1780158 - Exclude JSOp::SetAliasedVar ".generator" from Debugger.Script.getEffectfulOffsets

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect, P1)

Description

[Tooru Fujisawa [:arai]]

The following code expects setBreakpoint doesn't throw, but bug 1776376 changed the behavior and now it can throw.

https://searchfox.org/mozilla-central/rev/f6a2ef2f028b8f1eb82fa5dc5cb1e39a3baa8feb/devtools/server/actors/webconsole/eval-with-debugger.js#377-380

const offsets = script.getEffectfulOffsets();
for (const offset of offsets) {
  script.setBreakpoint(offset, handler);
}

The issue here is the following:

• Bug 1776376 patch wants to hide the JSOp::SetAliasedVar ".generator" from consumer
• getEffectfulOffsets doesn't hide it because it thinks the instruction is effectful

Then, JSOp::SetAliasedVar ".generator" isn't actually "effectful" in term of getEffectfulOffsets method's definition.

https://searchfox.org/mozilla-central/rev/fa71140041c5401b80a11f099cc0cd0653295e2c/js/src/doc/Debugger/Debugger.Script.md#360-365

### `getEffectfulOffsets()`
**If the instance refers to a `JSScript`**, return an array
containing the offsets of all bytecodes in the script which can have direct
side effects that are visible outside the currently executing frame.  This
includes, for example, operations that set properties or elements on
objects, or that may set names in environments created outside the frame.

JSOp::SetAliasedVar ".generator" sets engine-internal variable, and it's not visible outside the frame.

We can change getEffectfulOffsets not to return the JSOp::SetAliasedVar ".generator", so that the above code in devtools keeps working.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1776376

Comment 2

[Tooru Fujisawa [:arai]]

Attachment: Bug 1780158 - Exclude JSOp::SetAliasedVar .generator from Debugger.Script.getEffectfulOffsets. r?mgaudet!

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug is a defect, but please change it back in case of error.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bbe1d96dc63d
Exclude JSOp::SetAliasedVar .generator from Debugger.Script.getEffectfulOffsets. r=mgaudet

Comment 5

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/bbe1d96dc63d