Certain fiber types may have a ref attached to them. The main ones are
HostComponent and ClassComponent. During the render phase, we check if a
ref was passed to it, and if so, we schedule a Ref effect: `markRef`.
Currently, we're not consistent about whether we call `markRef` in the
begin phase or the complete phase. For some fiber types, I found that
`markRef` was called in both phases, causing redundant work.
After some investigation, I don't believe it's necessary to call
`markRef` in both the begin phase and the complete phase, as long as you
don't bail out before calling `markRef`.
I though that maybe it had to do with the
`attemptEarlyBailoutIfNoScheduledUpdates` branch, which is a fast path
that skips the regular begin phase if no new props, state, or context
were passed. But if the props haven't changed (referentially — the
`memo` and `shouldComponentUpdate` checks happen later), then it follows
that the ref couldn't have changed either. This is true even in the old
`createElement` runtime where `ref` is stored on the element instead of
as a prop, because there's no way to pass a new ref to an element
without also passing new props. You might argue this is a leaky
assumption, but since we're shifting ref to be just a regular prop
anyway, I think it's the correct way to think about it going forward.
I think the pattern of calling `markRef` in the complete phase may have
been left over from an earlier iteration of the implementation before
the bailout logic was structured like it is today.
So, I removed all the `markRef` calls from the complete phase. In the
case of ScopeComponent, which had no corresponding call in the begin
phase, I added one.
We already had a test that asserted that a ref is reattached even if the
component bails out, but I added some new ones to be extra safe.
The reason I'm changing this this is because I'm working on a different
change to move the ref handling logic in `coerceRef` to happen in render
phase of the component that accepts the ref, instead of during the
parent's reconciliation.
DiffTrain build for [c820097716](https://github.com/facebook/react/commit/c820097716c3d9765bf85bf58202a4975d99e450)
This won't ever be serialized and is likely just a mistake.
This should be covered by the "use server" compiler since it ensures
that something that accepts a "this" won't be allowed to compile and if
it doesn't accept it, TypeScript should ideally forbid it to be passed.
So maybe this is unnecessary.
DiffTrain build for [65a0e2b25e](https://github.com/facebook/react/commit/65a0e2b25ec4642f83c32d7599b5252c3955a60b)
It's possible for the same function instance to appear more than once in
the same graph or even the same file.
Currently this errors on trying to reconfigure the property but it
really doesn't matter which one wins. First or last.
Regardless there will be an entry point generated that can get them.
DiffTrain build for [9444c51c7e](https://github.com/facebook/react/commit/9444c51c7e44936c24e1f44db905cfd45c51cff3)
Also warn for symbols.
It's weird because for objects we throw a hard error but functions we do
a dev only check. Mainly because we have an object branch anyway.
In the object branch we have some built-ins that have bad errors like
forwardRef and memo but since they're going to become functions later, I
didn't bother updating those. Once they're functions those names will be
part of this.
DiffTrain build for [c1fd2a91b1](https://github.com/facebook/react/commit/c1fd2a91b1042c137d750be85e5998f699a54d2a)
ErrorBoundaries are currently not fully composable. The reason is if you
decide your boundary cannot handle a particular error and rethrow it to
higher boundary the React runtime does not understand that this throw is
a forward and it recreates the component stack from the Boundary
position. This loses fidelity and is especially bad if the boundary is
limited it what it handles and high up in the component tree.
This implementation uses a WeakMap to store component stacks for values
that are objects. If an error is rethrown from an ErrorBoundary the
stack will be pulled from the map if it exists. This doesn't work for
thrown primitives but this is uncommon and stashing the stack on the
primitive also wouldn't work
DiffTrain build for [a9cc32511a](https://github.com/facebook/react/commit/a9cc32511a12c261ee719e5383818182800d6af4)
Same as #28327 but for Fizz.
One thing that's weird about this recoverable error is that we don't
send the regular stack for it, just the component stack it seems. This
is missing some potential information and if we move toward integrated
since stacks it would be one thing.
DiffTrain build for [2e470a788e](https://github.com/facebook/react/commit/2e470a788e359e34feeadb422daaff046baf66cc)
Also deals with symbols. Alternative to #28312.
We currently always normalize rejections or thrown values into `Error`
objects. Partly because in prod it'll be an error object and you
shouldn't fork behavior on knowing the value outside a digest. We might
want to even make the message always opaque to avoid being tempted and
then discover in prod that it doesn't work.
However, we do include the message in DEV.
If this is a non-Error object we don't know what the properties mean.
Ofc, we don't want to include too much information in the rendered
string, so we use the general `describeObjectForErrorMessage` helper.
Unfortunately it's pretty conservative about emitting values so it's
likely to exclude any embedded string atm. Could potentially expand it a
bit.
We could in theory try to serialize as much as possible and re-throw the
actual object to allow for inspection to be expanded inside devtools
which is what I plan on for consoles, but since we're normalizing to an
Error this is in conflict with that approach.
DiffTrain build for [a7144f297c](https://github.com/facebook/react/commit/a7144f297c1c6fe457ca30ce6a211ab59feac11e)
Previously, `<Context>` was equivalent to `<Context.Consumer>`. However,
since the introduction of Hooks, the `<Context.Consumer>` API is rarely
used. The goal here is to make the common case cleaner:
```js
const ThemeContext = createContext('light')
function App() {
return (
<ThemeContext value="dark">
...
</ThemeContext>
)
}
function Button() {
const theme = use(ThemeContext)
// ...
}
```
This is technically a breaking change, but we've been warning about
rendering `<Context>` directly for several years by now, so it's
unlikely much code in the wild depends on the old behavior. [Proof that
it warns today (check
console).](https://codesandbox.io/p/sandbox/peaceful-nobel-pdxtfl)
---
**The relevant commit is 5696782b428a5ace96e66c1857e13249b6c07958.** It
switches `createContext` implementation so that `Context.Provider ===
Context`.
The main assumption that changed is that a Provider's fiber type is now
the context itself (rather than an intermediate object). Whereas a
Consumer's fiber type is now always an intermediate object (rather than
it being sometimes the context itself and sometimes an intermediate
object).
My methodology was to start with the relevant symbols, work tags, and
types, and work my way backwards to all usages.
This might break tooling that depends on inspecting React's internal
fields. I've added DevTools support in the second commit. This didn't
need explicit versioning—the structure tells us enough.
DiffTrain build for [14fd9630ee](https://github.com/facebook/react/commit/14fd9630ee04387f4361da289393234e2b7d93b6)
There are three parts to an RSC set up:
- React
- Bundler
- Endpoints
Most customizability is in the bundler configs. We deal with those as
custom builds.
To create a full set up, you need to also configure ways to expose end
points for example to call a Server Action. That's typically not
something the bundler is responsible for even though it's responsible
for gathering the end points that needs generation. Exposing which
endpoints to generate is a responsibility for the bundler.
Typically a meta-framework is responsible for generating the end points.
There's two ways to "call" a Server Action. Through JS and through a
Form. Through JS we expose the `callServer` callback so that the
framework can call the end point.
Forms by default POST back to the current page with an action serialized
into form data, which we have a decoder helper for. However, this is not
something that React is really opinionated about just like we're not
opinionated about the protocol used by callServer.
This exposes an option to configure the encoding of the form props.
`encodeFormAction` is to the SSR is what `callServer` is to the Browser.
DiffTrain build for [8d48183291](https://github.com/facebook/react/commit/8d48183291870898ec42ac1f84482d9d26789424)
That way we can use it for debug information like component stacks and
DevTools. I used an extra stack argument in Child Fiber to track this as
it's flowing down since it's not just elements where we have this info
readily available but parent arrays and lazy can merge this into the
Fiber too. It's not great that this is a dev-only argument and I could
track it globally but seems more likely to make mistakes.
It is possible for the same debug info to appear for multiple child
fibers like when it's attached to a fragment or a lazy that resolves to
a fragment at the root. The object identity could be used in these
scenarios to infer if that's really one server component that's a parent
of all children or if each child has a server component with the same
name.
This is effectively a public API because you can use it to stash
information on Promises from a third-party service - not just Server
Components. I started outline the types for this for some things I was
planning to add but it's not final.
I was also planning on storing it from `use(thenable)` for when you
suspend on a Promise. However, I realized that there's no Hook instance
for those to stash it on. So it might need a separate data structure to
stash the previous pass over of `use()` that resets each render.
No tests yet since I didn't want to test internals but it'll be covered
once we have debugging features like component stacks.
DiffTrain build for [3f93ca1c8d](https://github.com/facebook/react/commit/3f93ca1c8dec1fd85df4dbb748a2df9438fc699f)
This pains me because `React.Children` is really already
pseudo-deprecated.
`React.Children` takes any children that `React.Node` takes. We now
support Lazy and Thenable in this position elsewhere, but it errors in
`React.Children`.
This becomes an issue with async Server Components which can resolve
into a Lazy and in the future Lazy will just become Thenables. Which
causes this to error.
There are a few different semantics we could have:
1) Error like we already do (#28280). `React.Children` is about
introspecting children. It was always sketchy because you can't
introspect inside an abstraction anyway. With Server Components we fold
away the components so you can actually introspect inside of them kind
of but what they do is an implementation detail and you should be able
to turn it into a Client Component at any point. The type of an Element
passing the boundary actually reduces to `React.Node`.
2) Suspend and unwrap the Node (this PR). If we assume that Children is
called inside of render, then throwing a Promise if it's not already
loaded or unwrapping would treat it as if it wasn't there. Just like if
you rendered it in React. This lets you introspect what's inside which
isn't really something you should be able to do. This isn't compatible
with deprecating throwing-a-Promise and enable static compilation like
`use()` does. We'd have to deprecate `React.Children` before doing that
which we might anyway.
3) Wrap in a Fragment. If a Server Component was instead a Client
Component, you couldn't introspect through it anyway. Another
alternative might be to let it pass through but then it wouldn't be
given a flat key. We could also wrap it in a Fragment that is keyed.
That way you're always seeing an element. The issue with this solution
is that it wouldn't see the key of the Server Component since that gets
forwarded to the child that is yet to resolve. The nice thing about that
strategy is it doesn't depend on throw-a-Promise but it might not be
keyed correctly when things move.
DiffTrain build for [9e7944f67c](https://github.com/facebook/react/commit/9e7944f67c72b9a69a8db092ba6bd99fe9c731e2)
A Flight Server can be a consumer of a stream from another Server. In
this case the meta data is attached to debugInfo properties on lazy,
Promises, Arrays or Elements that might in turn get forwarded to the
next stream. In this case we want to forward this debug information to
the client in the stream.
I also added a DEV only `environmentName` option to the Flight Server.
This lets you name the server that is producing the debug info so that
you can trace the origin of where that component is executing. This
defaults to `"server"`. DevTools could use this for badges or different
colors.
DiffTrain build for [629541bcc0](https://github.com/facebook/react/commit/629541bcc09fc7c0cc5c257541d084ee27457512)
In #28123 I switched these to be lazy references. However that creates a
lazy wrapper even if they're synchronously available. We try to as much
as possible preserve the original data structure in these cases.
E.g. here in the dev outlining I only use a lazy wrapper if it didn't
complete synchronously:
https://github.com/facebook/react/pull/28272/files#diff-d4c9c509922b3671d3ecce4e051df66dd5c3d38ff913c7a7fe94abc3ba2ed72eR638
Unfortunately we don't have a data structure that tracks the status of
each emitted row. We could store the task in the map but then they
couldn't be GC:ed as they complete. We could maybe store the status of
each element but seems so heavy.
For now I just went back to direct reference which might be an issue
since it can suspend something higher up when deduped.
DiffTrain build for [ba5e6a8329](https://github.com/facebook/react/commit/ba5e6a8329c7194a2c573c037a37f24ce45ee58f)
We could in theory actually support this case by throwing a Promise when
it's used inside a render. Allowing it to be synchronously unwrapped.
However, it's a bit sketchy because we officially only support this in
the render's child position or in `use()`.
Another alternative could be to actually pass the Promise/Lazy to the
callback so that you can reason about it and just return it again or
even unwrapping with `use()` - at least for the forEach case maybe.
DiffTrain build for [e41ee9ea70](https://github.com/facebook/react/commit/e41ee9ea70f8998144fdd959ac11fd7a40e4ee20)
This adds a new DEV-only row type `D` for DebugInfo. If we see this in
prod, that's an error. It can contain extra debug information about the
Server Components (or Promises) that were compiled away during the
server render. It's DEV-only since this can contain sensitive
information (similar to errors) and since it'll be a lot of data, but
it's worth using the same stream for simplicity rather than a
side-channel.
In this first pass it's just the Server Component's name but I'll keep
adding more debug info to the stream, and it won't always just be a
Server Component's stack frame.
Each row can get more debug rows data streaming in as it resolves and
renders multiple server components in a row.
The data structure is just a side-channel and it would be perfectly fine
to ignore the D rows and it would behave the same as prod. With this
data structure though the data is associated with the row ID / chunk, so
you can't have inline meta data. This means that an inline Server
Component that doesn't get an ID otherwise will need to be outlined. The
way I outline Server Components is using a direct reference where it's
synchronous though so on the client side it behaves the same (i.e.
there's no lazy wrapper in this case).
In most cases the `_debugInfo` is on the Promises that we yield and we
also expose this on the `React.Lazy` wrappers. In the case where it's a
synchronous render it might attach this data to Elements or Arrays
(fragments) too.
In a future PR I'll wire this information up with Fiber to stash it in
the Fiber data structures so that DevTools can pick it up. This property
and the information in it is not limited to Server Components. The name
of the property that we look for probably shouldn't be `_debugInfo`
since it's semi-public. Should consider the name we use for that.
If it's a synchronous render that returns a string or number (text node)
then we don't have anywhere to attach them to. We could add a
`React.Lazy` wrapper for those but I chose to prioritize keeping the
data structure untouched. Can be useful if you use Server Components to
render data instead of React Nodes.
DiffTrain build for [b229f540e2](https://github.com/facebook/react/commit/b229f540e2da91370611945f9875e00a96196df6)
Along with all the places using it like the `_debugSource` on Fiber.
This still lets them be passed into `createElement` (and JSX dev
runtime) since those can still be used in existing already compiled code
and we don't want that to start spreading to DOM attributes.
We used to have a DEV mode that compiles the source location of JSX into
the compiled output. This was nice because we could get the actual call
site of the JSX (instead of just somewhere in the component). It had a
bunch of issues though:
- It only works with JSX.
- The way this source location is compiled is different in all the
pipelines along the way. It relies on this transform being first and the
source location we want to extract but it doesn't get preserved along
source maps and don't have a way to be connected to the source hosted by
the source maps. Ideally it should just use the mechanism other source
maps use.
- Since it's expensive it only works in DEV so if it's used for
component stacks it would vary between dev and prod.
- It only captures the callsite of the JSX and not the stack between the
component and that callsite. In the happy case it's in the component but
not always.
Instead, we have another zero-cost trick to extract the call site of
each component lazily only if it's needed. This ensures that component
stacks are the same in DEV and PROD. At the cost of worse line number
information.
The better way to get the JSX call site would be to get it from `new
Error()` or `console.createTask()` inside the JSX runtime which can
capture the whole stack in a consistent way with other source mappings.
We might explore that in the future.
This removes source location info from React DevTools and React Native
Inspector. The "jump to source code" feature or inspection can be made
lazy instead by invoking the lazy component stack frame generation. That
way it can be made to work in prod too. The filtering based on file path
is a bit trickier.
When redesigned this UI should ideally also account for more than one
stack frame.
With this change the DEV only Babel transforms are effectively
deprecated since they're not necessary for anything.
DiffTrain build for [37d901e2b8](https://github.com/facebook/react/commit/37d901e2b81e12d40df7012c6f8681b8272d2555)
These used to be reserved props because the classic React.createElement
runtime passed this data as props, whereas the jsxDEV() runtime passes
them as separate arguments.
This brings us incrementally closer to being able to pass the props
object directly through to React instead of cloning a subset into a new
object.
The React.createElement runtime is unaffected.
DiffTrain build for [91caa96e42](https://github.com/facebook/react/commit/91caa96e4261704d42333f5e02ba32d870379fc4)
This used to be trivial but it's no longer trivial.
In Fizz and Fiber this is split into renderWithHooks and
finishFunctionComponent since they also support indeterminate
components.
Interestingly thanks to this unification we always call functions with
an arity of 2 which is a bit weird - with the second argument being
undefined in everything except forwardRef and legacy context consumers.
This makes Flight makes the same thing but we could also call it with an
arity of 1.
Since Flight errors early if you try to pass it a ref, and there's no
legacy context, the second arg is always undefined.
The practical change in this PR is that returning a Promise from a
forwardRef now turns it into a lazy. We previously didn't support async
forwardRef since it wasn't supported on the client. However, since
eventually this will be supported by child-as-a-promise it seems fine to
support it.
DiffTrain build for [f07ac1e268](https://github.com/facebook/react/commit/f07ac1e2680a26c5b3bf9c651d62c792de71d46d)
The JSX runtime (both the new one and the classic createElement runtime)
check for reserved props like `key` and `ref` by doing a lookup in a
plain object map with `hasOwnProperty`.
There are only a few reserved props so this inlines the checks instead.
DiffTrain build for [1beb94133a](https://github.com/facebook/react/commit/1beb94133a93a433669a893aef02dd5afec07394)
Every time we create a task we need to wait for it so we increase a ref
count. We can do this in `createTask`. This is in line with what Fizz
does too.
They differ in that Flight counts when they're actually flushed where as
Fizz decrements them when they complete.
Flight should probably count them when they complete so it's possible to
wait for the end before flushing for buffering purposes.
DiffTrain build for [0d11563b4a](https://github.com/facebook/react/commit/0d11563b4a96e0f4f2361cdf7375b12375688163)
Adds a feature flag to control whether the client cache function is just
a passthrough. before we land breaking changes for the next major it
will be off and then we can flag it on when we want to break it.
flag is off for OSS for now and on elsewhere (though the parent flag
enableCache is off in some cases)
DiffTrain build for [2bc7d336ae](https://github.com/facebook/react/commit/2bc7d336ae7db689699baeb1fffc2c03d8753ffe)
Conceptually a Server Component in the tree is the same as a Client
Component.
When we render a Server Component with a key, that key should be used as
part of the reconciliation process to ensure the children's state are
preserved when they move in a set. The key of a child should also be
used to clear the state of the children when that key changes.
Conversely, if a Server Component doesn't have a key it should get an
implicit key based on the slot number. It should not inherit the key of
its children since the children don't know if that would collide with
other keys in the set the Server Component is rendered in.
A Client Component also has an identity based on the function's
implementation type. That mainly has to do with the state (or future
state after a refactor) that Component might contain. To transfer state
between two implementations it needs to be of the same state type. This
is not a concern for a Server Components since they never have state so
identity doesn't matter.
A Component returns a set of children. If it returns a single child,
that's the same as returning a fragment of one child. So if you
conditionally return a single child or a fragment, they should
technically reconcile against each other.
The simple way to do this is to simply emit a Fragment for every Server
Component. That would be correct in all cases. Unfortunately that is
also unfortunate since it bloats the payload in the common cases. It
also means that Fiber creates an extra indirection in the runtime.
Ideally we want to fold Server Component aways into zero cost on the
client. At least where possible. The common cases are that you don't
specify a key on a single return child, and that you do specify a key on
a Server Component in a dynamic set.
The approach in this PR treats a Server Component that returns other
Server Components or Lazy Nodes as a sequence that can be folded away.
I.e. the parts that don't generate any output in the RSC payload.
Instead, it keeps track of their keys on an internal "context". Which
gets reset after each new reified JSON node gets rendered.
Then we transfer the accumulated keys from any parent Server Components
onto the child element. In the simple case, the child just inherits the
key of the parent.
If the Server Component itself is keyless but a child isn't, we have to
add a wrapper fragment to ensure that this fragment gets the implicit
key but we can still use the key to reset state. This is unusual though
because typically if you keyed something it's because it was already in
a fragment.
In the case a Server Component is keyed but forks its children using a
fragment, we need to key that fragment so that the whole set can move
around as one. In theory this could be flattened into a parent array but
that gets tricky if something suspends, because then we can't send the
siblings early.
The main downside of this approach is that switching between single
child and fragment in a Server Component isn't always going to reconcile
against each other. That's because if we saw a single child first, we'd
have to add the fragment preemptively in case it forks later. This
semantic of React isn't very well known anyway and it might be ok to
break it here for pragmatic reasons. The tests document this
discrepancy.
Another compromise of this approach is that when combining keys we don't
escape them fully. We instead just use a simple `,` separated concat.
This is probably good enough in practice. Additionally, since we don't
encode the implicit 0 index slot key, you can move things around between
parents which shouldn't really reconcile but does. This keeps the keys
shorter and more human readable.
DiffTrain build for [95ec128399](https://github.com/facebook/react/commit/95ec128399a8b34884cc6bd90a041e03ce5c1844)
Adds a new entrypoint for the production jsx-runtime when using
react-server condition. Currently the entrypoints are the same but in
the future we will potentially change the implementation of the runtime
in ways that can only be optimized for react-server constraints and we
want to have the entrypoint already separated so environments using it
will be pulling in the right version
DiffTrain build for [00f9acb12c](https://github.com/facebook/react/commit/00f9acb12c036ef24a2b6d7957d75359c6280087)
There's no need to separate strict mode from strict effects mode any
more.
I didn't clean up the `StrictEffectMode` fiber flag, because it's used
to prevent strict effects in legacy mode. I could replace those checks
with `LegacyMode` checks, but when we remove legacy mode, we can remove
that flag and condense them into one StrictMode flag away.
DiffTrain build for [3d1da1f9ab](https://github.com/facebook/react/commit/3d1da1f9ab7d54984c096e6a04c8729f3a50fd8a)
Semantically if you make your reason for aborting a Postpone instance
the render should not hit the error pathways but should instead follow
the postpone pathways. It's awkward today to actually get your hands on
a Postpone instance because you have to catch the throw from postpone
and then pass that into `abort()` or `AbortController.abort()`
(depending on the renderer API you are using)
This change makes it so that in most circumstances if you abort with a
postpone the `onPostpone` handler will be called and the Suspense
boundaries still pending will be put into client render mode with the
appropriate postpone digest to avoid trigger recoverable error pathways
on the client.
Similar to postponing in the shell during a resume or render however if
you abort before the shell is complete in a resume or render we will
fatally error. The fatal error is contextualized by React to avoid
passing the postpone object itself to the `onError` and related options.
DiffTrain build for [1219d57fc9](https://github.com/facebook/react/commit/1219d57fc9fcbf44c873c0b10e5acbd31f613c15)
Treat `<a href="" />` the same with and without
`enableFilterEmptyStringAttributesDOM`
in https://github.com/facebook/react/pull/18513 we started to warn and
ignore for empty `href` and `src` props since it usually hinted at a
mistake. However, for anchor tags there's a valid use case since `<a
href=""></a>` will by spec render a link to the current page. It could
be used to reload the page without having to rely on browser
affordances.
The implementation for Fizz is in the spirit of
https://github.com/facebook/react/pull/21153. I gated the fork behind
the flag so that the fork is DCE'd when the flag is off.
DiffTrain build for [f3ce87ab65](https://github.com/facebook/react/commit/f3ce87ab650f07774e1df9bc3f8033e023973d10)
Previously we only warned during a synchronous update, because we
eventually want to support async client components in controlled
scenarios, like during navigations. However, we're going to warn in all
cases for now until we figure out how that should work.
DiffTrain build for [178f435194](https://github.com/facebook/react/commit/178f4351947a842ff0b56700e9115b25ae8f20d0)
Updates Fizz to handle Hoistables (Resources and Elements) in a way that
better aligns with Suspense fallbacks
1. Hoistable Elements inside a fallback (regardless of how deep and how
many additional boundaries are intermediate) will be ignored. The
reasoning is fallbacks are transient and since there is not good way to
clean up hoistables because they escape their Suspense container its
better to not emit them in the first place. SSR fallbacks are already
not full fidelity because they never hydrate so this aligns with that
somewhat.
2. Hoistable stylesheets in fallbacks will only block the reveal of a
parent suspense boundary if the fallback is going to flush with that
completed parent suspense boundary. Previously if you rendered a
stylesheet Resource inside a fallback any parent suspense boundaries
that completed after the shell flushed would include that resource in
the set required to resolve before the boundary reveal happens on the
client. This is not a semantic change, just a performance optimization
3. preconnect and preload hoistable queues are gone, if you want to
optimize resource loading you shoudl use `ReactDOM.preconnect` and
`ReactDOM.preload`. `viewport` meta tags get their own queue because
they need to go before any preloads since they affect the media state.
In addition to those functional changes this PR also refactors the
boundary resource tracking by moving it to the task rather than using
function calls at the start of each render and flush. Tasks also now
track whether they are a fallback task
supercedes prior work here: https://github.com/facebook/react/pull/27534
DiffTrain build for [554fc49f41](https://github.com/facebook/react/commit/554fc49f41465d914b15dc8eb2ec094f37824f7e)
To make React.startTransition more consistent with the hook form of
startTransition, we capture errors thrown by the scope function and pass
them to the global reportError function. (This is also what we do as a
default for onRecoverableError.)
This is a breaking change because it means that errors inside of
startTransition will no longer bubble up to the caller. You can still
catch the error by putting a try/catch block inside of the scope
function itself.
We do the same for async actions to prevent "unhandled promise
rejection" warnings.
The motivation is to avoid a refactor hazard when changing from a sync
to an async action, or from useTransition to startTransition.
DiffTrain build for [60f190a559](https://github.com/facebook/react/commit/60f190a55948a7512d4e2a336f03b45fd38d6a80)
## Summary
In the precendences Map every key is prefixed with `p`. This fixes one
case where this is missing.
## How did you test this change?
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Demonstrate the code is solid. Example: The exact commands you ran and
their output, screenshots / videos if the pull request changes the user
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DiffTrain build for [763612647c](https://github.com/facebook/react/commit/763612647ceb66d95f728af896ca5e18a8181db8)
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