Check record labels once per record type

[cknitt]

When the type of a record expression or pattern isn't known from context, the type checker narrows the candidate labels for each field using the record's other fields (Typecore.disambiguate_label_by_ids). For every field and every candidate, it built a hash table of all the labels of the candidate's record type and looked up every field name in it. That is quadratic in the number of fields.

Whether a candidate fits only depends on its record type (the lbl_all array its labels share), so the checks are now done once per record type for the whole expression or pattern.

Untyped record with 2,400 fields	Before	After
Record literal	1.1s	127ms
Record pattern	1.18s	208ms

Record patterns still grow somewhat faster than linearly; the remaining cost is in the pattern-match checks, not in label disambiguation.

No generated output or error message changes.

🤖 Generated with Claude Code

[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

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

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-11T19:43:33.410330Z	819a9a4	Manual request

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.58%. Comparing base (f30bea4) to head (3296593).

Files with missing lines	Patch %	Lines
compiler/ml/typecore.ml	94.11%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8799   +/-   ##
=======================================
  Coverage   80.58%   80.58%           
=======================================
  Files         447      447           
  Lines       61681    61689    +8     
=======================================
+ Hits        49704    49712    +8     
  Misses      11977    11977           

Files with missing lines	Coverage Δ
compiler/ml/typecore.ml	86.50% <94.11%> (+0.04%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pkg-pr-new]

Open in StackBlitz

rescript

npm i https://pkg.pr.new/rescript@8799

@rescript/belt

npm i https://pkg.pr.new/@rescript/belt@8799

@rescript/darwin-arm64

npm i https://pkg.pr.new/@rescript/darwin-arm64@8799

@rescript/darwin-x64

npm i https://pkg.pr.new/@rescript/darwin-x64@8799

@rescript/linux-arm64

npm i https://pkg.pr.new/@rescript/linux-arm64@8799

@rescript/linux-x64

npm i https://pkg.pr.new/@rescript/linux-x64@8799

@rescript/runtime

npm i https://pkg.pr.new/@rescript/runtime@8799

@rescript/win32-x64

npm i https://pkg.pr.new/@rescript/win32-x64@8799

commit: 3296593

[chatgpt-codex-connector]

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

Reviewed commit: 819a9a488f

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[github-actions]

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8799