This adds a "suspended by" row for each chunk that is referenced from a
client reference. So when you select a client component, you can see
what bundles will block that client component when loading on the
client.
This is only done in the browser build since if we added it on the
server, it would show up as a blocking resource and while it's possible
we expect that a typical server request won't block on loading JS.
<img width="664" height="486" alt="Screenshot 2025-08-17 at 3 45 14 PM"
src="https://github.com/user-attachments/assets/b1f83445-2a4e-4470-9a20-7cd215ab0482"
/>
<img width="745" height="678" alt="Screenshot 2025-08-17 at 3 46 58 PM"
src="https://github.com/user-attachments/assets/3558eae1-cf34-4e11-9d0e-02ec076356a4"
/>
Currently this is only included if it ends up wrapped in a lazy like in
the typical type position of a Client Component, but there's a general
issue that maybe hard references need to transfer their debug info to
the parent which can transfer it to the Fiber.
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.
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.
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"
/>
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.
Stacked on #34016.
This is using the same thing we already do for the performance track to
provide a description of the I/O based on the content of the resolved
Promise. E.g. a Response's URL.
<img width="375" height="388" alt="Screenshot 2025-07-28 at 1 09 49 AM"
src="https://github.com/user-attachments/assets/f3fdc40f-4e21-4e83-b49e-21c7ec975137"
/>
There's a lot of overlap between `enableComponentPerformanceTrack` and
`enableAsyncDebugInfo` because they both rely on timing information. The
former is mainly emit timestamps for how long server components and
awaits took. The latter how long I/O took.
`enableAsyncDebugInfo` is currently primarily for the component
performance track but its meta data is useful for other debug tools too.
This promotes that flag to stable.
However, `enableComponentPerformanceTrack` needs more work due to
performance concerns with Chrome DevTools so I need to separate them.
This keeps doing most of the timing tracking on the server but doesn't
emit the per-server component time stamps when
`enableComponentPerformanceTrack` is false.
Chrome DevTools Extensions has a silly problem where they block access
to load Resources from all protocols except [an allow
list](eb970fbc64/front_end/models/extensions/ExtensionServer.ts (L60)).
https://issues.chromium.org/issues/416196401
Even though these are `eval()` and not actually loaded from the network
they're blocked. They can really be any string. We just have to pick one
of:
```js
'http:', 'https:', 'file:', 'data:', 'chrome-extension:', 'about:'
```
That way React DevTools extensions can load this content to source map
them.
Webpack has the same issue with its `webpack://` and
`webpack-internal://` urls.
This resolves an outstanding issue where it was possible for debug info
and console logs to become out of order if they up blocked. E.g. by a
future reference or a client reference that hasn't loaded yet. Such as
if you console.log a client reference followed by one that doesn't. This
encodes the order similar to how the stream chunks work.
This also blocks the main chunk from resolving until the last debug info
has fully loaded, including future references and client references.
This also ensures that we could send some of that data in a different
stream, since then it can come out of order.
React Elements reference debug data (their stack and owner) in the debug
channel. If the debug channel isn't wired up this can block the client
from resolving.
We can infer that if there's no debug channel wired up and the reference
wasn't emitted before the element, then it's probably because it's in
the debug channel. So we can skip it.
This should also apply to debug chunks but they're not yet blocking
until #33665 lands.
This lets us pass a writable on the server side and readable on the
client side to send debug info through a separate channel so that it
doesn't interfere with the main payload as much. The main payload refers
to chunks defined in the debug info which means it's still blocked on it
though. This ensures that the debug data has loaded by the time the
value is rendered so that the next step can forward the data.
This will be a bit fragile to race conditions until #33665 lands.
Another follow up needed is the ability to skip the debug channel on the
receiving side. Right now it'll block forever if you don't provide one
since we're blocking on the debug data.
If we have the ability to lazy load Promise values, i.e. if we have a
debug channel, then we should always use it for Promises that aren't
already resolved and instrumented.
There's little downside to this since they're async anyway.
This also lets us avoid adding `.then()` listeners too early. E.g. if
adding the listener would have side-effect. This avoids covering up
"unhandled rejection" errors. Since if we listen to a promise eagerly,
including reject listeners, we'd have marked that Promise's rejection as
handled where as maybe it wouldn't have been otherwise.
In this mode we can also indefinitely wait for the Promise to resolve
instead of just waiting a microtask for it to resolve.
When a debug channel is available, we now allow objects to be lazily
requested though the debug channel and only then will the server send
it.
The client will actually eagerly ask for the next level of objects once
it parses its payload. That way those objects have likely loaded by the
time you actually expand that deep e.g. in the console repl. This is
needed since the console repl is synchronous when you ask it to invoke
getters.
Each level is lazily parsed which means that we don't parse the next
level even though we eagerly loaded it. We parse it once the getter is
invoked (in Chrome DevTools you have to click a little `(...)` to invoke
the getter). When the getter is invoked, the chunk is initialized and
parsed. This then causes the next level to be asked for through the
debug channel. Ensuring that if you expand one more level you can do so
synchronously.
Currently debug chunks are eagerly parsed, which means that if you have
things like server component props that are lazy they can end up being
immediately asked for, but I'm trying to move to make the debug chunks
lazy.
Stacked on #33718. Alternative to #33716.
The issue with flushing the Server Components track in its current form
is that we need to decide how long to wait before flushing whatever we
have. That's because the root's end time will be determined by the end
time of that last child.
However, if a child isn't actually used then we don't necessarily need
to include it in the Server Components track since it wasn't blocking
the initial render.
This waits for 100ms after the last pending chunk is resolved and if
nothing is invoking any more lazy initializers after that then we log
the Server Components track with the information we have at that point.
We also don't eagerly initialize any chunks that wasn't already
initialized so if nothing was rendered, then nothing will be logged.
This is somewhat an artifact of the current visualization. If we did
another transposed form we wouldn't necessarily need to wait until the
end and can log things as they're discovered.
When we have a debug channel open that can ask for more objects. That
doesn't close until all lazy objects have been explicitly asked for. If
you GC an object before the lazy references inside of it before asking
for or releasing the objects, then it'll never close.
This ensures that if there are no more PendingChunk and no more
ResolvedModelChunk then we can close the connection.
There's two sources of retaining the Response object. On one side we
have a handle to it from the stream coming from the server. On the other
side we have a handle to it from ResolvedModelChunk to ask for more data
when we lazily parse a model.
This PR makes a weak handle from the stream to the Response. However, it
keeps a strong reference alive whenever we're waiting on a pending chunk
because then the stream might be the root if the only listeners are the
callbacks passed to the promise and no references to the promise itself.
The pending chunks count can end up being zero even if we might get more
data because the references might be inside lazy chunks. In this case
the lazy chunks keeps the Response alive. When the lazy chunk gets
parsed it can find more chunks that then end up pending to keep the
response strongly alive until they resolve.
If a FlightClient runs inside a FlightServer like fetching from a third
party and that logs, then we currently double badge them since we just
add on another badge. The issue is that this might be unnecessarily
noisy but we also transfer the original format of the current server
into the second badge.
This extracts our own badge and then adds the environment name as
structured data which lets the client decide how to format it.
Before:
<img width="599" alt="Screenshot 2025-07-02 at 2 30 07 PM"
src="https://github.com/user-attachments/assets/4bf26a29-b3a8-4024-8eb9-a3f90dbff97a"
/>
After:
<img width="590" alt="Screenshot 2025-07-02 at 2 32 56 PM"
src="https://github.com/user-attachments/assets/f06bbb6d-fbb1-4ae6-b0e3-775849fe3c53"
/>
It's useful to be able to distinguish between different invocations of
common helper libraries (like fetch) without having to click through
each one.
This adds a heuristic to extract a useful description of I/O from the
Promise value. We try to find things like getUser(id) -> User where
User.id is the id or fetch(url) -> Response where Response.url is the
url.
For urls we use the filename (or hostname if there is none) as the short
name if it can fit. The full url is in the tooltip.
<img width="845" alt="Screenshot 2025-06-27 at 7 58 20 PM"
src="https://github.com/user-attachments/assets/95f10c08-13a8-449e-97e8-52f0083a65dc"
/>
<img width="634" alt="Screenshot 2025-06-27 at 1 13 20 PM"
src="https://github.com/user-attachments/assets/dc8c488b-4a23-453f-918f-36b245364934"
/>
We have to be careful with performance in DEV. It can slow down DX since
these are ran whether you're currently running a performance trace or
not. It can also show up as misleading since these add time to the
"Remaining Effects" entry.
I'm not adding all props to the entries. Instead, I'm only adding the
changed props after diffing and none for initial mount. I'm trying to as
much as possible pick a fast path when possible. I'm also only logging
this for the "render" entries and not the effects. If we did something
for effects, it would be more like checking with dep changed.
This could still have a negative effect on dev performance since we're
now also using the slower `performance.measure` API when there's a diff.
`react-stack-bottom-frame` -> `react_stack_bottom_frame`.
This survives `@babel/plugin-transform-function-name`, but now frames
will be displayed as `at Object.react_stack_bottom_frame (...)` in V8.
Checks that were relying on exact function name match were updated to
use either `.indexOf()` or `.includes()`
For backwards compatibility, both React DevTools and Flight Client will
look for both options. I am not so sure about the latter and if React
version is locked.
We generally treat these types of fields as optional on ReactDebugInfo
and should on ReactElement too.
That way we can consume prod payloads from third parties.
Stacked on #33666.
If we ever get a future reference to a cycle and that reference gets
eagerly parsed before the target has loaded then we can end up with a
cycle that never gets resolved. That's because our cycle resolution only
works if the cyclic future reference is created synchronously within the
parsing path of the child.
I haven't been able to construct a normal scenario where this would
break. So this doesn't fail any tests. However, I can construct it with
debug info since those are eagerly evaluated. It's also a prerequisite
if the debug data can come out of order, like if it's on a different
stream.
The fix here is to make all the internal dependencies in the "listener"
list into introspectable objects instead of closures. That way we can
traverse the list of dependencies of a blocked reference to see if it
ends up in a cycle and therefore skip the reference.
It would be nice to address this once and for all to be more resilient
to server changes, but I'm not sure if it's worth this complexity and
the extra CPU cost of tracing the dependencies. Especially if it's just
for debug data.
closes#32316fixesvercel/next.js#72104
---------
Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
This writes all debug info to a separate priority queue. In the future
I'll put this on a different channel.
Ideally I think we'd put it in the bottom of the stream but because it
actually blocks the elements from resolving anyway it ends up being
better to put them ahead. At least for now.
When we have two separate channels it's not possible to rely on the
order for consistency Even then we might write to that queue first for
this reason. We can't rely on it though. Which will show up like things
turning into Lazy instead of Element similar to how outlining can.
<img width="926" alt="Screenshot 2025-06-25 at 1 02 14 PM"
src="https://github.com/user-attachments/assets/1877d13d-5259-4cc4-8f48-12981e3073fe"
/>
The I/O entry doesn't show as aborted in the Server Request track
because technically it wasn't. The end time is just made up. It's still
going. It's not aborted until the abort signal propagates and if we do
get that signal wired up before it emits, it instead would show up as
rejected.
---------
Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
This is using the same trick as #30798 but for runtime code too. It's
essential zero cost.
This lets us include a source location for parent stacks of Server
Components when it has an owned child's location. Either from JSX or
I/O.
Ironically, a Component that throws an error will likely itself not get
the stack because it won't have any JSX rendered yet.
This adds plumbing for opening a stream from the Flight Client to the
Flight Server so it can ask for more data on-demand. In this mode, the
Flight Server keeps the connection open as long as the client is still
alive and there's more objects to load. It retains any depth limited
objects so that they can be asked for later. In this first PR it just
releases the object when it's discovered on the server and doesn't
actually lazy load it yet. That's coming in a follow up.
This strategy is built on the model that each request has its own
channel for this. Instead of some global registry. That ensures that
referential identity is preserved within a Request and the Request can
refer to previously written objects by reference.
The fixture implements a WebSocket per request but it doesn't have to be
done that way. It can be multiplexed through an existing WebSocket for
example. The current protocol is just a Readable(Stream) on the server
and WritableStream on the client. It could even be sent through a HTTP
request body if browsers implemented full duplex (which they don't).
This PR only implements the direction of messages from Client to Server.
However, I also plan on adding Debug Channel in the other direction to
allow debug info (optionally) be sent from Server to Client through this
channel instead of through the main RSC request. So the `debugChannel`
option will be able to take writable or readable or both.
---------
Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
This frees some memory that will be even more important in a follow up.
Currently, all `ReactPromise` instances hold onto their original
`Response`. The `Response` holds onto all objects that were in that
response since they're needed in case the parsed content ends up
referring to an existing object. If everything you retain are plain
objects then that's fine and the `Response` gets GC:ed, but if you're
retaining a `Promise` itself then it holds onto the whole `Response`.
The only thing that needs this reference at all is a
`ResolvedModelChunk` since it will lazily initialize e.g. by calling
`.then` on itself and so we need to know where to find any sibling
chunks it may refer to. However, we can just store the `Response` on the
`reason` field for this particular state.
That way when all lazy values are touched and initialized the `Response`
is freed. We also free up some memory by getting rid of the extra field.
Stacked on #33588, #33589 and #33590.
This lets us automatically show the resolved value in the UI.
<img width="863" alt="Screenshot 2025-06-22 at 12 54 41 AM"
src="https://github.com/user-attachments/assets/a66d1d5e-0513-4767-910c-5c7169fc2df4"
/>
We can also show rejected I/O that may or may not have been handled with
the error message.
<img width="838" alt="Screenshot 2025-06-22 at 12 55 06 AM"
src="https://github.com/user-attachments/assets/e0a8b6ae-08ba-46d8-8cc5-efb60956a1d1"
/>
To get this working we need to keep the Promise around for longer so
that we can access it once we want to emit an async sequence. I do this
by storing the WeakRefs but to ensure that the Promise doesn't get
garbage collected, I keep a WeakMap of Promise to the Promise that it
depended on. This lets the VM still clean up any Promise chains that
have leaves that are cleaned up. So this makes Promises live until the
last Promise downstream is done. At that point we can go back up the
chain to read the values out of them.
Additionally, to get the best possible value we don't want to get a
Promise that's used by internals of a third-party function. We want the
value that the first party gets to observe. To do this I had to change
the logic for which "await" to use, to be the one that is the first
await that happened in user space. It's not enough that the await has
any first party at all on the stack - it has to be the very first frame.
This is a little sketchy because it relies on the `.then()` call or
`await` call not having any third party wrappers. But it gives the best
object since it hides all the internals. For example when you call
`fetch()` we now log that actual `Response` object.
This adds better support for serializing class instances as Debug
values.
It adds a new marker on the object `{ "": "$P...", ... }` which
indicates which constructor's prototype to use for this object's
prototype. It doesn't encode arbitrary prototypes and it doesn't encode
any of the properties on the prototype. It might get some of the
properties from the prototype by virtue of `toString` on a `class`
constructor will include the whole class's body.
This will ensure that the instance gets the right name in logs.
Additionally, this now also invokes getters if they're enumerable on the
prototype. This lets us reify values that can only be read from native
classes.
---------
Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
We already support serializing the values of instrumented Promises as
debug values such as in console logs. However, we don't support plain
native promises.
This waits a microtask to see if we can read the value within a
microtask and if so emit it. This is so that we can still close the
connection.
Otherwise, we emit a "halted" row into its row id which replaces the old
"Infinite Promise" reference.
We could potentially wait until the end of the render before cancelling
so that if it resolves before we exit we can still include its value but
that would require a bit more work. Ideally we'd have a way to get these
lazily later anyway.
It turns out this was being compiled to a `_defineProperty` helper by
Babel or Closure. We're supposed to have it error the build when we use
features like this that might get compiled.
We should stick to simple ES5 features.
Stacked on #33539.
Stores dedupes of `renderConsoleValue` in a separate set. This allows us
to dedupe objects safely since we can't write objects using this
algorithm if they might also be referenced by the "real" serialization.
Also renamed it to `renderDebugModel` since it's not just for console
anymore.
On pages that have a high number of server components (e.g. common when
doing syntax highlighting), the debug outlining can produce extremely
large RSC payloads. For example a documentation page I was working on
had a 13.8 MB payload. I noticed that a majority of this was the source
code for the same function components repeated over and over again (over
4000 times) within `$E()` eval commands.
This PR deduplicates the same functions by serializing by reference,
similar to what is already done for objects. Doing this reduced the
payload size of my page from 13.8 MB to 4.6 MB, and resulted in only 31
evals instead of over 4000. As a result it reduced development page load
and hydration time from 4 seconds to 1.5 seconds. It also means the
deserialized functions will have reference equality just as they did on
the server.
Stacked on #33482.
There's a flaw with getting information from the execution context of
the ping. For the soft-deprecated "throw a promise" technique, this is a
bit unreliable because you could in theory throw the same one multiple
times. Similarly, a more fundamental flaw with that API is that it
doesn't allow for tracking the information of Promises that are already
synchronously able to resolve.
This stops tracking the async debug info in the case of throwing a
Promise and only when you render a Promise. That means some loss of data
but we should just warn for throwing a Promise anyway.
Instead, this also adds support for tracking `use()`d thenables and
forwarding `_debugInfo` from then. This is done by extracting the info
from the Promise after the fact instead of in the resolve so that it
only happens once at the end after the pings are done.
This also supports passing the same Promise in multiple places and
tracking the debug info at each location, even if it was already
instrumented with a synchronous value by the time of the second use.
Previously you weren't guaranteed to have only advancing time entries,
you could jump back in time, but now it omits unnecessary duplicates and
clamps automatically if you emit a previous time entry to enforce
forwards order only.
The reason I didn't do this originally is because `await` can jump in
the order because we're trying to encode a graph into a flat timeline
for simplicity of the protocol and consumers.
```js
async function a() {
await fetch1();
await fetch2();
}
async function b() {
await fetch3();
}
async function foo() {
const p = a();
await b();
return p;
}
```
This can effectively create two parallel sequences:
```
--1.................----2.......--
------3......---------------------
```
This can now be flattened to either:
```
--1.................3---2.......--
```
Or:
```
------3......1......----2.......--
```
Depending on which one we visit first. Regardless, information is lost.
I'd say that the second one is worse encoding of this scenario because
it pretends that we weren't waiting for part of the timespan that we
were. To solve this I think we should probably make `emitAsyncSequence`
create a temporary flat list and then sort it by start time before
emitting.
Although we weren't actually blocked since there was some CPU time that
was able to proceed to get to 3. So maybe the second one is actually
better. If we wanted that consistently we'd have to figure out what the
intersection was.
---------
Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>
Technically the async call graph spans basically all the way back to the
start of the app potentially, but we don't want to include everything.
Similarly we don't want to include everything from previous components
in every child component. So we need some heuristics for filtering out
data.
We roughly want to be able to inspect is what might contribute to a
Suspense loading sequence even if it didn't this time e.g. due to a race
condition.
One flaw with the previous approach was that awaiting a cached promise
in a sibling that happened to finish after another sibling would be
excluded. However, in a different race condition that might end up being
used so I wanted to include an empty "await" in that scenario to have
some association from that component.
However, for data that resolved fully before the request even started,
it's a little different. This can be things that are part of the start
up sequence of the app or externally cached data. We decided that this
should be excluded because it doesn't contribute to the loading sequence
in the expected scenario. I.e. if it's cached. Things that end up being
cache misses would still be included. If you want to test externally
cached data misses, then it's up to you or the framework to simulate
those. E.g. by dropping the cache. This also helps free up some noise
since static / cached data can be excluded in visualizations.
I also apply this principle to forwarding debug info. If you reuse a
cached RSC payload, then the Server Component render time and its awaits
gets clamped to the caller as if it has zero render/await time. The I/O
entry is still back dated but if it was fully resolved before we started
then it's completely excluded.
I noticed that the ThirdPartyComponent in the fixture was showing the
wrong stack and the `"use third-party"` is in the wrong location.
<img width="628" alt="Screenshot 2025-06-06 at 11 22 11 PM"
src="https://github.com/user-attachments/assets/f0013380-d79e-4765-b371-87fd61b3056b"
/>
When creating the initial JSX inside the third party server, we should
make sure that it has no owner. In a real cross-server environment you
get this by default by just executing in different context. But since
the fixture example is inside the same AsyncLocalStorage as the parent
it already has an owner which gets transferred. So we should make sure
that were we create the JSX has no owner to simulate this.
When we then parse a null owner on the receiving side, we replace its
owner/stack with the owner/stack of the call to `createFrom...` to
connect them. This worked fine with only two environments. The bug was
that when we did this and then transferred the result to a third
environment we took the original parsed stack trace. We should instead
parse a new one from the replaced stack in the current environment.
The second bug was that the `"use third-party"` badge ends up in the
wrong place when we do this kind of thing. Because the stack of the
thing entering the new environment is the call to `createFrom...` which
is in the old environment even though the component itself executes in
the new environment. So to see if there's a change we should be
comparing the current environment of the task to the owner's environment
instead of the next environment after the task.
After:
<img width="494" alt="Screenshot 2025-06-07 at 1 13 28 AM"
src="https://github.com/user-attachments/assets/e2e870ba-f125-4526-a853-bd29f164cf09"
/>
Reverts #33457, #33456 and #33442.
There are too many issues with wrappers, lazy init, stateful modules,
duplicate instantiation of async_hooks and duplication of code.
Instead, we'll just do a wrapper polyfill that uses Node Streams
internally.
I kept the client indirection files that I added for consistency with
the server though.
Follow up to #33442. This is the bundled version.
To keep type check passes from exploding and the maintainance of the
annoying `paths: []` list small, this doesn't add this to flow type
checks. We might miss some config but every combination should already
be covered by other one passes.
I also don't add any jest tests because to test these double export
entry points we need conditional importing to cover builds and
non-builds which turns out to be difficult for the Flight builds so
these aren't covered by any basic build tests.
This approach is what I'm going for, for the other bundlers too.
Stacked on #33403.
When a Promise is coming from React such as when it's passed from
another environment, we should forward the debug information from that
environment. We already do that when rendered as a child.
This makes it possible to also `await promise` and have the information
from that instrumented promise carry through to the next render.
This is a bit tricky because the current protocol is that we have to
read it from the Promise after it resolves so it has time to be assigned
to the promise. `async_hooks` doesn't pass us the instance (even though
it has it) when it gets resolved so we need to keep it around. However,
we have to be very careful because if we get this wrong it'll cause a
memory leak since we retain things by `asyncId` and then manually listen
for `destroy()` which can only be called once a Promise is GC:ed, which
it can't be if we retain it. We have to therefore use a `WeakRef` in
case it never resolves, and then read the `_debugInfo` when it resolves.
We could maybe install a setter or something instead but that's also
heavy.
The other issues is that we don't use native Promises in
ReactFlightClient so our instrumented promises aren't picked up by the
`async_hooks` implementation and so we never get a handle to our
thenable instance. To solve this we can create a native wrapper only in
DEV.
