feat: bound what the TypeScript check's worker may hold with memoryLimit by alexander-akait · Pull Request #386 · webpack/diagnostics-webpack-plugin

alexander-akait · 2026-10-23T13:37:38Z

Part of the performance series (#376–#385). This one bounds memory rather than saving it.

Problem

The TypeScript check's worker thread could hold as much heap as Node gives a thread, and nothing capped it. fork-ts-checker-webpack-plugin sets a memoryLimit (default 2048 MB, as --max-old-space-size on its process), and ts-checker-rspack-plugin defaults to 8192 MB.

Change

New option, memoryLimit (MB, minimum 16). It's handed to the worker as resourceLimits.maxOldGenerationSizeMb; jest-worker 30.5 forwards it.
What happens past the limit: jest-worker rejects the run with "Jest worker ran out of memory and crashed", and webpack's process carries on. The check then:
- reports the limit: "ran out of the N MB of memory memoryLimit lets its worker hold: raise it, or set skipLibCheck to check less";
- drops the worker, so the next build starts the program from nothing.
Why 16 is the minimum: at 1 MB, V8 can't even start the thread's isolate ("Fatal JavaScript out of memory: GC during deserialization") and ends the whole process. 16 MB fails gracefully.
Default: unset, so behaviour is as before.
README section, options-table entry, schema (validators regenerated), changeset and types are updated.

Measured

301 files, TypeScript check on its worker, one-shot:

`memoryLimit`	wall	CPU	peak RSS	result
unset	4.05 s	10.8 s	588 MB	clean
512	4.43 s	11.2 s	555 MB	clean
256	4.80 s	12.4 s	570 MB	clean
160	4.62 s	13.5 s	474 MB	reports the limit

Near the limit the collector works harder, so this is for keeping a runaway program from taking the build down, not for speed. The README says so.

Tests

New (in test/typescript/threads.test.js): with memoryLimit: 16, the check reports the limit, and the next build without it reports the usual TS2322. With the option not handed to the worker, this test fails. It's skipped where there's no thread to spare, since the check then runs on webpack's thread, which the limit isn't for.
Full suite: 315/315, global module path cleared, as on CI. eslint, tsc, prettier, cspell and lint:schema are clean.

Generated by Claude Code

Summary by CodeRabbit

New Features
- TypeScript checks now support an optional worker memory limit, specified in megabytes. The minimum allowed value is 16 MB; without a limit, the worker may use as much memory as Node.js allows.
Bug Fixes
- When a TypeScript check exceeds its worker’s memory limit, the issue is reported and the worker starts from scratch on the next build.
- Memory-limit errors now indicate whether a custom limit was set and suggest ways to address the issue.
Documentation
- Added guidance on configuring the memory limit and its behavior.

The worker a TypeScript check runs on held as much as Node gives a thread, and a runaway program had nothing to stop it short of that. `memoryLimit` (MB, at least 16) is handed to the worker as `maxOldGenerationSizeMb`. Over it, jest-worker rejects the run; the check reports the limit, drops the worker, and the next build starts the program from nothing. Below 16 MB V8 cannot start the thread at all and ends the process, hence the minimum. It bounds memory rather than saving it: 301 files peaked at 588 MB without a limit, 555 MB under 512 MB at +10% time, and ran out under 160 MB, as reported. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

linux-foundation-easycla · 2026-10-23T13:37:45Z

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codecov · 2026-10-23T13:45:00Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.64%. Comparing base (dc3ff2f) to head (80e2f61).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #386      +/-   ##
==========================================
+ Coverage   99.62%   99.64%   +0.01%     
==========================================
  Files          19       19              
  Lines        5400     5649     +249     
==========================================
+ Hits         5380     5629     +249     
  Misses         20       20

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coderabbitai · 2026-10-23T13:45:07Z

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.changeset/ts-memory-limit.md
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Walkthrough

The TypeScript check now accepts an optional worker memory limit in megabytes, with a minimum of 16. The checker passes the limit to the worker’s heap configuration. After worker errors, the checker removes and ends the worker; memory-exhaustion errors receive a specific message that retains the original error as its cause. The README and changeset describe the option, and a test covers limited and unrestricted worker runs.

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to f2a9e

The memory limit may not provide the protection described, particularly when Node starts with an explicit heap flag. Clarify these limitations before merge or accept the bounded documentation risk.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 5 files. (3 skipped: 3…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the main change: adding a memoryLimit option to bound the TypeScript check worker's memory usage.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 5 files. (3 skipped: 3 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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.changeset/ts-memory-limit.md
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types/threads.d.ts

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

alexander-akait · 2026-10-23T13:58:24Z

EasyCLA fails because the commits carry a Co-Authored-By: Claude trailer that maps to no GitHub account. It is not a code failure. Whether to drop the trailer or accept the check is for the maintainers to decide, so I haven't rewritten history.

Generated by Claude Code

alexander-akait mentioned this pull request Oct 23, 2026

perf: hand Biome and oxlint every file at once #387

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coderabbitai Bot reviewed Oct 23, 2026

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Comment thread README.md Outdated

Comment thread src/threads.js

docs: say memoryLimit bounds the worker's heap, and what overrides it

80e2f61

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

alexander-akait closed this Oct 23, 2026

alexander-akait mentioned this pull request Oct 23, 2026

feat: TypeScript 7.1 support, one place for compiler-lived state, shared TypeScript runs #392

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feat: bound what the TypeScript check's worker may hold with memoryLimit - #386

feat: bound what the TypeScript check's worker may hold with memoryLimit#386
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