feat(core): Show unresolved promise origin in tests

[jespertheend]

No description provided.

[jespertheend]

It builds, but I'm running into a panic when it tries to find the stalled top level await.
It seems like find_stalled_top_level_await is not able to find anything and reaches the end of the function:

deno/core/runtime.rs

Line 1528 in b68f70c

unreachable!()

[bartlomieju]

Hey @jespertheend and sorry for slow response. I made a mistake when I suggested this solution - the hanging promises in the tests are not really top level so the suggested API will not work in this situation. I need to dig through V8 APIs to see if there's any other API we can use to actually get a stack trace for the promise (I believe not). If you wanna play around with it I suggest trying to manually reject the promise when you get into that resolve_value handler.

[jespertheend]

@bartlomieju Ah that's clever, that sounds like it could work. Though simply rejecting it seems to cause the promise to reject outside of the test. I'm getting This error was not caught from a test, even though I'm awaiting the promise inside the test. But maybe I'm not rejecting the promise the right way.

Deno.test({
  name: "Unresolved forever",
  async fn() {
    await new Promise(() => {});
  }
})

./my.test.js (uncaught error)
error: (in promise) undefined
This error was not caught from a test and caused the test runner to fail on the referenced module.
It most likely originated from a dangling promise, event/timeout handler or top-level code.

[bartlomieju]

It looks like there's no API to reject a promise from Rust API - we can only do that if we created the promise from Rust, but that's not the case here. You found a tough nut to crack @jespertheend! I need more time to think about the ways we could try to tackle it.

[jespertheend]

@bartlomieju Wait so does the code in my latest commit not reject the promise?
Because the console does print error: (in promise) undefined.

Would it be possible to attach a catch handler from rust and then get the stack from there?

[bartlomieju]

@jespertheend it's rejecting a "floating promise" that you added - so it still doesn't point which promise did hang and there's this additional message:

This error was not caught from a test and caused the test runner to fail on the referenced module.
It most likely originated from a dangling promise, event/timeout handler or top-level code.

that is not really actionable here.

Would it be possible to attach a catch handler from rust and then get the stack from there?

That's the problem - it looks like we can't do that since we only have access to v8::Promise and not v8::PromiseResolver