fix(linter/plugins): patch `WeakMap` to emulate `WeakMap`s keyed by `sourceCode` by overlookmotel · Pull Request #20799 · oxc-project/oxc

overlookmotel · 2026-03-27T13:21:02Z

Fixes #20700.

Patch global WeakMap before loading plugins to make a WeakMap keyed by context.sourceCode act as if every file has a unique context.sourceCode.

The runtime cost of this patch is very low - for the use case of WeakMap keyed by SourceCode, it should be faster than an actual WeakMap, as no methods do actual hash map lookups. The implementation takes care not to leak memory even if plugins use WeakMaps extensively or in pathological patterns.

I rebased #20611 on top of this, and after this PR, 100% of eslint-plugin-mocha's conformance tests pass.

It's pretty hacky to be patching globals, but I believe the implementation to be robust. My rationale for this solution is explained in detail in #20700.

overlookmotel · 2026-03-27T13:21:16Z

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overlookmotel · 2026-03-27T13:40:05Z

@camc314 Are you happy with this solution?

Copilot

Pull request overview

This PR patches the JS plugins runtime to emulate ESLint’s per-file context.sourceCode identity for plugin caches that use WeakMap<SourceCode, …>, fixing cross-file state leakage caused by Oxlint’s singleton SOURCE_CODE.

Changes:

Patch globalThis.WeakMap in the plugins runtime and add resetWeakMaps() to clear SOURCE_CODE-keyed entries between files.
Ensure the patch is applied before plugins load; call resetWeakMaps() as part of per-file teardown.
Add unit + e2e fixture coverage, and split Vitest into normal vs isolated projects to contain global side effects.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
apps/oxlint/vitest.config.ts	Splits test run into “tests” and “isolated” projects to contain global `WeakMap` patch side effects.
apps/oxlint/test/weak_map.isolated.test.ts	Unit tests for patched `WeakMap` behavior + `resetWeakMaps()`.
apps/oxlint/test/fixtures/weakMaps/plugin.ts	Fixture plugin that reproduces `WeakMap`-keyed-by-`sourceCode` caching pattern across multiple rules.
apps/oxlint/test/fixtures/weakMaps/output.snap.md	Oxlint CLI snapshot asserting per-file isolation across multiple files.
apps/oxlint/test/fixtures/weakMaps/options.json	Enables ESLint snapshot generation for the fixture.
apps/oxlint/test/fixtures/weakMaps/files/1.js	Fixture input file 1.
apps/oxlint/test/fixtures/weakMaps/files/2.js	Fixture input file 2.
apps/oxlint/test/fixtures/weakMaps/files/3.js	Fixture input file 3.
apps/oxlint/test/fixtures/weakMaps/eslint.snap.md	ESLint output snapshot for parity with fixture expectations.
apps/oxlint/test/fixtures/weakMaps/eslint.config.js	ESLint config to run the fixture plugin.
apps/oxlint/test/fixtures/weakMaps/.oxlintrc.json	Oxlint config to load the fixture plugin via `jsPlugins`.
apps/oxlint/src-js/plugins/weak_map.ts	Implements the global `WeakMap` patch + tracking/reset logic.
apps/oxlint/src-js/plugins/lint.ts	Calls `resetWeakMaps()` during per-file reset.
apps/oxlint/src-js/plugins/index.ts	Ensures the `WeakMap` patch is applied before loading plugins.

apps/oxlint/src-js/plugins/weak_map.ts

camc314 · 2026-03-27T14:08:34Z

@camc314 Are you happy with this solution?

I haven't looked at the code, but from the PR title + description, i think this is a reasonable approach to fix the problem - nice work!

overlookmotel · 2026-03-27T15:11:17Z

Thanks for taking a look. Let's merge it and see what happens!

overlookmotel · 2026-03-27T15:12:23Z

Merge activity

Mar 27, 3:12 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Mar 27, 3:12 PM UTC: overlookmotel added this pull request to the Graphite merge queue.
Mar 27, 3:16 PM UTC: Merged by the Graphite merge queue.

…sourceCode` (#20799) Fixes #20700. Patch global `WeakMap` before loading plugins to make a `WeakMap` keyed by `context.sourceCode` act as if every file has a unique `context.sourceCode`. The runtime cost of this patch is very low - for the use case of `WeakMap` keyed by `SourceCode`, it should be *faster* than an actual `WeakMap`, as no methods do actual hash map lookups. The implementation takes care not to leak memory even if plugins use `WeakMap`s extensively or in pathological patterns. I rebased #20611 on top of this, and after this PR, 100% of `eslint-plugin-mocha`'s conformance tests pass. It's pretty hacky to be patching globals, but I believe the implementation to be robust. My rationale for this solution is explained in detail in #20700.

# Oxlint ### 💥 BREAKING CHANGES - c0ebbce linter: [**BREAKING**] Report error on unknown builtin rule (#20464) (camc314) ### 🚀 Features - 04f85e5 linter/no-unused-vars: Add safe-fix option for import fixes (#20839) (Marcell Toth) - 32a3706 linter/eslint-vitest-plugin: Implements `require-test-timeout` rule (#20806) (Said Atrahouch) - ae03653 linter: Implement suggestion for `eslint/no-useless-computed-key` rule (#20805) (Mikhail Baev) - 6624513 linter/prefer-string-starts-ends-with: Move rule from nursery to style (#20797) (camc314) - 58941f8 linter/prefer-readonly: Move rule from nursery to style (#20796) (camc314) - 8837ffd linter/prefer-regexp-exec: Move rule from nursery to style (#20795) (camc314) - 7e88871 linter/prefer-find: Move rule out of nursery (#20794) (camc314) - ca6e5bc linter/vitest: Implement prefer-called-exactly-once-with (#17562) (Said Atrahouch) - e80c0bf linter/eslint-plugin-vitest: Implement `require-mock-type-parameters` (#20785) (Said Atrahouch) - cec8b8f linter/vitest: Implement require-awaited-expect-poll rule (#20702) (Said Atrahouch) - d8e9d01 linter/eslint-plugin-vitest: Set `prefer-to-have-been-called-times` compatible with jest (#20703) (Said Atrahouch) - caf8231 linter: Enhance import plugin diagnostics with help messages (#20766) (离谱) - f44adfa linter: Improve the oxlint config generated by `--init`. (#20632) (connorshea) - 43f4827 linter: Add help text to jest and promise diagnostics (#20640) (kszongic) - 16516de linter: Enhance types for `DummyRule` (#20751) (camc314) - 27374e8 linter: Add hint about node version when ts config fail to import (#20570) (camc314) - 8e34150 linter/eslint-plugin-vitest: Sync rule with JS implementation (#20679) (Said Atrahouch) ### 🐛 Bug Fixes - df057d5 linter/no-noninteractive-tabindex: Add missing composite widget … (#20860) (bab) - bb34073 linter: Mark vitest/valid-title as a compatible jest rules (#20463) (Nicolas Le Cam) - bd2c76b linter: Handle shadowed locals in no-restricted-globals (#20811) (Ulrich Stark) - 62e39be linter: Sort nested object keys in fix of `eslint/sort-keys` in one pass (#20838) (Ulrich Stark) - 3ef37da oxlint/lsp: Error on unknown command (#20841) (Sysix) - ab1070d oxlint/cli: Skip parsing base config again for nested config search (#20809) (Sysix) - 2be3728 oxlint/lsp: Skip parsing base config again for nested config search (#20808) (Sysix) - 6171217 oxlint: Respect `NO_COLOR` env for `format=stylish` (#20804) (Sysix) - d89ae8f linter/plugins: Patch `WeakMap` to emulate `WeakMap`s keyed by `sourceCode` (#20799) (overlookmotel) - c610666 linter/no-shadow: Respect env settings when builtinGlobals is enabled (#20429) (vvnikita74) - 6bb502f linter/no-invalid-void-type: Allow void generic args in heritage clauses (#20780) (camc314) - 365bb7d linter: Skip typed nested literals in explicit-module-boundary-types (#20776) (camc314) - 0aa1ff0 linter/plugins: Ensure `after` hook is always called in ESLint compat mode (#20721) (overlookmotel) - 31145a9 linter/plugins: Fire `after` hook after CFG events in ESLint compat (#20720) (overlookmotel) - c09a5ab diagnostics: Skip minified fallback for single-line reporters (#20716) (camc314) - e4dc9a1 linter: Isolate `--init` config writes from parallel tests (#20717) (camc314) - 7e394ec linter: Clarify empty replacement fixer help text (#20698) (camc314) - d15a99c linter/jsx-curly-brace-presence: Flag empty string literals (#20690) (camc314) ### 📚 Documentation - c722495 linter: Update JS Plugins + LS references (#20843) (camc314) - e1f9748 linter/jsdoc/require-property: Fix typo (#20792) (Benjaming61001) - be3dcc1 linter: Add note about node version + custom TS plugin (#19381) (camc314) # Oxfmt ### 🚀 Features - 6ef440a oxfmt: Support bool for object style options (#20853) (leaysgur) - 23050fa oxfmt: Support markdown-in-js substitution (#20683) (leaysgur) - 4087295 oxfmt: Support angular-in-js substitution (#20676) (leaysgur)

github-actions bot added A-linter Area - Linter A-cli Area - CLI A-linter-plugins Area - Linter JS plugins C-bug Category - Bug labels Mar 27, 2026

overlookmotel mentioned this pull request Mar 27, 2026

Linter plugins: Add APIs to support sharing per-file data between rules #20700

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overlookmotel marked this pull request as ready for review March 27, 2026 13:37

overlookmotel requested a review from camc314 as a code owner March 27, 2026 13:37

Copilot AI review requested due to automatic review settings March 27, 2026 13:37

Copilot started reviewing on behalf of overlookmotel March 27, 2026 13:38 View session

overlookmotel assigned camc314 Mar 27, 2026

Copilot AI reviewed Mar 27, 2026

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apps/oxlint/src-js/plugins/weak_map.ts Show resolved Hide resolved

overlookmotel force-pushed the om/03-26-fix_linter_plugins_patch_weakmap_to_emulate_weakmap_s_keyed_by_sourcecode_ branch from 70411e6 to be32d12 Compare March 27, 2026 13:53

overlookmotel mentioned this pull request Mar 27, 2026

test(linter/plugins): Add eslint-plugin-mocha to JS Plugins conformance suite #20611

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overlookmotel assigned overlookmotel and unassigned camc314 Mar 27, 2026

overlookmotel added the 0-merge Merge with Graphite Merge Queue label Mar 27, 2026

graphite-app bot force-pushed the om/03-26-fix_linter_plugins_patch_weakmap_to_emulate_weakmap_s_keyed_by_sourcecode_ branch from be32d12 to d89ae8f Compare March 27, 2026 15:13

graphite-app bot merged commit d89ae8f into main Mar 27, 2026
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graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Mar 27, 2026

graphite-app bot deleted the om/03-26-fix_linter_plugins_patch_weakmap_to_emulate_weakmap_s_keyed_by_sourcecode_ branch March 27, 2026 15:16

Boshen mentioned this pull request Mar 30, 2026

release(apps): oxlint v1.58.0 && oxfmt v0.43.0 #20867

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fix(linter/plugins): patch `WeakMap` to emulate `WeakMap`s keyed by `sourceCode`#20799

fix(linter/plugins): patch `WeakMap` to emulate `WeakMap`s keyed by `sourceCode`#20799
graphite-app[bot] merged 1 commit intomainfrom
om/03-26-fix_linter_plugins_patch_weakmap_to_emulate_weakmap_s_keyed_by_sourcecode_

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