output
Preserve multibyte characters when wrapping long source lines #8520: preserve multibyte characters when wrapping compiler code frames
Fix exponentiation precedence for compound exponents #8550: preserve compound exponent precedence
Enforce function arity in type inclusion and coercion #8559: backport only the three missing function-arity type-system guards and focused regressions
Record written arrow arity before external lowering #8563: backport only the independent bare labeled-arrow arity fix
Make functions and arrow types n-ary in the parsetree #8566: fix signature help for functions returning functions, including the parameter ranges
Fix argument evaluation order under function inlining #8572: preserve argument evaluation order when functions are inlined
Make the typed layers n-ary: Tarrow params and Texp_function params #8568: extract the independent fix that evaluates optional defaults at their own parameter group
Make the typed layers n-ary: Tarrow params and Texp_function params #8568: extract the independent fix that carries termination analysis through helper functions
set compiler, runtime, platform package, and Rewatch versions to 12.3.1

Scope

This intentionally excludes larger or more invasive master changes, notably:

Fix incorrect analysis report for optional function args #8321, the large reanalyze change
Harden the Parsetree0 PPX bridge #8561, the combined PPX bridge and wire-format refactor
the broader diagnostic-reporting portion of Enforce function arity in type inclusion and coercion #8559
the phantom-argument parser/printer rewrite from Record written arrow arity before external lowering #8563
the broader n-ary series refactor from Make the typed layers n-ary: Tarrow params and Texp_function params #8568; only its two isolated correctness fixes are included

The goal is to fix concrete correctness and crash issues without increasing maintenance-release regression risk.

Validation

make test
make test-analysis
make test-syntax
make test-rewatch
make checkformat
focused termination-analysis test corpus
Rewatch Rust unit tests and formatting checks
complete GitHub Actions matrix, including compiler builds, analysis/tools, installation, API docs, package preview, and Rewatch integration tests

All local checks pass, and CI is green across the full matrix.

Backport the fix by tracking modules that actually recompiled, so stored warnings are replayed for dependents skipped after an earlier error. (cherry picked from commit 56d4ed5) Signed-off-by: Christoph Knittel <ck@cca.io>

* analysis: fix namespaced reference lookup * analysis: demonstrate incremental CMT lookup

pkg-pr-new · 2026-08-19T11:46:15Z

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@rescript/runtime

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@rescript/win32-x64

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commit: f8aa648

Adapted from 7f15521 for the 12.3.x Rewatch test layout.

* Preserve multibyte characters when wrapping long source lines in compiler code frames * Changelog

* Fix exponentiation right operand precedence Signed-off-by: Christoph Knittel <ck@cca.io> * Update changelog for exponentiation precedence fix Signed-off-by: Christoph Knittel <ck@cca.io> --------- Signed-off-by: Christoph Knittel <ck@cca.io>

Backport only the three type-system guards and focused regressions from 8fafaf9; omit the larger diagnostic-reporting refactor.

Backport only the independent bare labeled-arrow fix from 110534a; omit the broader external phantom-argument parser/printer rewrite.

Adapted from 5e23370 for the 12.x arity-marked parsetree. Signed-off-by: Christoph Knittel <ck@cca.io>

Lam_beta_reduce built the bindings for non-substitutable arguments by prepending during fold_left2 (reverse parameter order) and then wrapped the body with fold_right, making the first parameter's binding innermost - so the last argument was evaluated first. Fold left instead, so the first parameter's binding is outermost and arguments evaluate in call order. The reversed order was visible in checked-in output: bs_set_int_test.mjs evaluated setEqArray's second argument before its first. The new inline_arg_order_test fixture pins the order with recursive (hence non-substitutable) effectful arguments; its checked-in JS would show the regression directly. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com> (cherry picked from commit 124bc4b)

Adapted from d0440c3 for the 12.x arity-marked typedtree. Signed-off-by: Christoph Knittel <ck@cca.io>

Adapted from d0440c3 for the 12.x typedtree. Signed-off-by: Christoph Knittel <ck@cca.io>

Signed-off-by: Christoph Knittel <ck@cca.io>

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chatgpt-codex-connector · 2026-08-21T08:58:17Z

 > - :nail_care: [Polish]
 > - :house: [Internal]

+# 12.3.1


Sign off the release commit

The reviewed commit message has no Signed-Off-By: trailer, although this repository requires DCO sign-off for commits; add the author sign-off before merging the release commit.

AGENTS.md reference: AGENTS.md:L240-L243

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chatgpt-codex-connector · 2026-08-21T08:58:17Z

+let _ = {
+  helper(effA(0), effB(0))
+}


Use ignore for the side-effect-only call

This binding exists only to evaluate helper(effA(0), effB(0)) and discard its result, but repository guidance explicitly prohibits let _ = … for side effects; use ignore helper(effA(0), effB(0)) so the regression test follows the required convention.

AGENTS.md reference: AGENTS.md:L44-L45

Useful? React with 👍 / 👎.

chatgpt-codex-connector · 2026-08-21T08:58:17Z

+- Fix bare labeled arrow types (`~x: int => string`) getting no arity and failing to unify with their parenthesized form. https://github.com/rescript-lang/rescript/pull/8563
+- Fix argument evaluation order when a function call is inlined: the beta reducer could evaluate non-substitutable arguments from last to first. https://github.com/rescript-lang/rescript/pull/8572


Document the signature-help fix

The commit backports the #8566 SignatureHelp.ml fix and its tests, but the 12.3.1 release notes jump directly from #8563 to #8572. Users consulting this changelog therefore cannot discover that functions returning functions now expose the correct outer parameters and ranges; add the missing #8566 entry before releasing.

Useful? React with 👍 / 👎.

cknitt and others added 3 commits August 19, 2026 11:17

Fix rewatch warning replay after early compile errors (#8408)

5aafa89

Backport the fix by tracking modules that actually recompiled, so stored warnings are replayed for dependents skipped after an earlier error. (cherry picked from commit 56d4ed5) Signed-off-by: Christoph Knittel <ck@cca.io>

Fix formatting of trailing comments before equals (#8444)

96e18fb

analysis: fix namespaced reference lookup (#8455)

5560f61

* analysis: fix namespaced reference lookup * analysis: demonstrate incremental CMT lookup

nathan-tranquilla and others added 5 commits August 21, 2026 08:37

Fix build crash when compiler output is not valid UTF-8 (#8482)

33952c1

Adapted from 7f15521 for the 12.3.x Rewatch test layout.

Preserve multibyte characters when wrapping long source lines (#8520)

6eef756

* Preserve multibyte characters when wrapping long source lines in compiler code frames * Changelog

Enforce function arity in inclusion, type equality, and coercion (#8559)

f081e33

Backport only the three type-system guards and focused regressions from 8fafaf9; omit the larger diagnostic-reporting refactor.

Record arity for bare labeled arrow types (#8563)

c237eab

Backport only the independent bare labeled-arrow fix from 110534a; omit the broader external phantom-argument parser/printer rewrite.

cknitt force-pushed the codex/12.3.1 branch from a1ad1df to 093059b Compare August 21, 2026 06:37

cristianoc and others added 4 commits August 21, 2026 10:03

Fix signature help for functions returning functions

38fda64

Adapted from 5e23370 for the 12.x arity-marked parsetree. Signed-off-by: Christoph Knittel <ck@cca.io>

Fix timing of optional defaults in curried functions

7dfea30

Adapted from d0440c3 for the 12.x arity-marked typedtree. Signed-off-by: Christoph Knittel <ck@cca.io>

Fix termination analysis through helper functions

f940ad2

Adapted from d0440c3 for the 12.x typedtree. Signed-off-by: Christoph Knittel <ck@cca.io>

cknitt force-pushed the codex/12.3.1 branch from 4442efb to 3336296 Compare August 21, 2026 08:03

Set version to 12.3.1

f8aa648

Signed-off-by: Christoph Knittel <ck@cca.io>

cknitt force-pushed the codex/12.3.1 branch from 3336296 to f8aa648 Compare August 21, 2026 08:05

cknitt marked this pull request as ready for review August 21, 2026 08:55

chatgpt-codex-connector Bot reviewed Aug 21, 2026

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Prepare 12.3.1 maintenance release - #8565

Prepare 12.3.1 maintenance release#8565
cknitt wants to merge 13 commits into
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codex/12.3.1

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		- Fix bare labeled arrow types (`~x: int => string`) getting no arity and failing to unify with their parenthesized form. https://github.com/rescript-lang/rescript/pull/8563
		- Fix argument evaluation order when a function call is inlined: the beta reducer could evaluate non-substitutable arguments from last to first. https://github.com/rescript-lang/rescript/pull/8572

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cknitt commented Aug 19, 2026 •

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