1457197 - Lazy parsing is disabled when Code Coverage is enabled.

Status: NEW

(Core :: JavaScript Engine, enhancement, P3)

Description

[Nicolas B. Pierron [:nbp] {away}]

This bug causes false-negative coverage reports, by preventing the lazy-parser to be detected when the code coverage of JavaScript is enabled in the JavaScript engine.

The reason the lazy parsing is disabled [1] is to avoid getting multiple reports from a script which is being executed, relazified and re-executed.

We can solve this issue by removing the indexing based on the JSScript, held in the compartment, and moving towards an indexing based on the ScriptSource / ScriptSourceObject in addition to the sourceStart_ & sourceEnd_ instead of the JSScript.

[1] https://searchfox.org/mozilla-central/rev/78dbe34925f04975f16cb9a5d4938be714d41897/js/src/frontend/BytecodeCompiler.cpp#211

Comment 1

[Matthew Gaudet (he/him) [:mgaudet]]

Seems like maybe this restriction no longer exists: https://searchfox.org/mozilla-central/source/js/src/frontend/BytecodeCompiler.h#283-286

Nicolas, am I correct here?

Comment 2

[Nicolas B. Pierron [:nbp] {away}]

This is still the case as of today:
https://searchfox.org/mozilla-central/rev/0b1d02b2cb5736511139cf0e40b318273e825899/js/src/shell/js.cpp#12755-12758