1470558 - Debugger: provide detailed completion values for generator and async function suspensions

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P3)

Description

[Jason Orendorff [:jorendorff]]

When an async function call frame `return`s or `await`s, the debugger currently has no way to tell which.

Here's a script to dump the completion value passed to `onPop` when we call a simple async function:

----
let g = newGlobal();
g.eval(`
    async function f() {
        await "promise";
        return "done";
    }
`);

let dbg = new Debugger(g);
dbg.onEnterFrame = frame => {
    frame.onPop = completion => { print(uneval(completion)); };
};

g.f();
drainJobQueue();
----

The output is three lines:

----
({return:{}})
({return:"promise"})
({return:"done"})
----

The first `onPop` fires during the async function's "initial suspend". (I don't understand why we have to do this for async functions.) The return value is a Generator that's an implementation detail of the async function task.

The second `onPop` is for the `await`, and the third is for the `return`.

Comment 1

[Jason Orendorff [:jorendorff]]

The obvious fix would be to change await completions to look like `{await: <value>}`. It might break some existing code, though. :-\

Comment 2

[Jim Blandy :jimb]

Attachment: Bug 1470558: js::Debugger::slowPathOnLeaveFrame should always get a pc for non-WASM frames. r?jorendorff

Add an assertion.

Comment 3

[Jim Blandy :jimb]

Attachment: Bug 1470558: Debugger::slowPathOnLeaveFrame: move 'suspending' block a little later. r?jorendorff

Our ultimate goal in this bug is to include information about yields and awaits
in the completion value passed to the onPop handler. This means that detecting
when a frame is being suspended becomes just another step in building a
completion value. That change becomes a little clearer if those two steps happen
next to each other.

Depends on D24995

Comment 4

[Jim Blandy :jimb]

Attachment: Bug 1470558: Distinguish yields and awaits in completion values. r?jorendorff

Depends on D24996

Comment 5

[Jim Blandy :jimb]

I want to break that last patch up into smaller steps, but comments on the overall approach are welcome.

Comment 6

[Jim Blandy :jimb]

Attachment: Bug 1470558: js/src/vm/Debugger.h: Move forward declarations to top. r?jorendorff

Depends on D24996

Comment 7

[Jim Blandy :jimb]

Attachment: Bug 1470558: Use Completion type in DebuggerObject::{set,get}Property. r?jorendorff

Depends on D24997

Comment 8

[Jim Blandy :jimb]

Rebased patch queue.

Comment 9

[Jim Blandy :jimb]

Attachment: Bug 1470558: Use Completion type in Debugger::receiveCompletionValue. r?jorendorff

Replacing more calls to Debugger::resultToCompletion with uses of the newer API.

Comment 10

[Jim Blandy :jimb]

Attachment: Bug 1470558: Use Completion type for Debugger eval-related methods. r?jorendorff

DebuggerFrame::eval and DebuggerObject::evalInGlobal are two more invocation
functions that can reasonably use Completion to report the results of the
operation.

Depends on D33076

Comment 11

[Jim Blandy :jimb]

Attachment: Bug 1470558: Use Completion in Debugger.Object 'call' and 'apply' methods. r?jorendorff

Depends on D33077

Comment 12

[Jim Blandy :jimb]

Attachment: Bug 1470558: Delete Debugger::{resultToCompletion,newCompletionValue,receiveCompletionValue}. r?jorendorff

All uses of these have been rewritten to use the Completion type.

Depends on D33078

Comment 13

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1248eb8d570b
js::Debugger::slowPathOnLeaveFrame should always get a pc for non-WASM frames. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/69a369e2cdaa
Debugger::slowPathOnLeaveFrame: move 'suspending' block a little later. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/bb62c9157f04
js/src/vm/Debugger.h: Move forward declarations to top. r=jorendorff

Comment 14

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/1248eb8d570b
https://hg.mozilla.org/mozilla-central/rev/69a369e2cdaa
https://hg.mozilla.org/mozilla-central/rev/bb62c9157f04

Comment 15

[Marco Mucci [:MarcoM]]

Marking leave-open as there are patches that still need to be land.

Comment 16

[Jim Blandy :jimb]

Oh dear. Completion can't be passed directly as a parameter. I'll need to rework some of these interfaces.

Comment 17

[Jim Blandy :jimb]

If we can land bug 1563065, the interfaces can remain unchanged.

Comment 18

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c4bae8a5a111
Distinguish yields and awaits in completion values. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/abdfe0ed8ea1
Use Completion type in DebuggerObject::{set,get}Property. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/6791d671e6cc
Use Completion type in Debugger::receiveCompletionValue. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/6034237161dc
Use Completion type for Debugger eval-related methods. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/ef67e1b47f9c
Use Completion in Debugger.Object 'call' and 'apply' methods. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/1a18ccfcdc98
Delete Debugger::{resultToCompletion,newCompletionValue,receiveCompletionValue}. r=jorendorff

Comment 19

[Dorel Luca [:dluca]]

Backed out 6 changesets (bug 1470558) for Build bustage in js/src/vm/Debugger.cpp

Log:
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=255140151&repo=autoland&lineNumber=48540

Push with failures:
https://treeherder.mozilla.org/#/jobs?repo=autoland&revision=1a18ccfcdc98eec64d8f76850713f0348cd073e5

Backout:
https://hg.mozilla.org/integration/autoland/rev/6a41c590899802f9636815ad69b14d67318582cf

Comment 20

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/f0aa53a43409
Distinguish yields and awaits in completion values. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/3f47b78ffdc0
Use Completion type in DebuggerObject::{set,get}Property. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/f82f7c40443d
Use Completion type in Debugger::receiveCompletionValue. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/4f26d027343a
Use Completion type for Debugger eval-related methods. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/3800d671c64e
Use Completion in Debugger.Object 'call' and 'apply' methods. r=jorendorff
https://hg.mozilla.org/integration/autoland/rev/483d687212fb
Delete Debugger::{resultToCompletion,newCompletionValue,receiveCompletionValue}. r=jorendorff

Comment 21

[Andrei Ciure[:aciure]]

https://hg.mozilla.org/mozilla-central/rev/f0aa53a43409
https://hg.mozilla.org/mozilla-central/rev/3f47b78ffdc0
https://hg.mozilla.org/mozilla-central/rev/f82f7c40443d
https://hg.mozilla.org/mozilla-central/rev/4f26d027343a
https://hg.mozilla.org/mozilla-central/rev/3800d671c64e
https://hg.mozilla.org/mozilla-central/rev/483d687212fb