Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/38990
This PR adds auto-generation of Typescript definitions from Flow source code for packages using the shared monorepo build setup (https://github.com/facebook/react-native/pull/38718).
Today, these are the following Node.js packages:
- `packages/community-cli-plugin`
- `packages/dev-middleware` (⬅️ `emitTypeScriptDefs` enabled)
This also improves emitted Flow definitions (`.js.flow`), by using [`flow-api-translator`](https://www.npmjs.com/package/flow-api-translator) to strip implementations.
**All changes**
- Include `flow-api-translator` and configure this to emit type definitions as part of `yarn build`.
- Add translation from Flow source to TypeScript definitions (`.d.ts`) adjacent to each built file.
- Improve emitted Flow definitions (`.js.flow`), by using `flow-api-translator` to strip implementations (previously, source files were copied). The Flow and TS defs now mirror each other.
- Add `emitFlowDefs` and `emitTypeScriptDefs` options to build config to configure the above.
- Integrate TypeScript compiler to perform program validation on emitted `.d.ts` files.
- This is based on this guide: https://github.com/microsoft/TypeScript-wiki/blob/main/Using-the-Compiler-API.md#a-minimal-compiler.
- Throw an exception on the `rewritePackageExports` step if a package does not define an `"exports"` field.
- Add minimal `flow-typed` definitions for `typescript` 😄.
**Notes on [`flow-api-translator`](https://www.npmjs.com/package/flow-api-translator)**
This project is experimental but is in a more mature state than when we evaluated it earlier in 2023.
- It's now possible to run this tool on our new Node.js packages, since they are exclusively authored using `import`/`export` syntax (a requirement of the tool).
- As a safety net, we run the TypeScript compiler against the generated program, which will fail the build.
Changelog: [Internal]
Reviewed By: robhogan
Differential Revision: D48312463
fbshipit-source-id: 817edb35f911f52fa987946f2d8fc1a319078c9d
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