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## Summary
This pull request resolves an issue where consecutive profiling sessions
would cause Dev Tools to freeze due to an infinite loop of state
updates. The problem occurs when the startProfiling function triggers a
call to [`selectCommitIndex(0)` in
SnapshotSelector](https://github.com/facebook/react/blob/89f63f4a7e9976c53915465ab2b84160cab56ea3/packages/react-devtools-shared/src/devtools/views/Profiler/SnapshotSelector.js#L77-L85)
as previous profiling data is available, which causes a re-render. Then,
[ProfilerContextProvider calls
`selectCommitIndex(null)`](https://github.com/facebook/react/blob/89f63f4a7e9976c53915465ab2b84160cab56ea3/packages/react-devtools-shared/src/devtools/views/Profiler/ProfilerContext.js#L231-L241)
to clear the view while profiling is in progress, leading to another
re-render and creating an infinite loop. This behavior was prevented by
clearing the existing profiling data before starting a new session.
Closes#31977Closes#31679
## How did you test this change?
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I ran the Dev Tools locally following [the contributing
guideline](https://github.com/facebook/react/blob/89f63f4a7e9976c53915465ab2b84160cab56ea3/packages/react-devtools/CONTRIBUTING.md).
I observed the freeze at the start of the second profiling session.
Then, I modified the code to clear the store when starting a new session
and ran the Dev Tools again. This time, no freeze was observed.
Before:
https://github.com/user-attachments/assets/9d790f84-f6d0-4951-8202-e599cf8d225b
After:
https://github.com/user-attachments/assets/af097019-0b8f-49dd-8afc-0f6cd72af787
Stacked on https://github.com/facebook/react/pull/31132. See last
commit.
There are 2 issues:
1. We've been recording timeline events, even if Timeline Profiler was
not supported by the Host. We've been doing this for React Native, for
example, which would significantly regress perf of recording a profiling
session, but we were not even using this data.
2. Currently, we are generating component stack for every state update
event. This is extremely expensive, and we should not be doing this.
We can't currently fix the second one, because we would still need to
generate all these stacks, and this would still take quite a lot of
time. As of right now, we can't generate a component stack lazily
without relying on the fact that reference to the Fiber is not stale.
With `enableOwnerStacks` we could populate component stacks in some
collection, which would be cached at the Backend, and then returned only
once Frontend asks for it. This approach also eliminates the need for
keeping a reference to a Fiber.
We can't wait for a response from Backend, because it might take some
time to actually finish profiling.
We should keep a flag on the frontend side, so user can quickly see the
feedback in the UI.
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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.
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10. If you haven't already, complete the CLA.
Learn more about contributing:
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-->
## Summary
Profiling fails sometimes because `onProfilingStatus` is called
repeatedly on some occasions, e.g. multiple calls to
`getProfilingStatus`.
Subsequent calls should be a no-op if the profiling status hasn't
changed.
Reported via #30661#28838.
> [!TIP]
> Hide whitespace changes on this PR
<img width="328" alt="screenshot showing the UI controls for hiding
whitespace changes on GitHub"
src="https://github.com/user-attachments/assets/036385cf-2610-4e69-a717-17c05d7ef047">
## How did you test this change?
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their output, screenshots / videos if the pull request changes the user
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How exactly did you verify that your PR solves the issue you wanted to
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Tested as part of Fusebox implementation of reload-to-profile.
https://github.com/facebook/react/pull/31021?#discussion_r1770589753
The old version of prettier we were using didn't support the Flow syntax
to access properties in a type using `SomeType['prop']`. This updates
`prettier` and `rollup-plugin-prettier` to the latest versions.
I added the prettier config `arrowParens: "avoid"` to reduce the diff
size as the default has changed in Prettier 2.0. The largest amount of
changes comes from function expressions now having a space. This doesn't
have an option to preserve the old behavior, so we have to update this.
* Facebook -> Meta in copyright
rg --files | xargs sed -i 's#Copyright (c) Facebook, Inc. and its affiliates.#Copyright (c) Meta Platforms, Inc. and affiliates.#g'
* Manual tweaks
* Enable prefer-const rule
Stylistically I don't like this but Closure Compiler takes advantage of
this information.
* Auto-fix lints
* Manually fix the remaining callsites
DevTools previously used the NPM events package for dispatching events. This package has an unfortunate flaw though- if a listener throws during event dispatch, no subsequent listeners are called. I've replaced that event dispatcher with my own implementation that ensures all listeners are called before it re-throws an error.
This commit replaces that event emitter with a custom implementation that calls all listeners before re-throwing an error.
