Persistent renderers used the `Update` effect flag to check if a subtree
needs to be cloned. In some cases, that causes extra renders, such as
when a layout effect is triggered which only has an effect on the JS
side, but doesn't update the host components.
It's been a bit tricky to find the right places where this needs to be
set and I'm not 100% sure I got all the cases even though the tests
passed.
We use static dependency injection. We shouldn't use this dynamic
dependency injection we do for DevTools internals. There's also meta
programming like spreading and stuff that isn't needed.
This moves the config from `injectIntoDevTools` to the FiberConfig so it
can be statically resolved.
Closure Compiler has some trouble generating optimal code for this
anyway so ideally we'd refactor this further but at least this is better
and saves a few bytes and avoids some code paths (when minified).
This is not used by DevTools since it has its own implementation of it.
This function is getting removed since `findDOMNode` is getting removed
so we shouldn't keep around extra bytes unnecessarily.
There is also `findHostInstancesForRefresh` which should really be
implemented on the `react-refresh` side. Not using an injection but
that's a heavier lift and only affects `__DEV__`.
**This API is not intended to ship. This is a temporary unstable hook
for internal performance profiling.**
This PR exposes `unstable_useContextWithBailout`, which takes a compare
function in addition to Context. The comparison function is run to
determine if Context propagation and render should bail out earlier.
`unstable_useContextWithBailout` returns the full Context value, same as
`useContext`.
We can profile this API against `useContext` to better measure the cost
of Context value updates and gather more data around propagation and
render performance.
The bailout logic and test cases are based on
https://github.com/facebook/react/pull/20646
Additionally, this implementation allows multiple values to be compared
in one hook by returning a tuple to avoid requiring additional Context
consumer hooks.
This is a major nit but this avoids an extra stack frame when we're
replaying logs.
Normally the `printToConsole` frame doesn't show up because it'd be
ignore listed.
<img width="421" alt="Screenshot 2024-07-25 at 11 49 39 AM"
src="https://github.com/user-attachments/assets/81334c2f-e19e-476a-871e-c4db9dee294e">
When you expand to show ignore listed frames a ton of other frames show
up.
<img width="516" alt="Screenshot 2024-07-25 at 11 49 47 AM"
src="https://github.com/user-attachments/assets/2ab8bdfb-464c-408d-9176-ee2fabc114b6">
The annoying thing about this frame is that it's at the top of the stack
where as typically framework stuff ends up at the bottom and something
you can ignore. The user space stack comes first.
With this fix there's no longer any `printToConsole` frame.
<img width="590" alt="Screenshot 2024-07-25 at 12 09 09 PM"
src="https://github.com/user-attachments/assets/b8365d53-31f3-43df-abce-172d608d3c9c">
Am I wiling to eat the added complexity and slightly slower performance
for this nit? Definitely.
Following https://github.com/facebook/react/pull/30436
Concurrent by default strategy has been unshipped. Here we clean up the
`allowConcurrentByDefault` path and related logic/tests.
For now, this keeps the `concurrentUpdatesByDefaultOverride` argument in
`createContainer` and `createHydrationContainer` and ignores the value
to prevent more breaking changes to `react-reconciler` in the RC stage.
We still filter them before passing from server to client in Flight
Server but when presenting a native stack, we don't need to filter them.
That's left to ignore listing in the presentation.
The stacks are pretty clean regardless thanks to the bottom stack
frames.
We can also unify the owner stack formatters into one shared module
since Fizz/Flight/Fiber all do the same thing. DevTools currently does
the same thing but is forked so it can support multiple versions.
Concurrent by default has been unshipped! Let's clean it up.
Here we remove `forceConcurrentByDefaultForTesting`, which allows us to
run tests against both concurrent strategies. In the next PR, we'll
remove the actual concurrent by default code path.
Stacked on #30427.
Most hooks and such are called inside renders which already have these
on the stack but life-cycles that call out on them are useful to cut off
too.
Typically we don't create JSX in here so they wouldn't be part of owner
stacks anyway but they can be apart of plain stacks such as the ones
prefixes to console logs or printed by error dialogs.
This lets us cut off any React internals below. This should really be
possible using just ignore listing too ideally.
At this point we should maybe just build a Babel plugin that lets us
annotate a function to need to have this name.
Stacked on #30401.
Previously we were transferring the original V8 stack trace string to
the client and then parsing it there. However, really the server is the
one that knows what format it is and it should be able to vary by server
environment.
We also don't use the raw string anymore (at least not in
enableOwnerStacks). We always create the native Error stacks.
The string also made it unclear which environment it is and it was
tempting to just use it as is.
Instead I parse it on the server and make it a structured stack in the
transfer format. It also makes it clear that it needs to be formatted in
the current environment before presented.
Stacked on https://github.com/facebook/react/pull/30400 and
https://github.com/facebook/react/pull/30369
Previously we were using fake evals to recreate a stack for console
replaying and thrown errors. However, for owner stacks we just used the
raw string that came from the server.
This means that the format of the owner stack could include different
formats. Like Spidermonkey format for the client components and V8 for
the server components. This means that this stack can't be parsed
natively by the browser like when printing them as error like in
https://github.com/facebook/react/pull/30289. Additionally, since
there's no source file registered with that name and no source mapping
url, it can't be source mapped.
Before:
<img width="1329" alt="before-firefox"
src="https://github.com/user-attachments/assets/cbe03f9c-96ac-48fb-b58f-f3a224a774f4">
Instead, we need to create a fake stack like we do for the other things.
That way when it's printed as an Error it gets source mapped. It also
means that the format is consistently in the native format of the
current browser.
After:
<img width="753" alt="after-firefox"
src="https://github.com/user-attachments/assets/b436f1f5-ca37-4203-b29f-df9828c9fad3">
So this is nice because you can just take the result from
`captureOwnerStack()` and append it to an `Error` stack and print it
natively. E.g. this is what React DevTools will do.
If you want to parse and present it yourself though it's a bit awkward
though. The `captureOwnerStack()` API now includes a bunch of
`rsc://React/` URLs. These don't really have any direct connection to
the source map. Only the browser knows this connection from the eval.
You basically have to strip the prefix and then manually pass the
remainder to your own `findSourceMapURL`.
Another awkward part is that since Safari doesn't support eval sourceURL
exposed into `error.stack` - it means that `captureOwnerStack()` get an
empty location for server components since the fake eval doesn't work
there. That's not a big deal since these stacks are already broken even
for client modules for many because the `eval-source-map` strategy in
Webpack doesn't work in Safari for this same reason.
A lot of this refactoring is just clarifying that there's three kind of
ReactComponentInfo fields:
- `stack` - The raw stack as described on the original server.
- `debugStack` - The Error object containing the stack as represented in
the current client as fake evals.
- `debugTask` - The same thing as `debugStack` but described in terms of
a native `console.createTask`.
Ideally we wouldn't need to filter out React internals and it'd just be
covered by ignore listing by any downstream tool. E.g. a framework using
captureOwnerStack could have its own ignore listing. Printed owner
stacks would get browser source map ignore-listing. React DevTools could
have its own ignore list for internals. However, it's nice to be able to
provide nice owner stacks without a bunch of noise by default.
Especially on the server since they have to be serialized.
We currently call each function that calls into user space and track its
stack frame. However, this needs code for checking each one and doesn't
let us work across bundles.
Instead, we can name each of these frame something predictable by giving
the function a name.
Unfortunately, it's a common practice to rename functions or inline them
in compilers. Even if we didn't, others downstream from us or a dev-mode
minifier could. I use this `.bind()` trick to avoid minifying these
functions and ensure they get a unique name added to them in all
browsers. It's not 100% fool proof since a smart enough compiler could
also discover that the `this` value is not used and strip out the
function and then inline it but nobody does this yet at least.
This lets us find the bottom stack easily from stack traces just by
looking for the name.
Stacked on #30308.
This is now a noop module so we can stop applying the transform of
console.error using the Babel plugin in the mainline builds. I'm keeping
the transform for RN/WWW for now although it might be nice if the
transform moved into those systems as it gets synced instead of keeping
it upstream.
In jest tests we're already not running the forks for RN/WWW so we don't
need it at all there.
React transpiles some of its own `console.error` calls into a helper
that appends component stacks to those calls. However, this doesn't
cover user space `console.error` calls - which includes React helpers
that React has moved into third parties like createClass and prop-types.
The idea is that any user space component can add a warning just like
React can which is why React DevTools adds them too if they don't
already exist. Having them appended in both places is tricky because now
you have to know whether to remove them from React's logs.
Similarly it's often common for server-side frameworks to forget to
cover the `console.error` logs from other sources since React DevTools
isn't active there. However, it's also annoying to get component stacks
clogging the terminal - depending on where the log came from.
In the future `console.createTask()` will cover this use case natively
and when available we don't append them at all.
The new strategy relies on either:
- React DevTools existing to add them to React logs as well as third
parties.
- `console.createTask` being supported and surfaced.
- A third party framework showing the component stack either in an Error
Dialog or appended to terminal output.
For a third party to be able to implement this they need to be able to
get the component stack. To get the component stack from within a
`console.error` call you need to use the `React.captureOwnerStack()`
helper which is only available in `enableOwnerStacks` flag. However,
it's possible to polyfill with parent stacks using internals as a stop
gap. There's a question of whether React 19 should just go out with
`enableOwnerStacks` to expose this but regardless I think it's best it
doesn't include component stacks from the runtime for consistency.
In practice it's not really a regression though because typically either
of the other options exists and error dialogs don't implement
`console.error` overrides anyway yet. SSR terminals might miss them but
they'd only have them in DEV warnings to begin with an a subset of React
warnings. Typically those are either going to happen on the client
anyway or replayed.
Our tests are written to assert that component stacks work in various
scenarios all over the place. To ensure that this keeps working I
implement a "polyfill" that is similar to that expected a server
framework might do - in `assertConsoleErrorDev` and `toErrorDev`.
This PR doesn't yet change www or RN since they have their own forks of
consoleWithStackDev for now.
The full stack is the current execution stack (`new Error().stack`) +
the current owner stack (`React.captureOwnerStack()`).
The idea with the top frame was that when we append it to console.error
we'd include both since otherwise the true reason would be obscured
behind the little `>` to expand. So we'd just put both stack front and
center. By adding this into getCurrentStack it was easy to use the same
filtering. I never implemented in Fizz or Flight though.
However, with the public API `React.captureOwnerStack()` it's not
necessary to include the current stack since you already have it and
you'd have filtering capabilities in user space too.
Since I'm removing the component stacks from React itself we no longer
need this. It's expected that maybe RDT or framework polyfill would
include this same technique though.
While the goal is to remove legacy context completely, I think we can
already land the removal of legacy context for function components. I
didn't even know this feature existed until reading the code recently.
The win is just a couple of property lookups on function renders, but it
trims down the API already as the full removal will likely still take a
bit more time.
www: Starting with enabled test renderer and a feature flag for
production rollout.
RN: Not enabled, will follow up on this.
Object literals should be faster at least on React Native with Hermes as
the JS engine.
It might also be interesting to confirm the old comments in this file
from years ago are even still valid. Creating an object from a literal
should be a simpler operation.
It's a bit unfortunate that this introduces a bunch of copied code, but
since we rearely update the fields on fibers, this seems like an okay
tradeoff for a hot code path. An alternative would be some sort of macro
system, but that doesn't seem worth the extra complexity.
Currently we're printing parent stacks at the end of DOM nesting even
with owner stacks enabled. That's because the context of parent tree is
relevant for determining why two things are nested. It might not be
sufficient to see the owner stack alone.
I'm trying to get rid of parent stacks and rely on more of the plain
owner stacks or ideally console.createTask. These are generally better
anyway since the exact line for creating the JSX is available. It also
lets you find a parent stack frame that is most relevant e.g. if it's
hidden inside internals.
For DOM nesting there's really only two stacks that are relevant. The
creation of the parent and the creation of the child. Sometimes they're
close enough to be the same thing. Such as for parents that can't have
text children or when the ancestor is the direct parent created at the
same place (same owner).
Sometimes they're far apart. In this case I add a second console.error
within the context of the ancestor. That way the second stack trace can
be used to read the stack trace for where it was created.
To preserve some parent context I now print the parent stack in a diff
view format using the logic from hydration diffs. This includes some
siblings and props for context.
<img width="756" alt="Screenshot 2024-07-10 at 12 21 38 AM"
src="https://github.com/facebook/react/assets/63648/0843133d-cc7a-4ecc-91c0-f46ae8e99f20">
Text Nodes:
<img width="749" alt="Screenshot 2024-07-10 at 12 37 40 AM"
src="https://github.com/facebook/react/assets/63648/ee377d82-54ee-450a-99d1-fcc3ef290d59">
---------
Co-authored-by: tjallingt <tjallingt@gmail.com>
For environments that still have legacy contexts available, this adds a
warning to make the remaining call sites easier to locate and encourage
upgrades.
Only for parent stacks. This ensures that we can use the regular
mechanism for appending stack traces. E.g. you can polyfill it.
This is mainly so that I can later remove the automatic appending.
Component stacks have a similar problem to the problem with keyPath
where we had to move it down and set it late right before recursing.
Currently we work around that by popping exactly one off when something
suspends. That doesn't work with the new server stacks being added which
are more than one. It also meant that we kept having add a single frame
that could be popped when there shouldn't need to be one.
Unlike keyPath component stacks has this weird property that once
something throws we might need the stack that was attempted for errors
or the previous stack if we're going to retry and just recreate it.
I've tried a few different approaches and I didn't like either but this
is the one that seems least problematic.
I first split out renderNodeDestructive into a retryNode helper. During
retries only retryNode is called. When we first discover a node, we pass
through renderNodeDestructive.
Instead of add a component stack frame deep inside renderNodeDestructive
after we've already refined a node, we now add it before in
renderNodeDestructive. That way it's only added once before being
attempted. This is similar to how Fiber works where in ChildFiber we
match the node once to create the instance and then later do we attempt
to actually render it and it's only the second part that's ever retried.
This unfortunately means that we now have to refine the node down to
element/lazy/thenables twice. To avoid refining the type too I move that
to be done lazily.
This was missed in the mount dev dispatcher. It was only in the rerender
dispatcher which means that it was only logged during the rerender.
Since DevTools can hide logs during rerenders, this hid the warning in
StrictMode.
Stacked on #30170.
This lets us track Server Component parent stacks in Fizz which also
lets us track the correct owner stack for lazy.
In Fiber we're careful not to make any DEV only fibers but since the
ReactFizzComponentStack data structures just exist for debug meta data
anyway we can just expand on that.
Stacked on #30142.
This tracks owners and their stacks in DEV in Fizz. We use the
ComponentStackNode as the data structure to track this information -
effectively like ReactComponentInfo (Server) or Fiber (Client). They're
the instance.
I then port them same logic from ReactFiberComponentStack,
ReactFiberOwnerStack and ReactFiberCallUserSpace to Fizz equivalents.
This gets us both owner stacks from `captureOwnerStack()`, as well as
appended to console.errors logged by Fizz, while rendering and in
onError.
Follow up to #30105.
This supports `renderToMarkup` in a non-RSC environment (not the
`react-server` condition).
This is just a Fizz renderer but it errors at runtime when you use
state, effects or event handlers that would require hydration - like the
RSC version would. (Except RSC can give early errors too.)
To do this I have to move the `react-html` builds to a new `markup`
dimension out of the `dom-legacy` dimension so that we can configure
this differently from `renderToString`/`renderToStaticMarkup`.
Eventually that dimension can go away though if deprecated. That also
helps us avoid dynamic configuration and we can just compile in the
right configuration so the split helps anyway.
One consideration is that if a compiler strips out useEffects or inlines
initial state from useState, then it would not get called an the error
wouldn't happen. Therefore to preserve semantics, a compiler would need
to inject some call that can check the current renderer and whether it
should throw.
There is an argument that it could be useful to not error for these
because it's possible to write components that works with SSR but are
just optionally hydrated. However, there's also an argument that doing
that silently is too easy to lead to mistakes and it's better to error -
especially for the e-mail use case where you can't take it back but you
can replay a queue that had failures. There are other ways to
conditionally branch components intentionally. Besides if you want it to
be silent you can still use renderToString (or better yet
renderToReadableStream).
The primary mechanism is the RSC environment and the client-environment
is really the secondary one that's only there to support legacy
environments. So this also ensures parity with the primary environment.
This is all behind the `enableOwnerStacks` flag.
This is a follow up to #29088. In that I moved type validation into the
renderer since that's the one that knows what types are allowed.
However, I only removed it from `React.createElement` and not the JSX
which was an oversight.
However, I also noticed that for invalid types we don't have the right
stack trace for throws because we're not yet inside the JSX element that
itself is invalid. We should use its stack for the stack trace. That's
the reason it's enough to just use the throw now because we can get a
good stack trace from the owner stack. This is fixed by creating a fake
Throw Fiber that gets assigned the right stack.
Additionally, I noticed that for certain invalid types like the most
common one `undefined` we error in Flight so a missing import in RSC
leads to a generic error. Instead of erroring on the Flight side we
should just let anything that's not a Server Component through to the
client and then let the Client renderer determine whether it's a valid
type or not. Since we now have owner stacks through the server too, this
will still be able to provide a good stack trace on the client that
points to the server in that case.
<img width="571" alt="Screenshot 2024-06-25 at 6 46 35 PM"
src="https://github.com/facebook/react/assets/63648/6812c24f-e274-4e09-b4de-21deda9ea1d4">
To get the best stack you have to expand the little icon and the regular
stack is noisy [due to this Chrome
bug](https://issues.chromium.org/issues/345248263) which makes it a
little harder to find but once that's fixed it might be easier.
When we replay logs we badge them with e.g. `[Server]`. That way it's
easy to identify that the source of the log actually happened on the
Server (RSC). However, when we threw an error we didn't have any such
thing. The error was rethrown on the client and then handled just like
any other client error.
This transfers the `environmentName` in DEV to our restored Error
"sub-class" (conceptually) along with `digest`. That way you can read
`error.environmentName` to print this in your own UI.
I also updated our default for `onCaughtError` (and `onError` in Fizz)
to use the `printToConsole` helper that the Flight Client uses to log it
with the badge format. So by default you get the same experience as
console.error for caught errors:
<img width="810" alt="Screenshot 2024-06-10 at 9 25 12 PM"
src="https://github.com/facebook/react/assets/63648/8490fedc-09f6-4286-9332-fbe6b0faa2d3">
<img width="815" alt="Screenshot 2024-06-10 at 9 39 30 PM"
src="https://github.com/facebook/react/assets/63648/bdcfc554-504a-4b1d-82bf-b717e74975ac">
Unfortunately I can't do the same thing for `onUncaughtError` nor
`onRecoverableError` because they use `reportError` which doesn't have
custom formatting (unless we also prevented default on window.onerror).
However maybe that's ok because 1) you should always have an error
boundary 2) it's not likely that an RSC error can actually recover
because it's not going to be rendered again so shouldn't really happen
outside some parent conditionally rendering maybe.
The other problem with this approach is that the default is no longer
trivial - so reimplementing the default in user space is trickier and
ideally we shouldn't expose our default to be called.
Only with the enableOwnerStacks flag (which is not on in www).
This is a new DEV-only API to be able to implement what we do for
console.error in user space.
This API does not actually include the current stack that you'd get from
`new Error().stack`. That you'd have to add yourself.
This adds the ability to have conditional development exports because we
plan on eventually having separate ESM builds that use the "development"
or "production" export conditions.
NOTE: This removes the export of `act` from `react` in prod (as opposed
to a function that throws) - inline with what we do with other
conditional exports.
Stacked on #29807.
This lets the nearest Suspense/Error Boundary handle it even if that
boundary is defined by the model itself.
It also ensures that when we have an error during serialization of
properties, those can be associated with the nearest JSX element and
since we have a stack/owner for that element we can use it to point to
the source code of that line. We can't track the source of any nested
arbitrary objects deeper inside since objects don’t track their stacks
but close enough. Ideally we have the property path but we don’t have
that right now. We have a partial in the message itself.
<img width="813" alt="Screenshot 2024-06-09 at 10 08 27 PM"
src="https://github.com/facebook/react/assets/63648/917fbe0c-053c-4204-93db-d68a66e3e874">
Note: The component name (Counter) is lost in the first message because
we don't print it in the Task. We use `"use client"` instead because we
expect the next stack frame to have the name. We also don't include it
in the actual error message because the Server doesn't know the
component name yet. Ideally Client References should be able to have a
name. If the nearest is a Host Component then we do use the name though.
However, it's not actually inside that Component that the error happens
it's in App and that points to the right line number.
An interesting case is that if something that's actually going to be
consumed by the props to a Suspense/Error Boundary or the Client
Component that wraps them fails, then it can't be handled by the
boundary. However, a counter intuitive case might be when that's on the
`children` props. E.g.
`<ErrorBoundary>{clientReferenceOrInvalidSerialization}</ErrorBoundary>`.
This value can be inspected by the boundary so it's not safe to pass it
so if it's errored it is not caught.
## Implementation
The first insight is that this is best solved on the Client rather than
in the Server because that way it also covers Client References that end
up erroring.
The key insight is that while we don't have a true stack when using
`JSON.parse` and therefore no begin/complete we can still infer these
phases for Elements because the first child of an Element is always
`'$'` which is also a leaf. In depth first that's our begin phase. When
the Element itself completes, we have the complete phase. Anything in
between is within the Element.
Using this idea I was able to refactor the blocking tracking mechanism
to stash the blocked information on `initializingHandler` and then on
the way up do we let whatever is nearest handle it - whether that's an
Element or the root Chunk. It's kind of like an Algebraic Effect.
cc @unstubbable This is something you might want to deep dive into to
find more edge cases. I'm sure I've missed something.
---------
Co-authored-by: eps1lon <sebastian.silbermann@vercel.com>
Stacked on #29807.
Conceptually the error's owner/task should ideally be captured when the
Error constructor is called but neither `console.createTask` does this,
nor do we override `Error` to capture our `owner`. So instead, we use
the nearest parent as the owner/task of the error. This is usually the
same thing when it's thrown from the same async component but not if you
await a promise started from a different component/task.
Before this stack the "owner" and "task" of a Lazy that errors was the
nearest Fiber but if the thing erroring is a Server Component, we need
to get that as the owner from the inner most part of debugInfo.
To get the Task for that Server Component, we need to expose it on the
ReactComponentInfo object. Unfortunately that makes the object not
serializable so we need to special case this to exclude it from
serialization. It gets restored again on the client.
Before (Shell):
<img width="813" alt="Screenshot 2024-06-06 at 5 16 20 PM"
src="https://github.com/facebook/react/assets/63648/7da2d4c9-539b-494e-ba63-1abdc58ff13c">
After (App):
<img width="811" alt="Screenshot 2024-06-08 at 12 29 23 AM"
src="https://github.com/facebook/react/assets/63648/dbf40bd7-c24d-4200-81a6-5018bef55f6d">
Stacked on #29804.
Transferring of debugInfo was added in #28286. It represents the parent
stack between the current Fiber and into the next Fiber we're about to
create. I.e. Server Components in between. ~I don't love passing
DEV-only fields as arguments anyway since I don't trust closure to
remove unused arguments that way.~ EDIT: Actually it seems like closure
handled that just fine before which is why this is no change in prod.
Instead, I track it on the module scope. Notably with DON'T use
try/finally because if something throws we want to observe what it was
at the time we threw. Like the pattern we use many other places.
Now we can use this when we create the Throw Fiber to associate the
Server Components that were part of the parent stack before this error
threw. There by giving us the correct parent stacks at the location that
threw.
This lets us rethrow it in the conceptual place of the child.
There's currently a problem when we suspend or throw in the child fiber
reconciliation phase. This work is done by the parent component, so if
it suspends or errors it is as if that component errored or suspended.
However, conceptually it's like a child suspended or errored.
In theory any thing can throw but it is really mainly due to either
`React.lazy` (both in the element.type position and node position),
`Thenable`s or the `Thenable`s that make up `AsyncIterable`s.
Mainly this happens because a Server Component that errors turns into a
`React.lazy`. In practice this means that if you have a Server Component
as the direct child of an Error Boundary. Errors inside of it won't be
caught.
We used to have the same problem with Thenables and Suspense but because
it's now always nested inside an inner Offscreen boundary that shields
it by being one level nested. However, when we have raw Offscreen
(Activity) boundaries they should also be able to catch the suspense if
it's in a hidden state so the problem returns. This fixes it for thrown
promises but it doesn't fix it for SuspenseException. I'm not sure this
is even the right strategy for Suspense though. It kind of relies on the
node never actually mounting/committing.
It's conceptually a little tricky because the current component can
inspect the children and make decisions based on them. Such as
SuspenseList.
The other thing that this PR tries to address is that it sets the
foundation for dealing with error reporting for Server Components that
errored. If something client side errors it'll be a stack like Server
(DebugInfo) -> Fiber -> Fiber -> Server -> (DebugInfo) -> Fiber.
However, all error reporting relies on it eventually terminating into a
Fiber that is responsible for the error. To avoid having to fork too
much it would be nice if I could create a Fiber to associate with the
error so that even a Server component error in this case ultimately
terminates in a Fiber.