Normative: make Promise.try use PromiseResolve in non-error case

[bakkot]

Using PromiseResolve differs from the current behavior in that when the argument returns a Promise whose .constructor is whatever the this value of the Promise.try call is¹, we just return that Promise directly instead of wrapping it in a new one. Otherwise it's exactly the same.

This has the advantage of better matching the intuition that this is for cases where you want to write Promise.resolve(foo()) but you also want to wrap sync errors in rejected Promises. Now it actually works exactly like

try {
  result = Promise.resolve(foo());
} catch (e) {
  result = Promise.reject(e);
}

As a bonus, it also means this costs zero microtask ticks in the case where the argument is actually an async function, instead of (as currently) two.

See matrix chat 1 2.

Footnotes

1. Precise check might change. ↩

[github-actions]

The rendered spec preview for this PR is available as a single page at https://tc39.es/ecma262/pr/3883 and as multiple pages at https://tc39.es/ecma262/pr/3883/multipage .