Drop unread data from .cmt files by cknitt · Pull Request #9252 · rescript-lang/rescript

cknitt · 2026-11-06T21:27:34Z

Drops data that no tool reads from .cmt/.cmti files. Follow-up to the artifact-size findings in #9148.

Value dependencies as two locations and a flag. Each value inclusion check stored both full Types.value_descriptions (type, attributes, doc comments). Reanalyze, the only reader, uses the two locations and whether both types take optional arguments, so that's all the compiler records now. The flag is decided when the .cmt is written, as before, when the types were marshalled at that point.
Unread cmt_infos fields removed. cmt_comments (always empty), cmt_args, cmt_sourcefile, cmt_builddir, cmt_loadpath, cmt_initial_env, cmt_imports and cmt_use_summaries were write-only. The OCAML_BINANNOT_WITHENV switch is removed as well. What's left: module name, typed tree, value dependencies, source digest (rescript-tools migrate) and deprecation uses.
Env.summary removed. Every env extension prepended a summary node, and .cmt files kept these logs in every typed-tree environment. OCaml tools replay them through Envaux, which this compiler doesn't have. The envs stored in .cmt files now keep only their GADT local constraints and flags. Reanalyze and gentype only look things up in those envs, and those lookups read tables that were already empty in .cmt files.

Runtime artifacts, master → this PR:

	master	PR	change
`.cmt` total	4.07 MB	3.05 MB	−25%
`.cmti` total	1.24 MB	1.12 MB	−9%
`Stdlib_Array.cmt`	195 KB	102 KB	−48%

.cmi files are unchanged. On 54 Belt and tests/tests files, the generated JS is byte-identical and allocation is 0.2% lower.

No magic-number bump, per compiler/AGENTS.md.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kbf3gLMbg8G3FeSq6sPLM2

Why: Each value inclusion check stored both full value descriptions (type, attributes, doc comments) in the .cmt, a fifth of the stdlib's .cmt bytes. Reanalyze, the only reader, uses the two locations and whether both types take optional arguments; the compiler now records just that. Review: Does reanalyze still see the same optional-argument references? Yes: the flag is computed with the same check on the same two types, the deadcode snapshots are unchanged, and forcing the flag off adds three findings to them. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gLMbg8G3FeSq6sPLM2 Signed-off-by: Christoph Knittel <ck@cca.io>

Why: Eight cmt_infos fields came from OCaml and had no reader: the comments (always empty), the command line, source file, build directory, load path, initial environment, imports and the use_summaries flag. Dropping them and the OCAML_BINANNOT_WITHENV switch (which kept full environments in the typed tree) leaves the module name, the typed tree, the value dependencies, the source digest (rescript-tools migrate) and the deprecation uses. The runtime's .cmt and .cmti files get 3% smaller. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gLMbg8G3FeSq6sPLM2 Signed-off-by: Christoph Knittel <ck@cca.io>

Why: Every environment extension also prepended a summary node (a log of the bindings and opens that built it), and .cmt files kept these logs in every environment of the typed tree. OCaml tools replay them with Envaux to rebuild an environment; this compiler has no Envaux and no tool reads them. The environments stored in .cmt files now keep only their GADT local constraints and flags, and the runtime's .cmt and .cmti files get 7% smaller. Review: Do reanalyze and gentype lose anything? No: they only look types and modules up in typed-tree environments, and the tables those lookups read were already empty in .cmt files. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gLMbg8G3FeSq6sPLM2 Signed-off-by: Christoph Knittel <ck@cca.io>

github-actions · 2026-11-06T21:27:59Z

Changelog

🏠 Internal

Write a quarter less into .cmt files by dropping data no tool reads (full value descriptions in the value dependencies, OCaml-only fields, environment summaries).

Semantic Diff

3 commits · Full page

Record value dependencies in .cmt files as two locations and a flag

_{bc2f41b · cknitt + Claude · Nov 06, 2026, 21:06 UTC}

Why

Each value inclusion check stored both full value descriptions (type, attributes, doc comments) in the .cmt, a fifth of the stdlib's .cmt bytes. Reanalyze, the only reader, uses the two locations and whether both types take optional arguments; the compiler now records just that.

Review

Does reanalyze still see the same optional-argument references? Yes: the flag is computed with the same check on the same two types, the deadcode snapshots are unchanged, and forcing the flag off adds three findings to them.

Stop writing .cmt fields that no tool reads

_{5a289d9 · cknitt + Claude · Nov 06, 2026, 21:10 UTC}

Why

Eight cmt_infos fields came from OCaml and had no reader: the comments (always empty), the command line, source file, build directory, load path, initial environment, imports and the use_summaries flag. Dropping them and the OCAML_BINANNOT_WITHENV switch (which kept full environments in the typed tree) leaves the module name, the typed tree, the value dependencies, the source digest (rescript-tools migrate) and the deprecation uses. The runtime's .cmt and .cmti files get 3% smaller.

Remove environment summaries

_{14fa937 · cknitt + Claude · Nov 06, 2026, 21:12 UTC}

Why

Every environment extension also prepended a summary node (a log of the bindings and opens that built it), and .cmt files kept these logs in every environment of the typed tree. OCaml tools replay them with Envaux to rebuild an environment; this compiler has no Envaux and no tool reads them. The environments stored in .cmt files now keep only their GADT local constraints and flags, and the runtime's .cmt and .cmti files get 7% smaller.

Review

Do reanalyze and gentype lose anything? No: they only look types and modules up in typed-tree environments, and the tables those lookups read were already empty in .cmt files.

codecov · 2026-11-06T21:33:05Z

Codecov Report

❌ Patch coverage is 94.11765% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.74%. Comparing base (827be16) to head (14fa937).

Files with missing lines	Patch %	Lines
compiler/ml/cmt_format_common.ml	89.47%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9252   +/-   ##
=======================================
  Coverage   81.74%   81.74%           
=======================================
  Files         457      457           
  Lines       65713    65708    -5     
=======================================
- Hits        53715    53711    -4     
+ Misses      11998    11997    -1

Files with missing lines	Coverage Δ
analysis/reanalyze/src/dead_optional_args.ml	`92.00% <100.00%> (ø)`
analysis/reanalyze/src/dead_value.ml	`85.95% <100.00%> (+0.06%)`	⬆️
compiler/bsc/rescript_compiler_driver.ml	`80.70% <ø> (-0.07%)`	⬇️
compiler/core/js_implementation.ml	`83.89% <100.00%> (ø)`
compiler/ext/compiler_request_state.ml	`93.75% <ø> (ø)`
compiler/ml/cmt_format.ml	`100.00% <100.00%> (ø)`
compiler/ml/env.ml	`79.27% <100.00%> (-0.10%)`	⬇️
compiler/ml/typemod.ml	`76.90% <ø> (ø)`
tests/ounit_tests/ounit_compiler_request_tests.ml	`97.07% <100.00%> (-0.02%)`	⬇️
compiler/ml/cmt_format_common.ml	`85.00% <89.47%> (+3.51%)`	⬆️

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pkg-pr-new · 2026-11-06T21:37:08Z

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commit: 14fa937

github-actions · 2026-11-06T21:40:43Z

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-9252

cknitt · 2026-11-07T06:04:09Z

@codex review

chatgpt-codex-connector · 2026-11-07T06:04:31Z

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-07T06:05:46.722468Z	`14fa937`	Manual request

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chatgpt-codex-connector · 2026-11-07T06:05:45Z

Codex Review: Didn't find any major issues. Swish!

Reviewed commit: 14fa937d67

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cknitt and others added 3 commits November 6, 2026 21:26

cknitt marked this pull request as ready for review November 7, 2026 06:17

cknitt requested a review from cristianoc November 7, 2026 06:18

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Drop unread data from .cmt files - #9252

Drop unread data from .cmt files#9252
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