Remove Mutation Check Around commit/measureUpdateViewTransition #32617
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…erMutation pass Also add ContentReset which is also a type of mutation but it's usually accompanied by an Update too.
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rickhanlonii
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There's two ways to find updated View Transitions. One is the "commit/measureNestedViewTransitions" pass which is used to find things in unchanged subtrees. This can only lead to the relayout case since there's can't possibly be any mutations in the subtree. This is only triggered when none of the direct siblings have any mutations at all. The other case is "commit/measureUpdateViewTransition" which is for a ViewTransition that itself has mutations scheduled inside of it which leads to the "update" case. However, there's a case between these two cases. When a direct sibling has a mutation but there's also a ViewTransition exactly at the same level. In that case we can't bail out on the whole set of children so we won't trigger the "nested" case. Previously we also didn't trigger the "commit/measureUpdateViewTransition" case because we first checked if that had any mutations inside of it at all. This leads to neither case picking up this boundary. We could check if the ViewTransition itself has any mutations inside and if not trigger the nested path. There's a simpler way though. Because `commit/measureUpdateViewTransition` is actually just optimistic. The flags are pessimistic and we don't know for sure if there will actually be a mutation until we've traversed the tree. It can sometimes lead to the "relayout" case. So we can just use that same path, knowing that it'll just lead to the layout pass. Therefore it's safe to just remove this check. DiffTrain build for [17d274d](17d274d)
This was referenced Mar 17, 2025
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There's two ways to find updated View Transitions.
One is the "commit/measureNestedViewTransitions" pass which is used to find things in unchanged subtrees. This can only lead to the relayout case since there's can't possibly be any mutations in the subtree. This is only triggered when none of the direct siblings have any mutations at all.
The other case is "commit/measureUpdateViewTransition" which is for a ViewTransition that itself has mutations scheduled inside of it which leads to the "update" case.
However, there's a case between these two cases. When a direct sibling has a mutation but there's also a ViewTransition exactly at the same level. In that case we can't bail out on the whole set of children so we won't trigger the "nested" case. Previously we also didn't trigger the "commit/measureUpdateViewTransition" case because we first checked if that had any mutations inside of it at all. This leads to neither case picking up this boundary.
We could check if the ViewTransition itself has any mutations inside and if not trigger the nested path.
There's a simpler way though. Because
commit/measureUpdateViewTransitionis actually just optimistic. The flags are pessimistic and we don't know for sure if there will actually be a mutation until we've traversed the tree. It can sometimes lead to the "relayout" case. So we can just use that same path, knowing that it'll just lead to the layout pass. Therefore it's safe to just remove this check.