[pull] main from facebook:main #253
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## Summary Part 1 of adding a "Config Override" panel to the React compiler playground. The panel is placed to the left of the current input section, and supports converting the comment pragmas in the input section to a JavaScript-based config. Backwards sync has not been implemented yet. NOTE: I have added support for a new `OVERRIDE` type pragma to add support for Map and Function types. (For now, the old pragma format is still intact) ## Testing Example of the config overrides synced to the source code: <img width="1542" height="527" alt="Screenshot 2025-08-28 at 3 38 13 PM" src="https://github.com/user-attachments/assets/d46e7660-61b9-4145-93b5-a4005d30064a" />
Small PR to update our readme for eslint-plugin-react-hooks, to better describe what a minimal but complete eslint config would look like.
## Summary Update the CodeSandbox CI configuration to use Node 20 instead of Node 18, so that it matches the Node version specified in .nvmrc. This ensures consistency between local development environments and CI builds, reducing the risk of version-related build issues. Closes #34328 ## How did you test this change? - Verified that .nvmrc specifies Node 20 and .codesandbox/ci.json is updated accordingly. - Locally switched to Node 20 using nvm use 20 and successfully ran build scripts for all packages: `react`, `react-dom`, `react-server-dom-webpack`, and `scheduler`. - Confirmed there are no Node 20–specific build errors or warnings locally. - CI on the feature branch will now run with Node 20, and all builds are expected to succeed.
A few libraries are known to be incompatible with memoization, whether manually via `useMemo()` or via React Compiler. This puts us in a tricky situation. On the one hand, we understand that these libraries were developed prior to our documenting the [Rules of React](https://react.dev/reference/rules), and their designs were the result of trying to deliver a great experience for their users and balance multiple priorities around DX, performance, etc. At the same time, using these libraries with memoization — and in particular with automatic memoization via React Compiler — can break apps by causing the components using these APIs not to update. Concretely, the APIs have in common that they return a function which returns different values over time, but where the function itself does not change. Memoizing the result on the identity of the function will mean that the value never changes. Developers reasonable interpret this as "React Compiler broke my code". Of course, the best solution is to work with developers of these libraries to address the root cause, and we're doing that. We've previously discussed this situation with both of the respective libraries: * React Hook Form: react-hook-form/react-hook-form#11910 (comment) * TanStack Table: #33057 (comment) and TanStack/table#5567 In the meantime we need to make sure that React Compiler can work out of the box as much as possible. This means teaching it about popular libraries that cannot be memoized. We also can't silently skip compilation, as this confuses users, so we need these error messages to be visible to users. To that end, this PR adds: * A flag to mark functions/hooks as incompatible * Validation against use of such functions * A default type provider to provide declarations for two known-incompatible libraries Note that Mobx is also incompatible, but the `observable()` function is called outside of the component itself, so the compiler cannot currently detect it. We may add validation for such APIs in the future. Again, we really empathize with the developers of these libraries. We've tried to word the error message non-judgementally, because we get that it's hard! We're open to feedback about the error message, please let us know.
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