This is intended to be used by various client side resources where the
transfer size is interesting to know how it'll perform in various
network conditions. Not intended to be added by the server.
For now it's only added internally by DevTools itself on img/css but
I'll add it from Flight Client too in a follow up.
This now shows this as the "transfer size" which is the encoded body
size + headers/overhead. Where as the "fileSize" that I add to images is
the decoded body size, like what you'd see on disk. This is what Chrome
shows so it's less confusing if you compare Network tab and this view.
We currently only track the reason something might suspend in
development mode through debug info but this excludes some cases. As a
result we can end up with boundary that suspends but has no cause. This
tries to detect that and show a notice for why that might be. I'm also
trying to make it work with old React versions to cover everything.
In production we don't track any of this meta data like `_debugInfo`,
`_debugThenable` etc. so after resolution there's no information to take
from. Except suspensey images / css which we can track in prod too. We
could track lazy component types already. We'd have to add something
that tracks after the fact if something used a lazy child, child as a
promise, hooks, etc. which doesn't exist today. So that's not backwards
compatible and might add some perf/memory cost. However, another
strategy is also to try to replay the components after the fact which
could be backwards compatible. That's tricky for child position since
there's so many rules for how to do that which would have to be
replicated.
If you're in development you get a different error. Given that we've
added instrumentation very recently. If you're on an older development
version of React, then you get a different error. Unfortunately I think
my feature test is not quite perfect because it's tricky to test for the
instrumentation I just added.
https://github.com/facebook/react/pull/34146 So I think for some
prereleases that has `_debugOwner` but doesn't have that you'll get a
misleading error.
Finally, if you're in a modern development environment, the only reason
we should have any gaps is because of throw-a-Promise. This will
highlight it as missing. We can detect that something threw if a
Suspense boundary commits with a RetryCache but since it's a WeakSet we
can't look into it to see anything about what it might have been. I
don't plan on doing anything to improve this since it would only apply
to new versions of React anyway and it's just inherently flawed. So just
deprecate it #34032.
Note that nothing in here can detect that we suspended Transition. So
throwing at the root or in an update won't show that anywhere.
This computes a min and max range for the whole suspense boundary even
when selecting a single component so that each component in a boundary
has a consistent range.
The start of this range is the earliest start of I/O in that boundary or
the end of the previous suspense boundary, whatever is earlier. If the
end of the previous boundary would make the range large, then we cap it
since it's likely that the other boundary was just an independent
render.
The end of the range is the latest end of I/O in that boundary. If this
is smaller than the end of the previous boundary plus the 300ms
throttle, then we extend the end. This visualizes what throttling could
potentially do if the previous boundary committed right at its end. Ofc,
it might not have committed exactly at that time in this render. So this
is just showing a potential throttle that could happen. To see actual
throttle, you look in the Performance Track.
<img width="661" height="353" alt="Screenshot 2025-08-14 at 12 41 43 AM"
src="https://github.com/user-attachments/assets/b0155e5e-a83f-400c-a6b9-5c38a9d8a34f"
/>
We could come up with some annotation to highlight that this is eligible
to be throttled in this case. If the lines don't extend to the edge,
then it's likely it was throttled.
Same as #34166 but for Suspensey images.
The trick here is to check the `SuspenseyImagesMode` since not all
versions of React and not all subtrees will have Suspensey images
enabled yet.
The other trick is to read back from `currentSrc` to get the image url
we actually resolved to in this case. Similar to how for Suspensey CSS
we check if the media query would've matched.
<img width="591" height="205" alt="Screenshot 2025-08-11 at 9 32 56 PM"
src="https://github.com/user-attachments/assets/ac98785c-d3e0-407c-84e0-c27f86c0ecac"
/>
The skeletons right now are too jarring because they're visually heavier
than the content that comes in later. This makes them draw attention to
themselves as flashing things.
A good skeleton and loading indicator should ideally start as invisible
as possible and then gradually become more visible the longer time
passes so that if it loads quickly then it was never much visible at
all.
Even at its max it should never be heavier weight than the final content
so that it visually reverts into lesser. Another rule of thumb is that
it should be as close as possible to the final content in size but if
it's unknown it should always be smaller than the final content so that
the content grows into its slot rather than the slot contracting.
This makes the skeleton fade from invisible into the dimmest color just
as a subtle hint that something is still loading.
I also added a missing skeleton since the stack traces in rendered by
can now suspend while source mapping.
The other tweak I did is use disabled buttons in all the cases where we
load the ability to enable a button. This is more subtle and if you
hover over you can see why it's still disabled. Rather than flashing the
button each time you change element.
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"
/>
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"
/>
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.
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.
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"
/>
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.
Follow up to #34050.
It's not actually possible to suspend *above* the root since even if you
suspend in the first child position, you're still suspending the
HostRoot which always has a corresponding FiberInstance and
SuspenseNode.
