1636691 - Improve stack information for promises due to exception in then/catch handlers

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Tom S]

It seems like we just drop the exception stack when a promise resolve/reject callback throws. In particular MaybeGetAndClearException just ignores the exception stack. Instead we should probably propagate that stack through various Promise methods.

Compare

js> Promise.reject("foobar")
js> quit()
Unhandled rejection: "foobar"
Stack:
  @typein:1:9

and

js> Promise.resolve().then(() => { throw "foobar"; })
js> quit()
Unhandled rejection: "foobar"
(no stack trace available)

Comment 2

[Tom S]

Attachment: Bug 1636691 - Use pending exception stack as rejection stack for Promises. r?arai<Paste>

We already have the pending exception stack, we might as well use it.
This helps in cases where we reject the promises but the current stack is already empty again.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/2b2753c09568
Use pending exception stack as rejection stack for Promises. r=arai<Paste>

Comment 4

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/2b2753c09568