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[web][ck] Don't remove (then add) embedded views. #32948
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When computing the diff of embedded views between a frame and the next (diffViewList), remove all views from viewsToRemove that are also in viewsToAdd. The framework needs a frame to re-render a view after it's been removed, and the browser is able to understand that we want to "move" a view, just by adding it elsewhere. Added some extra unit tests for the new behavior.
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Not entirely sure how to trigger/test this case, but looking at how the code accesses the viewClipChain, this branch of the code seems also vulnerable to the same error :/
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When computing the diff of embedded views between a frame and the next (
diffViewList), prevent viewIds from being returned both in theviewsToRemoveandviewsToAddof the diff (prefer them onviewsToAdd).If we let the diff remove views that are going to be added immediately afterwards, they get disposed of and then they cause a null access error when the engine attempts to add them a few lines below (the framework would need an extra frame to re-inject the missing view after it's been removed).
The browser is able to understand that we want to "move" an html element just by adding it elsewhere; so the solution is to ensure that
viewsToRemoveandviewsToAdddo not share view ids. (or: remove all viewIds fromviewsToRemovethat are going to be added byviewsToAdd).Tests
Issue
CanvaskitthrowsThe following TypeErrorImpl was thrown during a scheduler callback: Unexpected null value.flutter#94945Pre-launch Checklist
writing and running engine tests.
///).If you need help, consider asking for advice on the #hackers-new channel on Discord.