Add opt-in cross-module inlining for Option helpers by cknitt · Pull Request #8689 · rescript-lang/rescript

cknitt · 2026-09-28T07:49:25Z

Add @inline(crossModule) to opt individual functions into cross-module inlining, and use it for selected Option helpers.

Inlining copies a function’s body into its callers. If that body changes but its type does not, the caller must still be rebuilt; checking only the .cmi type signature would leave the old body in the generated JavaScript.

The compiler stores exported inline bodies in the existing .cmj file, alongside other JavaScript compilation metadata. Rewatch now compares the digest already stored in that file’s header before and after compiling a module. If it changes, Rewatch rebuilds dependents. This keeps implementation details out of .cmi and requires no new artifact. A .cmj change unrelated to inlining may also cause a dependent rebuild.

codecov · 2026-09-28T08:10:27Z

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.44%. Comparing base (1a49d91) to head (08056a9).

Files with missing lines	Patch %	Lines
compiler/core/lam_stats_export.ml	66.66%	2 Missing ⚠️
compiler/ml/translattribute.ml	33.33%	2 Missing ⚠️
compiler/core/lam_analysis.ml	0.00%	1 Missing ⚠️
compiler/ml/printlambda.ml	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8689      +/-   ##
==========================================
+ Coverage   81.42%   81.44%   +0.02%     
==========================================
  Files         459      459              
  Lines       64547    64554       +7     
==========================================
+ Hits        52559    52578      +19     
+ Misses      11988    11976      -12

Files with missing lines	Coverage Δ
compiler/core/js_cmj_format.ml	`92.98% <100.00%> (+0.12%)`	⬆️
compiler/ml/lambda.ml	`70.86% <ø> (ø)`
compiler/core/lam_analysis.ml	`78.23% <0.00%> (-0.69%)`	⬇️
compiler/ml/printlambda.ml	`8.81% <0.00%> (-0.04%)`	⬇️
compiler/core/lam_stats_export.ml	`88.23% <66.66%> (-2.88%)`	⬇️
compiler/ml/translattribute.ml	`75.55% <33.33%> (+1.64%)`	⬆️

... and 6 files with indirect coverage changes

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pkg-pr-new · 2026-09-28T08:22:06Z

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commit: 08056a9

github-actions · 2026-09-28T08:24:29Z

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8689

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chatgpt-codex-connector · 2026-09-28T10:09:40Z

+          else if not (Lam_closure.is_closed lambda) then
+            Location.raise_errorf ~loc
+              "@inline(crossModule) requires a function without captured local \
+               values"


Treat catch binders as local during inline validation

For an exported @inline(crossModule) function containing a try ... catch whose handler inspects the exception, this check incorrectly rejects the function as capturing a local value. Lam_closure.is_closed delegates to free_variables, but its Ltrywith branch ignores _exn instead of adding that binder to the local set (compiler/core/lam_closure.ml:118-120), so ordinary references to the caught exception are reported as free. Register the catch binder during closure traversal or use validation that handles all Lambda binders.

AGENTS.md reference: AGENTS.md:L51-L54

Useful? React with 👍 / 👎.

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

Why: The OCaml build system, now the default `rescript`, recompiled dependents only when a module's CMI changed. An `@inline(crossModule)` body lives in the CMJ and can change while the CMI stays the same, so callers kept the old inlined code, during a build and on the next build after the dependency was compiled separately. Rust rewatch already compares CMJ digests since the previous commits. Publishing a byte-different CMJ now marks dependents dirty like a changed CMI, and the startup freshness check compares a dependent's CMT with the later of its dependency's CMI and CMJ. Review: Does every implementation change now recompile dependents? Only those whose CMJ bytes change, matching the Rust implementation. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gKsWykY6KH4QSJ9Wrs Signed-off-by: Christoph Knittel <ck@cca.io>

github-actions · 2026-10-27T10:35:50Z

Changelog

🚀 New Feature

Allow selected functions to opt into cross-module inlining with @inline(crossModule) and inline common Option helpers in application code.

Semantic Diff

7 commits · Full page

Enable selective cross-module inlining for Option helpers

_{00d6bff · cknitt · Sep 28, 2026, 06:04 UTC}

Inline additional Option helpers across modules

_{3da43ad · cknitt · Sep 28, 2026, 07:46 UTC}

Document cross-module inlining feature

_{cb4faed · cknitt · Sep 28, 2026, 07:49 UTC}

Refresh Option inlining snapshots after clean build

_{0e010a0 · cknitt · Sep 28, 2026, 07:55 UTC}

Track CMJ changes for cross-module inlining

_{a7681f8 · cknitt · Sep 28, 2026, 09:19 UTC}

Read CMJ digest header for incremental rebuilds

_{7ce5284 · cknitt · Sep 28, 2026, 09:53 UTC}

✨ Recompile dependents of a changed CMJ in the OCaml build system

_{08056a9 · cknitt + Claude · Oct 27, 2026, 07:15 UTC · new}

Why

The OCaml build system, now the default rescript, recompiled dependents only when a module's CMI changed. An @inline(crossModule) body lives in the CMJ and can change while the CMI stays the same, so callers kept the old inlined code, during a build and on the next build after the dependency was compiled separately. Rust rewatch already compares CMJ digests since the previous commits.

Publishing a byte-different CMJ now marks dependents dirty like a changed CMI, and the startup freshness check compares a dependent's CMT with the later of its dependency's CMI and CMJ.

Review

Does every implementation change now recompile dependents? Only those whose CMJ bytes change, matching the Rust implementation.

cknitt marked this pull request as ready for review September 28, 2026 10:04

chatgpt-codex-connector Bot reviewed Sep 28, 2026

View reviewed changes

cknitt mentioned this pull request Oct 7, 2026

Inlining in the compiler: current state and proposed changes #8733

Open

cknitt and others added 7 commits October 27, 2026 06:42

Enable selective cross-module inlining for Option helpers

00d6bff

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

Inline additional Option helpers across modules

3da43ad

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

Document cross-module inlining feature

cb4faed

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

Refresh Option inlining snapshots after clean build

0e010a0

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

Track CMJ changes for cross-module inlining

a7681f8

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

Read CMJ digest header for incremental rebuilds

7ce5284

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

cknitt force-pushed the codex/cross-module-inline branch from 24646c5 to 08056a9 Compare October 27, 2026 10:35

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Add opt-in cross-module inlining for Option helpers - #8689

Add opt-in cross-module inlining for Option helpers#8689
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