Fix: Don't read primaryChild.childExpirationTime by acdlite · Pull Request #18457 · react/react (original) (raw)

This is a variant of the fix in 5a0f1d5. We can't rely on the primary fiber's childExpirationTime field to be correct.

In this case, we can read from the Suspense boundary fiber instead. This will include updates that exist in the fallback fiber, but that's not a big deal; the important thing is that we don't drop updates.

Longer term, we'll likely remove fragment reparenting from the Suspense implementation. It's only there to save on memory but because it's the only place we do reparenting, it's been hard to maintain.

If we ever do add reparenting, what this bug demonstrates is that the state tree and the UI tree are not the same thing. It just happens to be that in current React (no reparenting), the "state ancestors" of a node are always subset of its "UI ancestors", which is why we can get away with only having a single return path.