[DevTools] Keep a Suspense Tree Parellel to the Instance tree in the Backend #34050
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…w set Avoids thrashing the parent set when we're really just readding the same thing.
If you're awaiting the same resource in multiple places we only need to show it once per Suspense boundary and if another parent boundary already awaits it but using a different await then it should dedupe in the child.
There are many suspense boundaries that never have anything that suspend them or even if they do, the same data is also suspending a parent anyway so in effect they never can contribute to the loading sequence. This tracks the first time we add a unique io to a boundary or the first time a parent removes an io which then makes a child the unique suspender. We never return to set this to false if it ever had unique suspenders even if it doesn't now.
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Follow up to #34050. It's not actually possible to suspend *above* the root since even if you suspend in the first child position, you're still suspending the HostRoot which always has a corresponding FiberInstance and SuspenseNode.
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This keeps a data structure of Suspense boundaries and the root which can keep track which boundaries might participate in a loading sequence and everything that suspends them. This will power the Suspense tab.
Now when you select a
<Suspense>boundary the "suspended by" section shows the whole boundary instead of just that component.In the future, we'll likely need to add "Activity" boundaries to this tree as well, so that we can track what suspended the root of an Activity when filtering a subtree. Similar to how the root SuspenseNode now tracks suspending at the root. Maybe it's ok to just traverse to collect this information on-demand when you select one though since this doesn't contribute to the deduping.
We'll also need to add implicit Suspense boundaries for the rows of a SuspenseList with
tail=hidden/collapsed.