Child sessions that finish launching after their parent exits can break the debug UI

[connor4312]

See microsoft/vscode-js-debug#390 (comment): You should be able to reproduce by following the verification instructions with a js-debug-nightly version <= 2020.3.2517

[isidorn]

I see you were deep debugging into this. Do you have a proposed solution? How should the VS Code UI behave?

[connor4312]

Perhaps two things:

• Double check the parent session after returning from initialize (maybe launchAndAttach to?). Iff it's present and in State.Inactive, then terminate it and reject the request with a 'canceled' error

vscode/src/vs/workbench/contrib/debug/browser/debugService.ts

Line 531 in 2d85caa

await session.initialize(dbgr!);

• For the specific problem, it's probably safe to ignoreErrors in .expand. I see we do this elsewhere in the file. The set is cleared after that function runs, so ignoring problems here shouldn't have negative effects on state elsewhere.

vscode/src/vs/workbench/contrib/debug/browser/callStackView.ts

Line 136 in 52df596

this.parentSessionToExpand.forEach(s => this.tree.expand(s));

[isidorn]

These two are great proposals. I can look into them, thus assigning to March.
If you want a PR is also welcome, if not I will tackle on Monday.