razor/mapToDocumentRanges hangs when called via Roslyn.CodeActionResolve -> CSharpSpanMappingService

[TanayParikh]

Extension of https://github.com/dotnet/aspnetcore/issues/27825.

So that https://github.com/dotnet/roslyn/pull/49592 can be reverted.

Occurs when a code action is attempted to be resolved. Ex.

@Debugger.Launch()

you select the lightbulb and hover over @using System.Diagnostics you get a spinning circle instead of the preview.

Issue is related to Razor calling textDocument/codeActionResolve to Roslyn, and then Roslyn calling for CSharpSpanMappingService.MapSpansAsync which in turn calls for razor/mapToDocumentRanges. This razor/mapToDocumentRanges request is what's hanging.

• [x] Check Telemetry Monitor
  • No $/cancelRequest while the code action resolve is showing the spinning circle. You do get a cancel request after you exit the code action resolve menu, but that's expected.
• [x] Check exceptions with Just My Code Disabled
  • Nothing related
• [x] Verify no hung threads via break-all
  • Didn't notice any deadlocks. I did see one thread in the default foreground scheduler but I think that's probably expected.
• [ ] ...

[TanayParikh]

This issue requires further investigation, I haven't had luck and I believe it may benefit from a fresh pair of eyes if someone has the bandwidth. I can go over what I've tried and how to setup the repro env offline.

[TanayParikh]

Needs another eye on this.