feat: ESLint 10 support, flat config only

[retyui]

Summary

Eslint deprecated v9 and v8, only v10 is supported, see: https://eslint.org/version-support/

@callstack/eslint-config v15 doesn't work with ESLint 10. This PR prepares v16.0.0: ESLint 10 support, flat config only, and all dependencies updated to their latest versions.

Breaking changes

• Flat config only. Removed the eslintrc entry points and the *.factory.js helpers. Each config is now a single flat-config file: node.js, react.js, react-native.js.

  • Import paths: @callstack/eslint-config (React Native), @callstack/eslint-config/react, @callstack/eslint-config/node.
  • The v15 *.flat.js paths still work as aliases through the exports map.

• ESLint ^10.0.0 only. ESLint 8 and 9 are dropped.

• Node.js ^22.18.0 || >=24.11.0. Babel 8 requires it.

• eslint-plugin-import → eslint-plugin-import-x. The original has no ESLint 10 support. Rules are renamed from import/* to import-x/*. (Switched to eslint-plugin-import-x due to ESLint 10 compatibility delays and project maintenance friction in eslint-plugin-import#3227.)

• eslint-plugin-flowtype → eslint-plugin-ft-flow. The original is unmaintained and tied to Babel 7. Rules are renamed from flowtype/* to ft-flow/*. (Unmaintained for 5 years in eslint-plugin-flowtype)

• Babel 8 parser. This is the only @babel/eslint-parser release that supports ESLint 10. The project's Babel config is no longer loaded, because React Native's preset is still on Babel 7. JSX and Flow are enabled through parserOpts.plugins instead.

• TypeScript uses parserOptions.projectService: true instead of project: './tsconfig.json'.

Other changes

• eslint-plugin-ft-flow, eslint-plugin-react and eslint-plugin-react-native call context APIs that ESLint 10 removed. They are wrapped with fixupPluginRules from @eslint/compat.
• @eslint/js is now a direct dependency. Previously it resolved only from the test workspace.
• Tests: the ESLint 8 and 9 workspaces are replaced by a single ESLint 10 workspace.
• README rewritten for flat config, with a "Migrating from v15" section.

Test plan

• yarn test passes on ESLint 10.

[retyui]

No official support: Intellicode/eslint-plugin-react-native#333 (comment)

[retyui]

Testing on small project (npx @eslint/config-inspector):

[Copilot]

Copilot review overview

🟡 Changes recommended

Several bundled plugins reject ESLint 10 in their peer ranges, causing strict npm installations to fail.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• eslint-plugin-ft-flow peer range excludes ESLint 10 · New
• Document the exact supported Node.js version range · New

What changed in this PR

Prepares v16 with ESLint 10 support and flat configuration as the sole format.

Changes:

• Consolidates Node, React, and React Native flat configs.
• Upgrades ESLint plugins, parsers, and runtime requirements.
• Replaces legacy test workspaces and updates migration documentation.

File	Description
.github/​workflows/​test.yml	Tests on Node.js 22.
README.md	Documents flat config and migration.
package.json	Defines v16 exports and dependencies.
node.js	Implements the flat Node.js config.
node.flat.js	Removes obsolete flat wrapper.
node.factory.js	Removes legacy config factory.
react.js	Implements the flat React config.
react.flat.js	Removes obsolete flat wrapper.
react.factory.js	Removes legacy config factory.
react-native.js	Implements the flat React Native config.
react-native.flat.js	Removes obsolete flat wrapper.
react-native.factory.js	Removes legacy config factory.
test/​package.json	Targets ESLint 10 and TypeScript 5.9.
test/​index.js	Migrates import rule names.
test/​index.tsx	Migrates TypeScript import rule names.
test/​eslint-v8/​.eslintrc.js	Removes ESLint 8 configuration.
test/​eslint-v8/​package.json	Removes ESLint 8 workspace.
test/​eslint-v9/​package.json	Removes ESLint 9 workspace.
test/​eslint-v10/​package.json	Adds ESLint 10 workspace.
test/​eslint-v10/​eslint.config.mjs	Uses the root package export.
test/​rules/​core.js	Exercises core rules.
test/​rules/​flow.js	Exercises ft-flow rules.
test/​rules/​imports.js	Exercises import-x rules.
test/​rules/​promise.js	Exercises promise rules.
test/​rules/​react.js	Exercises JavaScript React rules.
test/​rules/​react.tsx	Exercises TypeScript React rules.
test/​rules/​react-native.js	Exercises React Native rules.
test/​rules/​react-native.tsx	Exercises typed React Native rules.
test/​rules/​typescript.ts	Exercises TypeScript rules.
test/​rules/​__tests__/​jest.test.js	Exercises JavaScript Jest rules.
test/​rules/​__tests__/​jest.test.ts	Exercises TypeScript Jest rules.

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