AbortSignal.any() assertion failure

[vinhill]

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What is the issue with the DOM Standard?

In Gecko Bug 1903676, a test case was found where the assertion in create a dependent abort signal step 4.2.1. does not hold. I believe this is a spec issue.

Here is the example

let a = new AbortController();
let b = AbortSignal.any([a.signal]);
a.signal.addEventListener("abort", () => {
  AbortSignal.any([b]);
  console.log(b.aborted, a.signal.aborted);  // false, true
})
a.abort();

During the abort event of a, we create a dependent signal from b, which is not yet aborted. If b is not aborted and dependent on a, the spec expects a to be not aborted too and asserts this. The problem is that signal abort fires the event before aborting the dependent signals, steps 5 and 6 of signal abort could be switched to resolve this issue.

@shaseley