Fix panic on "unreachable code" that is reachable

[dralley]

Fixes servo/servo#22580

[dralley]

According to the discussion on the linked issue, cancellation became supported in this issue servo/servo#22367

This is my first servo PR :)

[Manishearth]

This isn't the correct fix, these items are not supposed to appear in the timeline, they get dealt with during insertion. The correct fix is to move this return to the outer if https://github.com/dralley/media/blob/d06aac618ed1884eb4a5d0b64a86bd371a60017f/audio/param.rs#L210

[Manishearth]

(we haven't implemented the difference between Cancel and CancelHold correctly, but that's for another time.)

[dralley]

@Manishearth I'm still getting the issue - is this patch what you had in mind or did I move it to the wrong place?

[dralley]

[dalley@localhost servo]$ ./mach run https://midi.city
%c * Tone.js r7 * 
background: #000; color: #fff
internal error: entered unreachable code: CancelScheduledValues/SetValue should never appear in the timeline (thread AudioRenderThread, at /home/dalley/Devel/servo-dev/media/audio/param.rs:333)
stack backtrace:

[dralley]

Prints nothing

[Manishearth]

@dralley Are you sure it's been recompiled using your local branch? I don't see how this is possible at all.

[dralley]

@Manishearth yup I'm sure

[dalley@localhost servo]$ ./mach build --dev
   Compiling servo-media-audio v0.1.0 (/home/dalley/Devel/servo-dev/media/audio)
   Compiling servo-media v0.1.0 (https://github.com/servo/media#ecd5a7c6)

With a debug at the very top, it does print this

[dalley@localhost servo]$ ./mach run https://midi.city
[/home/dalley/Devel/servo-dev/media/audio/param.rs:182] ":?" = ":?"
[/home/dalley/Devel/servo-dev/media/audio/param.rs:182] &event = SetValue(
    0.0,
)
%c * Tone.js r7 * 
background: #000; color: #fff
[/home/dalley/Devel/servo-dev/media/audio/param.rs:182] ":?" = ":?"
[/home/dalley/Devel/servo-dev/media/audio/param.rs:182] &event = CancelScheduledValues(
    Tick(
        128,
    ),
)
internal error: entered unreachable code: CancelScheduledValues/SetValue should never appear in the timeline (thread AudioRenderThread, at /home/dalley/Devel/servo-dev/media/audio/param.rs:335)

[Manishearth]

Can you paste the full backtrace?

[Manishearth]

Oh. Right.

media/audio/param.rs

Line 333 in 50ab227

unreachable!("CancelScheduledValues/SetValue should never appear in the timeline")

That should return the inner time. My bad.

[Manishearth]

But the others should still panic

[dralley]

How about now?

[Manishearth]

@bors-servo r+

Feel free to also add a test for this

[bors-servo]

📌 Commit eafa387 has been approved by Manishearth

[bors-servo]

⌛ Testing commit eafa387 with merge 783d5ba...

[dralley]

@Manishearth I have no idea how to add a test for this unfortunately, first Servo PR. I'd be willing to do so but I'd need some guidance

[Manishearth]

No biggie. If you want to try, you need to add another example under examples/ (make sure you add it to Cargo.toml. Perhaps copy one of the params examples and make it mess with cancel messages.

[bors-servo]

☀️ Test successful - checks-travis
Approved by: Manishearth
Pushing 783d5ba to master...