Enable Strict TS API by default (#57490)

[huntie]

Summary:

See RFC0894: Removing deep imports from react-native

This is the big switch to enable the Strict TypeScript API (generated types + single index entry point) by default in React Native.

Opt-in → opt-out

After this change, the main react-native package resolves its "types" entry points only to types_generated/index.d.ts — with no other subpaths available.

The new "react-native-legacy-deep-imports" condition maps to legacy types/ and Libraries/*.d.ts sources.

Impact limitation: For this stage of rollout, the "default" condition continues to resolve to source files. Only TypeScript is affected.

How to opt out

Opposite of today's opt-in, which we will update in the docs. Again, the only impact area today is TypeScript.

// tsconfig.json
{
  "extends": "@react-native/typescript-config",
  "compilerOptions": {
    ...
    "customConditions": ["react-native-legacy-deep-imports"]
  }
}

Other changes

• Drop @react-native/typescript-config/strict entry point, update README.
• Update __typetests__.

Rollout plan

Target release: 0.87. This and the contributing stack will be cherry picked for RC1.

• We've conducted testing against 100+ real Expo codebases, giving us the confidence that we've reduced breaking changes enough that the vast majority of RN codebases can migrate.
• The Strict API includes a number of intentional breaking changes, and docs have been kept up to date.
• We're shipping a /migrate-to-strict-api skill to migrate via agents, see Add migrate-to-strict-api skill react-native-community/skills#3.

What's improved since 0.80?

Since the initial opt-in launch of the Strict API in 0.80, we've been making continuous improvements over the last year to get our generated types into a widely launchable state.

Most notably:

• 21+ new/updated root APIs and fixes due to community feedback (discussion, PRs).
• Upstream encapsulation blocker in TypeScript, fixed in 6.0 (Enabling "Strict TypeScript API" doesn't restrict access to react-native/Libraries/* #53565).
• Tailwind/Uniwind compatibility (interface types for props).
• *Instance ref type exports for all built-in components (RFC: Add dedicated Instance types for built-in component refs (JS API stabilization) react-native-community/discussions-and-proposals#1003).
• Fixes to previously mistyped, high impact APIs, such as Appearance.
• New subpath entry points for asset-registry, setup-env, and others.
• Refinements to doc comments/type translation build.

Rollback plan

Revert this diff.

IMPORTANT: We'll adopt a policy of super-eager rollback, if there are any unsolvable issues during the RC phase.

Changelog:
[General][Breaking] - React Native's default JavaScript API is now the Strict TypeScript API. Use customConditions: ["react-native-legacy-deep-imports"] to opt out.

Reviewed By: cortinico

Differential Revision: D110458670

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@huntie has exported this pull request. If you are a Meta employee, you can view the originating Diff in D110458670.

[cortinico]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

This pull request has been merged in c948b61.