Upgrade ESLint 9 → 10 (breaking changes)

[Blb3D]

Context

Dependabot PR #272 attempted to bump @eslint/js from 9.x to 10.x, but CI fails — frontend lint/build breaks.

Breaking Changes in ESLint 10

• Node.js >= 20.19 required
• Config file lookup changed: starts from linted file directory, not CWD
• JSX elements treated as references: no-unused-vars may flag new issues with component imports
• Legacy .eslintrc completely removed (we already use flat config — OK)
• Deprecated context methods removed (affects custom rules/plugins)

Required Changes

1. Bump eslint from ^9.x to ^10.x
2. Bump @eslint/js to ^10.x
3. Verify Node.js version in CI >= 20.19
4. Verify plugin compatibility: eslint-plugin-react-hooks, eslint-plugin-react-refresh, eslint-plugin-storybook
5. Run npm run lint and fix any new errors from JSX reference tracking
6. Test config file lookup behavior in monorepo structure

References

• ESLint 10 migration guide
• Closed PR: deps(js): bump @eslint/js from 9.39.2 to 10.0.1 in /frontend #272

[Blb3D]

Blocked by eslint-plugin-react-hooks

Investigated this upgrade — eslint-plugin-react-hooks@7.0.1 (current) has peerDependencies.eslint: "^3.0.0 || ... || ^9.0.0" and does not support ESLint 10.

Even the latest canary (7.1.0-canary-ed4bd540-20260202) still caps at ^9.0.0.

This upgrade is blocked until the React team publishes a version of eslint-plugin-react-hooks that supports ESLint 10. We could use --legacy-peer-deps to force it, but that risks subtle breakage and isn't worth it for a lint tool.

Leaving this issue open to revisit once the plugin is updated.

[Blb3D]

Status Update (March 2026)

The blocker has been partially resolved. The PR adding ESLint 10 support to eslint-plugin-react-hooks was merged on Feb 13, 2026.

Current state:

• Canary eslint-plugin-react-hooks@7.1.0-canary-e8c63626-20260213 includes ^10.0.0 in peerDependencies ✅
• No stable release yet — latest stable is still 7.0.1 with ^9.0.0 only
• Pinning a canary for a lint tool is fragile and not recommended

Recommendation: Keep deferred until React team publishes stable 7.1.0 (or 8.0.0) with ESLint 10 support. Once available, the upgrade should be straightforward since we already use flat config.

To check for a new release:

npm view eslint-plugin-react-hooks peerDependencies

When this shows ^10.0.0, we're clear to upgrade.

[Blb3D]

Triage (2026-03-30): Still blocked by upstream.

Current: eslint@^9.39.4. Blocker: eslint-plugin-react-hooks (React team's official plugin) only supports ESLint ^3-^9. Already documented in DEFERRED_UPGRADES.md.

No action until React team ships ESLint 10 support for the hooks plugin.