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base repository: react/react
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head repository: react/react
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  • 3 commits
  • 15 files changed
  • 3 contributors

Commits on Sep 3, 2025

  1. [flags] enable opt-in for enableDefaultTransitionIndicator (#34373) 

    So we can test the feature.
    @rickhanlonii
    rickhanlonii authored Sep 3, 2025
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  2. [playground] Upgrade to latest next (#34375) 

    We were still on a canary version of next in the playground, so let's
update to the latest version.
    @poteto
    poteto authored Sep 3, 2025
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  3. Fix: uDV skipped initial value if earlier transition suspended (#34376) 

    Fixes a bug in useDeferredValue's optional `initialValue` argument. In
the regression case, if a new useDeferredValue hook is mounted while an
earlier transition is suspended, the `initialValue` argument of the new
hook was ignored. After the fix, the `initialValue` argument is
correctly rendered during the initial mount, regardless of whether other
transitions were suspended.

The culprit was related to the mechanism we use to track whether a
render is the result of a `useDeferredValue` hook: we assign the
deferred lane a TransitionLane, then entangle that lane with the
DeferredLane bit. During the subsequent render, we check for the
presence of the DeferredLane bit to determine whether to switch to the
final, canonical value.

But because transition lanes can themselves become entangled with other
transitions, the effect is that every entangled transition was being
treated as if it were the result of a `useDeferredValue` hook, causing
us to skip the initial value and go straight to the final one.

The fix I've chosen is to reserve some subset of TransitionLanes to be
used only for deferred work, instead of using entanglement. This is
similar to how retries are already implemented. Originally I tried not
to implement it this way because it means there are now slightly fewer
lanes allocated for regular transitions, but I underestimated how
similar deferred work is to retries; they end up having a lot of the
same requirements. Eventually it may be possible to merge the two
concepts.
    @acdlite
    acdlite authored Sep 3, 2025
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