Do not crash server if we fail to determine language for non-mutating request

[dibarbet]

Resolves dotnet/vscode-csharp#7656

Sometimes VSCode will send a request or two with the old URI after it renames a temporary file. When we close the file we lose the languageId that they told us about in didOpen (we drop the file info for it) and the server crashes.

Since this is a recoverable error, we should avoid crashing. Instead, we just fail the request and allow the server to continue running, unless it is a mutating request.

[CyrusNajmabadi]

do we want to report this somehow? it would be nice if we could push on this to get fixed at some point.

[CyrusNajmabadi]

catching naked exception feels... bad.

[CyrusNajmabadi]

i'd like us to be a little more careful/precise in exception handling.

[CyrusNajmabadi]

Since this is a recoverable error

Agreed, this is recoverable. From an impl perspective though, i'd prefer we check explicitly for this, and then fail gracefully vs throwing exceptions and catching all exceptions.

[dibarbet]

Agreed, this is recoverable. From an impl perspective though, i'd prefer we check explicitly for this, and then fail gracefully vs throwing exceptions and catching all exceptions.

I can do this to have the langue provider return if it could find it (instead of throwing internally). However I will still need to create an exception to serialize down to the client so it can observe the failure. But I can do that inside the queue handling if you'd prefer.

[CyrusNajmabadi]

But I can do that inside the queue handling if you'd prefer.

Yes please.