If React finishes rendering a tree, delays committing it (e.g.
Suspense), then subsequently starts over or renders a new tree, the
pending tree is no longer valid. That's because rendering a new work-in
progress mutates the old one in place.
The current structure of the work loop makes this hard to reason about
because, although `renderRoot` and `commitRoot` are separate functions,
they can't be interleaved. If they are interleaved by accident, it
either results in inconsistent render output or invariant violations
that are hard to debug.
This commit adds an invariant that throws if the new tree is the same as
the old one. This won't prevent all bugs of this class, but it should
catch the most common kind.
To implement the invariant, I store the finished tree on a field on the
root. We already had a field for this, but it was only being used for
the unstable `createBatch` feature.
A more rigorous way to address this type of problem could be to unify
`renderRoot` and `commitRoot` into a single function, so that it's
harder to accidentally interleave the two phases. I plan to do something
like this in a follow-up.
* Add ReactDOM.unstable_createSyncRoot
- `ReactDOM.unstable_createRoot` creates a Concurrent Mode root.
- `ReactDOM.unstable_createSyncRoot` creates a Batched Mode root. It
does not support `createBatch`.
- `ReactDOM.render` creates a Legacy Mode root. It will eventually be
deprecated and possibly moved to a separate entry point, like
`react-dom/legacy`.
* Rename internal ReactRoot types
* Add Batched Mode
React has an unfortunate quirk where updates are sometimes synchronous
-- where React starts rendering immediately within the call stack of
`setState` — and sometimes batched, where updates are flushed at the
end of the current event. Any update that originates within the call
stack of the React event system is batched. This encompasses most
updates, since most updates originate from an event handler like
`onClick` or `onChange`. It also includes updates triggered by lifecycle
methods or effects. But there are also updates that originate outside
React's event system, like timer events, network events, and microtasks
(promise resolution handlers). These are not batched, which results in
both worse performance (multiple render passes instead of single one)
and confusing semantics.
Ideally all updates would be batched by default. Unfortunately, it's
easy for components to accidentally rely on this behavior, so changing
it could break existing apps in subtle ways.
One way to move to a batched-by-default model is to opt into Concurrent
Mode (still experimental). But Concurrent Mode introduces additional
semantic changes that apps may not be ready to adopt.
This commit introduces an additional mode called Batched Mode. Batched
Mode enables a batched-by-default model that defers all updates to the
next React event. Once it begins rendering, React will not yield to
the browser until the entire render is finished.
Batched Mode is superset of Strict Mode. It fires all the same warnings.
It also drops the forked Suspense behavior used by Legacy Mode, in favor
of the proper semantics used by Concurrent Mode.
I have not added any public APIs that expose the new mode yet. I'll do
that in subsequent commits.
* Suspense in Batched Mode
Should have same semantics as Concurrent Mode.
* Use RootTag field to configure type of root
There are three types of roots: Legacy, Batched, and Concurrent.
* flushSync should not flush batched work
Treat Sync and Batched expiration times separately. Only Sync updates
are pushed to our internal queue of synchronous callbacks.
Renamed `flushImmediateQueue` to `flushSyncCallbackQueue` for clarity.
* Don't consider "Never" expiration as part of most recent event time
This doesn't happen with deprioritization since those are not "updates"
by themselves so they don't go into this accounting.
However, they are real updates if they were scheduled as Idle pri using
the scheduler explicitly. It's unclear what suspense should do for these
updates. For offscreen work, we probably want them to commit immediately.
No point in delay them since they're offscreen anyway. However if this is
an explicit but very low priority update that might not make sense.
So maybe this means that these should have different expiration times?
In this PR I just set the suspense to the lowest JND.
However, we don't want is for these things to commit earlier in case
they got batched in with other work so I also ensured that they're not
accounted for in in the workInProgressRootMostRecentEventTime calculation
at all. This makes them commit immediately if they're by themselves, or
after the JND of whatever they were batched in with.
Ultimately, I think that we should probably never schedule anything at
Never that isn't truly offscreen so this should never happen.
However, that begs the question what happens with very low pri work that
suspends. Do we always work at that level first?
* Adjust test to account for the new shorter suspense time
* Warn when suspending at wrong priority
Adds a warning when a user-blocking update is suspended.
Ideally, all we would need to do is check the current priority level.
But we currently have no rigorous way to distinguish work that was
scheduled at user- blocking priority from work that expired a bit and
was "upgraded" to a higher priority. That's because we don't schedule
separate callbacks for every level, only the highest priority level per
root. The priority of subsequent levels is inferred from the expiration
time, but this is an imprecise heuristic.
However, we do store the last discrete pending update per root. So we
can reliably compare to that one. (If we broaden this warning to include
high pri updates that aren't discrete, then this won't be sufficient.)
My rationale is that it's better for this warning to have false
negatives than false positives.
Potential follow-ups:
- Bikeshed more on the message. I don't like what I landed on that much
but I think it's good enough to start.
- Include the names of the components that updated. (The ideal place to
fire the warning is during the setState call but we don't know if
something will suspend until the next update. Maybe we could be clever
and warn during a subsequent update to the same component?)
* Move Suspense priority check to throwException
* Fixes a bug in the cancellation logic. The cancel events are now correctly listened to on the root.
* Fixes cancellation in Safari by using the dragstart event as a proxy for cancellation (i.e., the event dispatched when move-during-press occurs on an anchor tag)
* [React Native] Inline calls to FabricUIManager in shared code
* Call global.nativeFabricUIManager directly as short term fix
* Add flow types
* Add nativeFabricUIManager global to eslint config
* Adding eslint global to bundle validation script
Called when focus visibility changes. Focus is only considered visible if a
focus event occurs after keyboard navigation. This provides a way for people to
provide visual focus styles for keyboard accessible UIs without those styles
appearing if focus is triggered by mouse, touch, pen.
This patch fixes an issue related to determining whether the end event occurs
within the responder region. Previously we only checked if the event target was
within the responder region for moves, otherwise we checked if the target was
within the event component. Since the dimensions of the child element can
change after activation, we need to recalculate the responder region before
deactivation as well if the target is not within the event component.
