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export function isHangingPromiseRejectionError(
err: unknown
): err is HangingPromiseRejectionError {
if (typeof err !== 'object' || err === null || !('digest' in err)) {
return false
}
return err.digest === HANGING_PROMISE_REJECTION
}
const HANGING_PROMISE_REJECTION = 'HANGING_PROMISE_REJECTION'
class HangingPromiseRejectionError extends Error {
public readonly digest = HANGING_PROMISE_REJECTION
constructor(public readonly expression: string) {
super(
`During prerendering, ${expression} rejects when the prerender is complete. Typically these errors are handled by React but if you move ${expression} to a different context by using \`setTimeout\`, \`after\`, or similar functions you may observe this error and you should handle it in that context.`
)
}
}
type AbortListeners = Array<(err: unknown) => void>
const abortListenersBySignal = new WeakMap<AbortSignal, AbortListeners>()
/**
* This function constructs a promise that will never resolve. This is primarily
* useful for cacheComponents where we use promise resolution timing to determine which
* parts of a render can be included in a prerender.
*
* @internal
*/
export function makeHangingPromise<T>(
signal: AbortSignal,
expression: string
): Promise<T> {
if (signal.aborted) {
return Promise.reject(new HangingPromiseRejectionError(expression))
} else {
const hangingPromise = new Promise<T>((_, reject) => {
const boundRejection = reject.bind(
null,
new HangingPromiseRejectionError(expression)
)
let currentListeners = abortListenersBySignal.get(signal)
if (currentListeners) {
currentListeners.push(boundRejection)
} else {
const listeners = [boundRejection]
abortListenersBySignal.set(signal, listeners)
signal.addEventListener(
'abort',
() => {
for (let i = 0; i < listeners.length; i++) {
listeners[i]()
}
},
{ once: true }
)
}
})
// We are fine if no one actually awaits this promise. We shouldn't consider this an unhandled rejection so
// we attach a noop catch handler here to suppress this warning. If you actually await somewhere or construct
// your own promise out of it you'll need to ensure you handle the error when it rejects.
hangingPromise.catch(ignoreReject)
return hangingPromise
}
}
function ignoreReject() {}
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