Code coverage is not collected from `Worker` context(s)

[canonic-epicure]

$ deno --version
deno 1.17.0 (release, x86_64-unknown-linux-gnu)
v8 9.7.106.15
typescript 4.5.2

It seems code coverage is not collected for scripts from the worker contexts (neither from the worker script itself, nor from the imported scripts).

Steps to reproduce:

1. Clone the git@github.com:canonic-epicure/deno-reproduce.git
2. Inside the repo folder, run DENO_UNSTABLE_COVERAGE_DIR=cov deno run -A --unstable reproduce.js
3. Search inside the cov folder, it contains a single file for every file, for which coverage information was collected.
   There should be a file containing the text: lib.js and worker.js, but there's none. The file for reproduce.js presents as expected.

[csunday95]

investigating this issue, and it seems web workers don't currently receive or create an inspector session for coverage collecting. Only the main worker creates one in the case where coverage_dir is supplied in the ProcessState. I'm not sure if the inspector session is meant to be shared between workers, or if one is required per worker. The comment on JsRuntimeInspector::create_local_session() states

  /// Create a local inspector session that can be used on
  /// the same thread as the isolate.

and mspc channels are used, so I assume there are some threading considerations.

[jespertheend]

Oops sorry, not sure how I missed that.

[kaffeeumeins]

I can confirm, with 2.1.1 the coverage is still not collected from work threads.
deno 2.1.1 (stable, release, aarch64-apple-darwin)
v8 13.0.245.12-rusty
typescript 5.6.2

[bartlomieju]

This should be possible to fix, immediately after #30743 lands. The fix won't be involved either.