[Flight][Static] Implement halting a prerender behind enableHalt #30705
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It feels a little unnecessary/hacky to introduce another object kind with duck-typing especially if postpone is going away and then ideally thrown promises go away too.
How about instead we store the reason on the request like we do for fatalError and use it if we're in the halting status. It can even be the same slot with a different status (we already abuse it for aborting in the same way).
We are currently using that slot for the ref id. I could instead just always emit an infinite promise into those slots instead though rather than referring to the a shared one since it's basically the same size |
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enableHalt turns on a mode for flight prerenders where aborts are treated like infinitely stalled outcomes while still completing the prerender. For regular tasks we simply serialize the slot as a promise that never settles. For ReadableStream, Blob, and Async Iterators we just never advance the serialization so they remain unfinished when consumed on the client. When enableHalt is turned on aborts of prerenders will halt rather than error. The abort reason is forwarded to the upstream produces of the aforementioned async iterators, blobs, and ReadableStreams. In the future if we expose a signal that you can consume from within a render to cancel additional work the abort reason will also be forwarded there
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| @@ -1798,6 +1818,7 @@ function serializeLazyID(id: number): string { | |||
| function serializeInfinitePromise(): string { | |||
| return '$@'; | |||
| } | |||
| const reusableInfinitePromiseModel = stringify(serializeInfinitePromise()); | |||
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Does this get inlined btw? Might as well just hard code the string to ensure it does. There's not really any purpose in having it be hoisted value since it'll be interned anyway.
| @@ -2202,6 +2232,9 @@ function renderModel( | |||
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| if (request.status === ABORTING) { | |||
| task.status = ABORTED; | |||
| if (enableHalt && request.fatalError === haltSymbol) { | |||
| return serializeInfinitePromise(); | |||
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So I don't think this is actually right. Because this is saying that this value will be a Promise but if this wasn't already a Promise that's incorrect. It's not the same as postpone which gets serialized as an error. What you want here is more like serializeByValueID to an ID that will never resolve.
The only time you can use serializeInfinitePromise() is when you're actually serializing a Promise/Thenable.
using infinitely suspending promises isn't right because this will parse as a promise which is only appropriate if the value we're halting at is a promise. Instead we need to have a special marker type that says this reference will never resolve. Additionally flight client needs to not error any halted references when the stream closes because they will otherwise appear as an error addresses: #30705 (comment)
**breaking change for canary users: Bumps peer dependency of React from `19.0.0-rc-1eaccd82-20240816` to `19.0.0-rc-eb3ad065-20240822`** No changes required in Next.js it seems. [diff facebook/react@1eaccd82...eb3ad065](facebook/react@1eaccd8...eb3ad06) <details> <summary>React upstream changes</summary> - facebook/react#30761 - facebook/react#30779 - facebook/react#30775 - facebook/react#30770 - facebook/react#30756 - facebook/react#30755 - facebook/react#30768 - facebook/react#30760 - facebook/react#30732 - facebook/react#30757 - facebook/react#30750 - facebook/react#30751 - facebook/react#30753 - facebook/react#30740 - facebook/react#30748 - facebook/react#30746 - facebook/react#30747 - facebook/react#30731 - facebook/react#30725 - facebook/react#30741 - facebook/react#30730 - facebook/react#30726 - facebook/react#30717 - facebook/react#30729 - facebook/react#30721 - facebook/react#30720 - facebook/react#30705 </details>
enableHalt turns on a mode for flight prerenders where aborts are treated like infinitely stalled outcomes while still completing the prerender. For regular tasks we simply serialize the slot as a promise that never settles. For ReadableStream, Blob, and Async Iterators we just never advance the serialization so they remain unfinished when consumed on the client.
When enableHalt is turned on aborts of prerenders will halt rather than error. The abort reason is forwarded to the upstream produces of the aforementioned async iterators, blobs, and ReadableStreams. In the future if we expose a signal that you can consume from within a render to cancel additional work the abort reason will also be forwarded there