We need to track that Suspensey CSS (Host Resources) can contribute to
the loading state. We can pick up the start/end time from the
Performance Observer API since we know which resource was loaded.
If DOM nodes are not filtered there's a link to the `<link>` instance.
The `"awaited by"` stack is the callsite of the JSX creating the
`<link>`.
<img width="591" height="447" alt="Screenshot 2025-08-11 at 1 35 21 AM"
src="https://github.com/user-attachments/assets/63af0ca9-de8d-4c74-a797-af0a009b5d73"
/>
Inspecting the link itself:
<img width="592" height="344" alt="Screenshot 2025-08-11 at 1 31 43 AM"
src="https://github.com/user-attachments/assets/89603dbc-6721-4bbf-8b58-6010719b29e3"
/>
In this approach I only include it if the page currently matches the
media query. It might contribute in some other scenario but we're not
showing every possible state but every possible scenario that might
suspend if timing changes in the current state.
Stacked on #34148.
This picks up the stack for the await from the `use()` Hook if one was
used to get this async info.
When you select a component that used hooks, we already collect this
information.
If you select a Suspense boundary, this lazily invokes the first
component that awaited this data to inspects its hooks and produce a
stack trace for the use().
When all we have for the name is "Promise" I also use the name of the
first callsite in the stack trace if there's more than one. Which in
practice will be the name of the custom Hook that called it. Ideally
we'd use source mapping and ignore listing for this but that would
require suspending the display. We could maybe make the SuspendedByRow
wrapped in a Suspense boundary for this case.
<img width="438" height="401" alt="Screenshot 2025-08-10 at 10 07 55 PM"
src="https://github.com/user-attachments/assets/2a68917d-c27b-4c00-84aa-0ceb51c4e541"
/>
Similar to #34144 but for `use()`.
`use()` dependencies don't get added to the `fiber._debugInfo` set
because that just models the things blocking the children, and not the
Fiber component itself. This picks up any debug info from the thenable
state that we stashed onto `_debugThenableState` so that we know it used
`use()`.
<img width="593" height="425" alt="Screenshot 2025-08-09 at 4 03 40 PM"
src="https://github.com/user-attachments/assets/c7e06884-4efd-47fa-a76b-132935db6ddc"
/>
Without #34146 this doesn't pick up uninstrumented promises but after
it, it'll pick those up as well. An instrumented promise that doesn't
have anything in its debug info is not picked up. For example, if it
didn't depend on any I/O on the server.
This doesn't yet pick up the stack trace of the `use()` call. That
information is in the Hooks information but needs a follow up to extract
it.
E.g. if the owner is null or the same as current component and no stack.
This happens for example when you return a plain Promise in the child
position and inspect the component it was returned in since there's no
hook stack and the owner is the same as the instance itself so there's
nothing new to link to.
Before:
<img width="267" height="99" alt="Screenshot 2025-08-10 at 10 28 32 PM"
src="https://github.com/user-attachments/assets/23341ab2-2888-457d-a1d1-128f3e0bd5ec"
/>
After:
<img width="253" height="91" alt="Screenshot 2025-08-10 at 10 29 04 PM"
src="https://github.com/user-attachments/assets/b33bb38b-891a-4f46-bc16-15604b033cdb"
/>
In the case where a Promise is not cached, then the thenable state might
contain an older version. This version is the one that was actually
observed by the committed render, so that's the version we'll want to
inspect.
We used to not store the thenable state but now we have it on
`_debugThenableState` in DEV.
<img width="593" height="359" alt="Screenshot 2025-08-10 at 8 26 04 PM"
src="https://github.com/user-attachments/assets/51ee53f3-a31a-4e3f-a4cf-bb20b6efe0cb"
/>
Similar to #34137 but for Promises.
This lets us pick up the debug info from a raw Promise as a child which
is not covered by `_debugThenables`. Currently ChildFiber doesn't stash
its thenables so we can't pick them up from devtools after the fact
without some debug info added to the parent.
It also lets us track some approximate start/end time of use():ed
promises based on the first time we saw this particular Promise.
Normally, we pick up debug info from instrumented Promise or React.Lazy
while we're reconciling in ReactChildFiber when they appear in the child
position. We add those to the `_debugInfo` of the Fiber.
However, we don't do that for for Lazy in the Component type position.
Instead, we have to pick up the debug info from it explicitly in
DevTools. Likely this is the info added by #34137. Older versions
wouldn't be covered by this particular mechanism but more generally from
throwing a Promise.
<img width="592" height="449" alt="Screenshot 2025-08-08 at 11 32 33 PM"
src="https://github.com/user-attachments/assets/87211c64-a7df-47b7-a784-5cdc7c5fae16"
/>
This creates a debug info object for the React.lazy call when it's
called on the client. We have some additional information we can track
for these since they're created by React earlier.
We can track the stack trace where `React.lazy` was called to associate
it back to something useful. We can track the start time when we
initialized it for the first time and the end time when it resolves. The
name from the promise if available.
This data is currently only picked up in child position and not
component position. The component position is in a follow up.
<img width="592" height="451" alt="Screenshot 2025-08-08 at 2 49 33 PM"
src="https://github.com/user-attachments/assets/913d2629-6df5-40f6-b036-ae13631379b9"
/>
This begs for ignore listing in the front end since these stacks aren't
filtered on the server.
The name prop will be used in the Suspense tab to help identity a
boundary. Activity will also allow names. A custom component can be
identified by the name of the component but built-ins doesn't have that.
This PR adds it to the Components Tree View as well since otherwise you
only have the key to go on. Normally we don't add all the props to avoid
making this view too noisy but this is an exception along with key to
help identify a boundary quickly in the tree.
Unlike the SuspenseNode store, this wouldn't ever have a name inferred
by owner since that kind of context already exists in this view.
<img width="600" height="161" alt="Screenshot 2025-08-08 at 1 20 36 PM"
src="https://github.com/user-attachments/assets/fe50d624-887a-4b9d-9186-75f131f83195"
/>
I also made both the key and name prop searchable.
<img width="608" height="206" alt="Screenshot 2025-08-08 at 1 32 27 PM"
src="https://github.com/user-attachments/assets/d3502d9c-7614-45fc-b973-57f06dd9cddc"
/>
This shows the stack trace of the JSX at each level so now you can also
jump to the code location for the JSX callsite. The visual is similar to
the owner stacks with `createTask` except when you click the `<...>` you
jump to the Instance in the Components panel.
<img width="593" height="450" alt="Screenshot 2025-08-08 at 12 19 21 AM"
src="https://github.com/user-attachments/assets/dac35faf-9d99-46ce-8b41-7c6fe24625d2"
/>
I'm not sure it's really necessary to have all the JSX stacks of every
owner. We could just have it for the current component and then the rest
of the owners you could get to if you just click that owner instance.
As a bonus, I also use the JSX callsite as the fallback for the "View
Source" button. This is primarily useful for built-ins like `<div>` and
`<Suspense>` that don't have any implementation to jump to anyway. It's
useful to be able to jump to where a boundary was defined.
With RSC it's common to get React.lazy objects in the children position.
This first formats them nicely.
Then it adds introspection support for both lazy and elements.
Unfortunately because of quirks with the hydration mechanism we have to
expose it under the name `_payload` instead of something direct. Also
because the name "type" is taken we can't expose the type field on an
element neither. That whole algorithm could use a rewrite.
<img width="422" height="137" alt="Screenshot 2025-08-07 at 11 37 03 PM"
src="https://github.com/user-attachments/assets/a6f65f58-dbc4-4b8f-928b-d7f629fc51b2"
/>
<img width="516" height="275" alt="Screenshot 2025-08-07 at 11 36 36 PM"
src="https://github.com/user-attachments/assets/650bafdb-a633-4d78-9487-a750a18074ce"
/>
For JSX an alternative or additional feature might be instead to jump to
the first Instance that was rendered using that JSX. We know that based
on the equality of the memoizedProps on the Fiber. It's just a matter of
whether we do that eagerly or more lazily when you click but you may not
have a match so would be nice to indicate that before you click.
Follow up to #34093.
There's an issue where the skipFrames argument isn't part of the cache
key so the other parsers that expect skipping one frame might skip zero
and show the internal `fakeJSXDEV` callsite. Ideally we should include
the skipFrames as part of the cache key but we can also always just skip
one.
This ensures that if the name is set manually after the declaration,
then we get that name when we log the value. For example Node.js
`Response` is declared as `_Response` and then later assigned a new
name.
We should probably really serialize all static enumerable properties but
"name" is non-enumerable so it's still a special case.
Stacked on #34101.
This adds a badge to owners if they are different from the currently
selected component's environment.
<img width="590" height="566" alt="Screenshot 2025-08-04 at 5 15 02 PM"
src="https://github.com/user-attachments/assets/e898254f-1b4c-498e-8713-978d90545340"
/>
We also add one to the end of stack traces if the stack trace has a
different environment than the owner which can happen when you call a
function (without rendering a component) into a third party environment
but the owner component was in the first party.
One awkward thing is that Suspense boundaries are always in the client
environment so their Server Components are always badged.
For "render" and "commit" phases we don't give any specific stack atm.
This tries to always provide something useful to say the cause of the
render.
For normal renders this will now show the same thing as the "Event" and
"Update" entries already showed. We stash the task that was used for
those and use them throughout the render and commit phases.
For Suspense (Retry lane) and Idle (Offscreen lane), we don't have any
updates. Instead for those there's a component that left work behind in
previous passes. For those I use the debugTask of the `<Suspense>` or
`<Activity>` boundary to indicate that this was the root of the render.
Similarly when an Action is invoked on a `<form action={...}>` component
using the built-in submit handler, there's no actionable stack in user
space that called it. So we use the stack of the JSX for the form
instead.
If there is a commit that removes the currently inspected (selected)
elements in the Components tree, we are going to kick off the transition
to re-render the Tree. The elements will be re-rendered with the
previous inspectedElementID, which was just removed and all consecutive
calls to store object with this id would produce errors, since this
element was just removed.
We should handle store mutations synchronously. Doesn't make sense to
start a transition in this case, because Elements depend on the
TreeState and could make calls to store in render function.
Before:
<img width="2286" height="1734" alt="Screenshot 2025-08-06 at 17 41 14"
src="https://github.com/user-attachments/assets/97d92220-3488-47b2-aa6b-70fa39345f6b"
/>
After:
https://github.com/user-attachments/assets/3da36aff-6987-4b76-b741-ca59f829f8e6
Stacked on #34089.
This measures the client rects of the direct children of Suspense
boundaries as we reconcile. This will be used by the Suspense tab to
visualize the boundaries given their outlines.
We could ask for this more lazily just in case we're currently looking
at the Suspense tab. We could also do something like monitor the sizes
using a ResizeObserver to cover when they change.
However, it should be pretty cheap to this in the reconciliation phase
since we're already mostly visiting these nodes on the way down. We have
also already done all the layouts at this point since it was part of the
commit phase and paint already. So we're just reading cached values in
this phase. We can also infer that things are expected to change when
parents or sibling changes. Similar technique as ViewTransitions.
Stacked on #34093.
Instead of using the original `ReactStackTrace` that has the call sites
on the server, this parses the `Error` object which has the virtual call
sites on the client. We'll need this technique for things stack traces
suspending on the client anyway like `use()`.
We can then use these callsites to source map in the front end.
We currently don't source map function names but might be useful for
this use case as well as getting original component names from prod.
One thing this doesn't do yet is that it doesn't ignore list the stack
traces on the client using the source map's ignore list setting. It's
not super important since we expect to have already ignore listed on the
server but this will become important for client stack traces like
`use()`.
or end time if they have the same start time.
<img width="517" height="411" alt="Screenshot 2025-08-04 at 4 00 23 PM"
src="https://github.com/user-attachments/assets/b99be67b-5727-4e24-98c0-ee064fb21e2f"
/>
They would typically appear in this order naturally but not always.
Especially in Suspense boundaries where the order can also be depended
on when the components are discovered.
Stacked on #34094.
This shows the I/O stack if available. If it's not available or if it
has a different owner (like if it was passed in) then we show the
`"awaited at:"` stack below it so you can see where it started and where
it was awaited. If it's the same owner this tends to be unnecessary
noise. We could maybe be smarter if the stacks are very different then
you might want to show both even with the same owner.
<img width="517" height="478" alt="Screenshot 2025-08-04 at 11 57 28 AM"
src="https://github.com/user-attachments/assets/2dbfbed4-4671-4a5f-8e6e-ebec6fe8a1b7"
/>
Additionally, this adds an inferred await if there's no owner and no
stack for the await. The inferred await of a function/class component is
just the owner. No stack. Because the stack trace would be the return
value. This will also be the case if you use throw-a-Promise. The
inferred await in the child position of a built-in is the JSX location
of that await like if you pass a promise to a child. This inference
already happens when you pass a Promise from RSC so in this case it
already has an await - so this is mainly for client promises.
Stacked on #34082.
This keeps the DevToolsInstance children alive inside Offscreen trees
while they're hidden. However, they're sent as unmounted to the front
end store.
This allows DevTools state to be preserved between these two states.
Such as it keeps the "suspended by" set on the SuspenseNode alive since
the children are still mounted. So now you when you resuspend, you can
see what in the children was suspended. This is useful when you're
simulating a suspense but can also be a bit misleading when something
suspended for real since it'll only show the previous suspended set and
not what is currently suspending it since that hasn't committed yet.
SuspenseNodes inside resuspended trees are now kept alive too. That way
they can contribute to the timeline even when resuspended. We can choose
whether to keep them visible in the rects while hidden or not.
In the future we'll also need to add more special cases around Activity.
Because right now if SuspenseNodes are kept alive in the Suspense tab UI
while hidden, then they're also alive inside Activity that are hidden
which maybe we don't want. Maybe simplest would be that they both
disappear from the Suspense tab UI but can be considered for the
timeline.
Another case is that when Activity goes hidden, Fiber will no longer
cause its content to suspend the parent but that's not modeled here. So
hidden Activity will show up as "suspended by" in a parent Suspense.
When they disconnect, they should really be removed from the "suspended
by" set of the parent (and perhaps be shown only on the Activity
boundary itself).
This searches through the remaining children to see if any of them were
children of the bailed out FiberInstance and if so we should reuse them
in the new set. It's faster to do this than search through children of
the FiberInstance for Suspense boundaries.
Show the value as "fulfilled: Type" or "rejected: Type" immediately
instead of having to expand it twice. We could show all the properties
of the object immediately like we do in the Performance Track but it's
not always particularly interesting data in the value that isn't already
in the header.
I also moved it to the end after the stack traces since I think the
stack is more interesting but I'm also visually trying to connect the
stack trace with the "name" since typically the "name" will come from
part of the stack trace.
Before:
<img width="517" height="433" alt="Screenshot 2025-08-03 at 11 39 49 PM"
src="https://github.com/user-attachments/assets/ad28d8a2-c149-4957-a393-20ff3932a819"
/>
After:
<img width="520" height="476" alt="Screenshot 2025-08-03 at 11 58 35 PM"
src="https://github.com/user-attachments/assets/53a755b0-bb68-4305-9d16-d6fac7ca4910"
/>
We'll need complete parsing of stack traces for both owner stacks and
async debug info so we need to expand the stack parsing capabilities a
bit. This refactors the source location extraction to use some helpers
we can use for other things too.
This is a fork of `ReactFlightStackConfigV8` which also supports
DevTools requirements like checking both `react_stack_bottom_frame` and
`react-stack-bottom-frame` as well as supporting Firefox stacks.
It also supports extracting the first frame of a component stack or the
last frame of an owner stack for the source location.
We have two type of links that appear next to each other now. One type
of link jumps to a Component instance in the DevTools. The other opens a
source location - e.g. in your editor.
This clarifies that something will jump to the Component instance by
marking it as bold and using angle brackets around the name.
This can be seen in the "rendered by" list of owner as well as in the
async stack traces when the stack was in a different owner than the one
currently selected.
<img width="516" height="387" alt="Screenshot 2025-08-03 at 11 27 38 PM"
src="https://github.com/user-attachments/assets/5da50262-1e74-4e46-a6f8-96b4c1e4db31"
/>
The idea is to connect this styling to the owner stacks using
`createTask` where this same pattern occurs (albeit the task name is not
clickable):
<img width="454" height="188" alt="Screenshot 2025-08-03 at 11 23 45 PM"
src="https://github.com/user-attachments/assets/81a55c8f-963a-4fda-846a-97f49ef0c469"
/>
In fact, I was going to add the stack traces to the "rendered by" list
to give the ability to jump to the JSX location in the owner stack so
that it becomes this same view.
This has been bothering me. You can click the arrow and the value to
expand/collapse a KeyValue row but not the name.
When the name is not editable it should be clickable. Such as when
inspecting a Promise value.
The only thing that uses `memoizedState` as a public API is
ClassComponents. Everything else uses it as internals. We shouldn't ever
show those internals.
Before those internals showed up for example on a suspended Suspense
boundary:
<img width="436" height="370" alt="Screenshot 2025-08-03 at 8 13 37 PM"
src="https://github.com/user-attachments/assets/7fe275a7-d5da-421d-a000-523825916630"
/>
Fixes#33534.
`.then` method can be tested when you await a value that's not a
Promise. For regular Client References we have a way to mark those as
"async" and yield a reference to the unwrapped value in case it's a
Promise on the Client.
However, the realization is that we never serialize Promises as opaque
when passed from the client to the server. If a Promise is passed, then
it would've been deserialized as a Promise (while still registered as a
temporary reference) and not one of these Proxy objects.
Technically it could be a non-function value on the client which would
be wrong but you're not supposed to dot into it in the first place.
So we can just assume it's `undefined`.
<!--
Thanks for submitting a pull request!
We appreciate you spending the time to work on these changes. Please
provide enough information so that others can review your pull request.
The three fields below are mandatory.
Before submitting a pull request, please make sure the following is
done:
1. Fork [the repository](https://github.com/facebook/react) and create
your branch from `main`.
2. Run `yarn` in the repository root.
3. If you've fixed a bug or added code that should be tested, add tests!
4. Ensure the test suite passes (`yarn test`). Tip: `yarn test --watch
TestName` is helpful in development.
5. Run `yarn test --prod` to test in the production environment. It
supports the same options as `yarn test`.
6. If you need a debugger, run `yarn test --debug --watch TestName`,
open `chrome://inspect`, and press "Inspect".
7. Format your code with
[prettier](https://github.com/prettier/prettier) (`yarn prettier`).
8. Make sure your code lints (`yarn lint`). Tip: `yarn linc` to only
check changed files.
9. Run the [Flow](https://flowtype.org/) type checks (`yarn flow`).
10. If you haven't already, complete the CLA.
Learn more about contributing:
https://reactjs.org/docs/how-to-contribute.html
-->
## Summary
Fixes `await`-ing and returning temporary references in `async`
functions. These two operations invoke `.then()` under the hood if it is
available, which currently results in an "Cannot access then on the
server. You cannot dot into a temporary client reference..." error. This
can easily be reproduced by returning a temporary reference from a
server function.
Fixes#33534
## How did you test this change?
I added a test in a new test file. I wasn't sure where else to put it.
<img width="771" height="138" alt="image"
src="https://github.com/user-attachments/assets/09ffe6eb-271a-4842-a9fe-c68e17b3fb41"
/>
<!--
Demonstrate the code is solid. Example: The exact commands you ran and
their output, screenshots / videos if the pull request changes the user
interface.
How exactly did you verify that your PR solves the issue you wanted to
solve?
If you leave this empty, your PR will very likely be closed.
-->
We try to merge consecutive reactive scopes that will always invalidate
together, but there's one common case that isn't handled.
```js
const y = [[x]];
```
Here we'll create two consecutive scopes for the inner and outer array
expressions. Because the input to the second scope is a temporary,
they'll merge into one scope.
But if we name the inner array, the merging stops:
```js
const array = [x];
const y = [array];
```
This is because the merging logic checks if all the dependencies of the
second scope are outputs of the first scope, but doesn't account for
renaming due to LoadLocal/StoreLocal. The fix is to track these
temporaries.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/34049).
* __->__ #34049
* #34047
* #34044
Fixes remaining issue in #32261, where passing a previously useMemo()-d
value to `Object.entries()` makes the compiler think the value is
mutated and fail validatePreserveExistingMemo. While I was there I added
Object.keys() and Object.values() too.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/34047).
* #34049
* __->__ #34047
* #34044
The `waitForReference` call for debug info can trigger inside a
different object's initializingHandler. In that case, we can get
confused by which one is the root object.
We have this special case to detect if the initializing handler's object
is `null` and we have an empty string key, then we should replace the
root object's value with the resolved value.
52612a7cbd/packages/react-client/src/ReactFlightClient.js (L1374)
However, if the initializing handler actually should have the value
`null` then we might get confused by this and replace it with the
resolved value from a debug object. This fixes it by just using a
non-empty string as the key for the waitForReference on debug value
since we're not going to use it anyway.
It used to be impossible to get into this state since a `null` value at
the root couldn't have any reference inside itself but now the debug
info for a `null` value can have outstanding references.
However, a better fix might be using a placeholder marker object instead
of null or better yet ensuring that we know which root we're
initializing in the debug model.
This currently throws an invariant which may be misleading. I checked
the ecma262 spec and used the same list of reserved words in our check.
To err on the side of being conservative, we also error when strict mode
reserved words are used.
This was a pretty glaring memory leak. 🙈
I forgot to clean up the VirtualInstances from the id map so the Server
Component instances always leaked in DEV.
This is modeling Offscreen boundaries as the thing that unmounts a tree
in the frontend. This will let us model this as a "hide" that preserves
state instead in a follow up but not yet.
By doing it this way, we don't have to special case suspended Suspense
boundaries, at least not for the modern versions that use Offscreen as
the internal node. It's still special cased for the old React versions.
Instead, this is handled by the Offscreen fiber getting hidden.
By giving this fiber an FilteredFiberInstance, we also have somewhere to
store the children on (separately from the parent children set which can
include other siblings too like the loading state).
One consequence is that Activity boundary content now disappears when
they're hidden which is probably a good thing since otherwise it would
be confusing and noisy when it's used to render multiple pages at once.
