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Alex Hunt 0b9969f7f5 Prune no-op Omit keys from generated types (#56824) 
Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56824

Update the `simplifyTypes` transform (Flow → TS generation) to prune non-overlapping keys from `Omit<>` helpers in TypeScript `interface` unions.

This greatly reduces API snapshot churn/inflation in the next two diffs, which convert a number of `type` declarations (trivial unions) to `interface` (`Omit<>` required for correct union).

#### In detail

`flow-api-translator` emits `Omit<ParentType, keys>` to faithfully translate Flow's object spread override semantics to TypeScript.

```
// Flow
type Base = {x: string, y: number};
type Child = {...Base, x: boolean}; // Later properties in an object spread override earlier ones

// TypeScript
type Base = {x: string; y: number};
type Child = Omit<Base, "x" | "y"> & {x: boolean};  // Later properties in an object spread *merge*, rather than override. So we must use Omit<> for matched keys.
```

For `interface` type unions with overlapping keys, this can result in a number of unnecessary lines in the API snapshot, with little/no human readable value.

This diff extends existing `Omit<>` handling by `simplifyTypes` to recursively resolve all property keys reachable from a type, and prune keys that don't exist on the parent type.

```
// TypeScript
type Child = Omit<Base, "x"> & {x: boolean};  // Only "x" matched - strip `| "y"`
type ChildTwo = Base & {z: string};  // No property collision - strip entire `Omit<>`
```

- See changes to `ReactNativeApi.d.ts`, [P2325468482](https://www.internalfb.com/phabricator/paste/view/P2325468482?view=diff) for examples.
- **Decision point**: This diff opts to preserve correctness in TS — even though the snapshot isn't/isn't intended to be read directly/programatically, vs the conciseness tradeoff if we dropped all `Omit<>`s (human readable but ambiguous to the typechecker).

Changelog: [Internal] - JS API snapshot changes are a simplification refactor only

Reviewed By: robhogan

Differential Revision: D105150070

fbshipit-source-id: 43b0ef517164332a5cfaee7a5de5747749ac5e7c
2026-05-14 04:16:19 -07:00
..
build-types
Prune no-op Omit keys from generated types (#56824)
2026-05-14 04:16:19 -07:00
diff-api-snapshot
Transform $Values to Values (#55136)
2026-01-13 13:47:19 -08:00
config.js
Consolidate JS API scripts under scripts/js-api/, update docs (#52469)
2025-07-07 15:04:37 -07:00
README.md
Fix incorrect package name and filename in scripts/js-api/README.md (#56362)
2026-04-15 04:29:37 -07:00

README.md

scripts/js-api

TypeScript build pipeline for React Native's JavaScript API.

Overview

yarn build-types is a custom build pipeline for translating React Native's Flow source code to TypeScript.

Specifically, it reduces the runtime JavaScript API of react-native into two outputs:

  • Generated TypeScript types
    Public user types for react-native, shipped to npm
    packages/react-native/types_generated/
  • ‌Public API snapshot
    Snapshot file of the public API shape, used by maintainers
    packages/react-native/ReactNativeApi.d.ts

Dependencies

yarn build-types makes use of the following dependencies, composed with other pre/post transformation steps and dependency resolution.

Usage

Build generated types + API snapshot

Maintainers should run this script whenever making intentional API changes.

# Build types + API snapshot
yarn build-types [--validate]

# Build types without API snapshot
yarn build-types --skip-snapshot

Diff API snapshot compatibility

This script is run by CI to compare changes to ReactNativeApi.d.ts between commits.

# Compare two versions of the API snapshot
yarn js-api-diff <before.d.ts> <after.d.ts>

{
  "result": "BREAKING",
  "changedApis": [
    "ViewStyle"
  ]
}

Configuration

Sparse configuration options are defined and documented in scripts/js-api/config.js.

About the two output formats

Generated TypeScript types

types_generated/

Directory providing TypeScript user types for the react-native package, distributed via npm.

  • Gitignored.
  • Scoped to the index.d.ts entry point via package.json#exports.
  • Preserves unstable_ and experimental_ APIs.
  • Preserves doc comments.
  • Preserves source file names (for go to definition).

Public API snapshot

ReactNativeApi.d.ts

Provides a human-readable, maintainable reference of the React Native's public JavaScript API, optimized for developers and diff tooling.

  • Committed to the repo.
  • Strips unstable_ and experimental_ APIs.
  • Strips doc comments.
  • Strips source file names (types are merged into a single program).
  • Versions exported APIs with an 8 char SHA hash, which will be updated when any input type dependencies change shape.
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