[jhuleatt]

Summary

Replaces ESLint 8 and its plugins (@typescript-eslint v5, eslint-plugin-react, eslint-plugin-react-hooks v4, eslint-plugin-no-only-tests) with oxlint, including type-aware linting via oxlint-tsgolint. Also runs npm run lint in the test workflow before the tests.

On main, npm run lint currently fails (a require() in test/setupTests.ts), which is presumably why it wasn't in CI.

Rules

.oxlintrc.json lists rules explicitly. oxlint's categories are turned off, so upgrading oxlint doesn't change what's enforced. It's a rule-by-rule port of the latest recommended presets, keeping this repo's existing warn-level overrides:

• ESLint recommended (minus the rules TypeScript already checks)
• typescript-eslint recommended
• eslint-plugin-react recommended (classic JSX runtime, matching "jsx": "react" in tsconfig)
• eslint-plugin-react-hooks v7 recommended, including the React Compiler rules
• vitest/no-focused-tests instead of eslint-plugin-no-only-tests

Type-aware rules from typescript-eslint's recommended-type-checked:

• no-floating-promises, no-misused-promises, await-thenable, unbound-method, only-throw-error (promises allowed, for Suspense) and the rest of that preset are errors.
• no-redundant-type-constituents, no-unnecessary-type-assertion and restrict-template-expressions have existing findings, so they're warnings for now. They can become errors once those are cleaned up.
• no-deprecated (warning) replaces react/no-deprecated. It flags anything marked @deprecated in its types (e.g. RxJS's toPromise and empty, Vite 8's rollupOptions).
• The no-unsafe-* rules are off. They flag every use of the any values that no-explicit-any already allows as a warning. require-await is off too (stylistic).

Not ported:

• react/prop-types: TypeScript covers it.
• react/jsx-uses-react and react/jsx-uses-vars: oxlint's no-unused-vars already handles JSX.
• no-octal and no-dupe-args: strict mode covers them.
• react/require-render-return and no-useless-assignment: still experimental in oxlint.

Code changes for new findings

• test/setupTests.ts: require → import.
• test/sdk.test.tsx, test/firebaseApp.test.tsx: await deleteApp in afterEach (no-misused-promises).
• src/performance.tsx: suppressed react/static-components with a TODO. SuspenseWithPerf creates its fallback component during render, so React remounts it, and records an extra measure, whenever it re-renders while suspended. Fixing that changes runtime behavior, so it's left for a follow-up.
• Disable comments for one intentional pattern in a test (react/globals) and one false positive (only-throw-error: error is always set when status === 'error').
• test/tsconfig.json (extends tsconfig.test.json): type-aware rules use the nearest tsconfig.json, so without it, test files fell back to defaults (e.g. vi resolved to an error type). Editors pick it up too.
• docs/reference: regenerated for a line number shift.
• CONTRIBUTING.md: npm run lint --fix doesn't pass --fix through; changed it to npm run lint -- --fix.

Results

• npm run lint: 0 errors, 89 warnings, ~0.3s (ESLint took ~2s).
• Lockfile: 98 packages removed, oxlint and oxlint-tsgolint added (plus their platform binaries).
• Locally: tsc (src and tests), the full emulator test suite, npm run docs, and npm ci + lint on Node 22 and 24 all pass.

[tyler-reitz]

Approving. I think switching is the right call for this repo. Speed isn't the reason (under a second vs 1.6s here). The win is getting type-aware rules and the React Compiler hook rules without maintaining an ESLint 9 + typescript-eslint + plugin stack. The tradeoff to watch: type-aware linting runs on oxlint-tsgolint, which is built on TypeScript 7 (typescript-go), while the repo compiles with TypeScript 6.0.3. So lint and tsc can disagree, and tsgolint upgrades follow TS releases. I didn't hit a disagreement here.

On moving to VoidZero tools (now part of Cloudflare): we already depend on Vite 8 (whose bundler, Rolldown, is built on Oxc) and Vitest, so this adds to a dependency we have rather than starting a new one. Switching back would also be cheap, since every rule is listed explicitly under its ESLint name (plugin rules only need a prefix rename).

On the rebased head, lint exits 0 locally and in CI, and both tsc configs are clean. It does catch things: a probe file with .only and an un-awaited promise fails the run with both reported as errors, and misspelled rule names fail it too.

Non-blocking:

• Lint runs in every test matrix leg. If it fails, that leg's tests are skipped.
• The no-unsafe-* rules would add 76 findings, but only 21 in src (the rest are in test/). They could go in as warnings.