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State update bug in concurrent mode #14698

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merged 2 commits into from
Jan 25, 2019
Merged

State update bug in concurrent mode #14698

merged 2 commits into from
Jan 25, 2019

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bvaughn
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@bvaughn bvaughn commented Jan 24, 2019 •
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I think this PR captures a bug that was reported internally at Facebook. I believe this code should work for both sync and concurrent mode, but the update fails for concurrent mode.

acdlite
acdlite approved these changes Jan 24, 2019
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packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -1252,7 +1252,7 @@ function mountIndeterminateComponent(
) {
// Only double-render components with Hooks
if (workInProgress.memoizedState !== null) {
renderWithHooks(
value = renderWithHooks(
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@acdlite acdlite Jan 24, 2019 •
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Do the same for the other occurrences of renderWithHooks

@bvaughn bvaughn force-pushed the concurrent-mode-state-update-bug branch from c2a69ce to 6ac4104 Compare January 24, 2019 23:58
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acdlite commented Jan 25, 2019 •
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Explanation of why this fix works, for others who are interested:

When you call renderWithHooks during the initial render, React creates state queues for each of the State/Reducer Hooks. Those queues are bound to the dispatch method that is returned by the Hook, which is then closed over by event handlers, which in turn are included as part of the final children result that is returned by the component. These queues are also coupled to the internal list of Hook nodes that is stored on fiber.memoizedState.

The cause of bug was that, in dev, we were calling renderWithHooks a second time, but we weren't using the children that correspond to that call.

@acdlite acdlite merged commit f11a9c1 into facebook:master Jan 25, 2019
@bvaughn bvaughn deleted the concurrent-mode-state-update-bug branch January 25, 2019 00:38
n8schloss pushed a commit to n8schloss/react that referenced this pull request Jan 31, 2019
@bvaughn @n8schloss
State update bug in concurrent mode (facebook#14698)
9e216fc 
* State update bug in concurrent mode

* Fix bug introduced by double-rendering Functions using hooks
@acdlite acdlite mentioned this pull request Apr 8, 2020
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@bvaughn @acdlite @facebook-github-bot