This was really meant to be there from the beginning. A `cache()`:ed
entry has a life time. On the server this ends when the render finishes.
On the client this ends when the cache of that scope gets refreshed.
When a cache is no longer needed, it should be possible to abort any
outstanding network requests or other resources. That's what
`cacheSignal()` gives you. It returns an `AbortSignal` which aborts when
the cache lifetime is done based on the same execution scope as a
`cache()`ed function - i.e. `AsyncLocalStorage` on the server or the
render scope on the client.
```js
import {cacheSignal} from 'react';
async function Component() {
await fetch(url, { signal: cacheSignal() });
}
```
For `fetch` in particular, a patch should really just do this
automatically for you. But it's useful for other resources like database
connections.
Another reason it's useful to have a `cacheSignal()` is to ignore any
errors that might have triggered from the act of being aborted. This is
just a general useful JavaScript pattern if you have access to a signal:
```js
async function getData(id, signal) {
try {
await queryDatabase(id, { signal });
} catch (x) {
if (!signal.aborted) {
logError(x); // only log if it's a real error and not due to cancellation
}
return null;
}
}
```
This just gets you a convenient way to get to it without drilling
through so a more idiomatic code in React might look something like.
```js
import {cacheSignal} from "react";
async function getData(id) {
try {
await queryDatabase(id);
} catch (x) {
if (!cacheSignal()?.aborted) {
logError(x);
}
return null;
}
}
```
If it's called outside of a React render, we normally treat any cached
functions as uncached. They're not an error call. They can still load
data. It's just not cached. This is not like an aborted signal because
then you couldn't issue any requests. It's also not like an infinite
abort signal because it's not actually cached forever. Therefore,
`cacheSignal()` returns `null` when called outside of a React render
scope.
Notably the `signal` option passed to `renderToReadableStream` in both
SSR (Fizz) and RSC (Flight Server) is not the same instance that comes
out of `cacheSignal()`. If you abort the `signal` passed in, then the
`cacheSignal()` is also aborted with the same reason. However, the
`cacheSignal()` can also get aborted if the render completes
successfully or fatally errors during render - allowing any outstanding
work that wasn't used to clean up. In the future we might also expand on
this to give different
[`TaskSignal`](https://developer.mozilla.org/en-US/docs/Web/API/TaskSignal)
to different scopes to pass different render or network priorities.
On the client version of `"react"` this exposes a noop (both for
Fiber/Fizz) due to `disableClientCache` flag but it's exposed so that
you can write shared code.
This PR introduces a new experimental hook `useResourceEffect`, which is
something that we're doing some very early initial tests on.
This may likely not pan out and will be removed or modified if so.
Please do not rely on it as it will break.
<!--
Thanks for submitting a pull request!
We appreciate you spending the time to work on these changes. Please
provide enough information so that others can review your pull request.
The three fields below are mandatory.
Before submitting a pull request, please make sure the following is
done:
1. Fork [the repository](https://github.com/facebook/react) and create
your branch from `main`.
2. Run `yarn` in the repository root.
3. If you've fixed a bug or added code that should be tested, add tests!
4. Ensure the test suite passes (`yarn test`). Tip: `yarn test --watch
TestName` is helpful in development.
5. Run `yarn test --prod` to test in the production environment. It
supports the same options as `yarn test`.
6. If you need a debugger, run `yarn test --debug --watch TestName`,
open `chrome://inspect`, and press "Inspect".
7. Format your code with
[prettier](https://github.com/prettier/prettier) (`yarn prettier`).
8. Make sure your code lints (`yarn lint`). Tip: `yarn linc` to only
check changed files.
9. Run the [Flow](https://flowtype.org/) type checks (`yarn flow`).
10. If you haven't already, complete the CLA.
Learn more about contributing:
https://reactjs.org/docs/how-to-contribute.html
-->
## Summary
In order to adopt react 19's ref-as-prop model, Flow needs to eliminate
all the places where they are treated differently.
`React.AbstractComponent` is the worst example of this, and we need to
eliminate it.
This PR eliminates them from the react repo, and only keeps the one that
has 1 argument of props.
## How did you test this change?
yarn flow
In order to support using the compiler on versions of React prior to 19,
we need the ability to statically import `c` (aka useMemoCache) or
fallback to a polyfill supplied by `react-compiler-runtime` (note: this
is a separate npm package, not to be confused with
`react/compiler-runtime`, which is currently a part of react).
To do this we first need to re-export `useMemoCache` under the top level
React namespace again, which is additive and thus non-breaking. Doing so
allows `react-compiler-runtime` to statically either re-export
`React.__COMPILER_RUNTIME.c` or supply a polyfill, without the need for
a dynamic import which is finicky to support due to returning a promise.
In later PRs I will remove `react/compiler-runtime` and update the
compiler to emit imports to `react-compiler-runtime` instead.
Only with the enableOwnerStacks flag (which is not on in www).
This is a new DEV-only API to be able to implement what we do for
console.error in user space.
This API does not actually include the current stack that you'd get from
`new Error().stack`. That you'd have to add yourself.
This adds the ability to have conditional development exports because we
plan on eventually having separate ESM builds that use the "development"
or "production" export conditions.
NOTE: This removes the export of `act` from `react` in prod (as opposed
to a function that throws) - inline with what we do with other
conditional exports.
Sebastian Markbåge
lauren
Ricky
Sam Zhou