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ff1664b11b
fixes NEXT-164 ## Context This PR fixes an issue happening when using `next/image` or `next/link` where rendering them caused sync re-renders with React. This breaks [selective hydration](https://github.com/reactwg/react-18/discussions/130) in React. ## The fix The cause of this behaviour is that we're calling `setState` in a ref mount, which basically "forces" React to disable concurrent rendering. It finishes the render, runs synchronously the passive effects and re-renders again to make sure that everything is in sync, all of that in without yielding to the browser to paint. Here in this case, the `setState` call is because of the `useIntersectionObserver` hook. It's implemented in a way that requires the user to call a setter that will store the ref value in a component state variable to re-trigger a render and re-run the effect to create the intersection observer. This is not necessary as the ref init phase always runs before the passive effect runs, so we can just copy the ref to another ref inside `useIntersectionObserver` without triggering a re-render. ## Before/After 1st screenshot: before 2nd screenshot: after Basically on the first screenshot, you can see that React is doing a synchronous re-render (see `flushPassiveEffects`). This is not good. If you look at screenshot 2, you can see it does not happen anymore and that the passive effects are flushed in another block in the flamegraph. <img width="1110" alt="CleanShot 2023-01-23 at 14 30 11@2x" src="https://user-images.githubusercontent.com/11064311/214051860-c42d2849-cd10-4922-a3e0-9b715fc87b23.png"> <img width="520" alt="CleanShot 2023-01-23 at 14 29 01@2x" src="https://user-images.githubusercontent.com/11064311/214051555-04adf516-9c0b-4056-ac65-1ef33614c767.png"> ## Bug - [ ] Related issues linked using `fixes #number` - [ ] Integration tests added - [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md) ## Feature - [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR. - [ ] Related issues linked using `fixes #number` - [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added - [ ] Documentation added - [ ] Telemetry added. In case of a feature if it's used or not. - [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md) ## Documentation / Examples - [ ] Make sure the linting passes by running `pnpm build && pnpm lint` - [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md) |
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| UPGRADING.md | ||
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Next.js
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Visit https://nextjs.org/learn to get started with Next.js.
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Contributing
Please see our contributing.md.
Good First Issues
We have a list of good first issues that contain bugs that have a relatively limited scope. This is a great place to get started, gain experience, and get familiar with our contribution process.
Authors
- Tim Neutkens (@timneutkens)
- Naoyuki Kanezawa (@nkzawa)
- Guillermo Rauch (@rauchg)
- Arunoda Susiripala (@arunoda)
- Tony Kovanen (@tonykovanen)
- Dan Zajdband (@impronunciable)
Security
If you believe you have found a security vulnerability in Next.js, we encourage you to responsibly disclose this and not open a public issue. We will investigate all legitimate reports. Email security@vercel.com to disclose any security vulnerabilities.