[LSP] Semantic tokens: Document null when first opening a Razor file

[allisonchou]

When a Razor file is opened, Roslyn at first is unable to find the Razor document, i.e. context.Document is null. However, the problem eventually resolves itself after a period of time. We should determine the core issue and implement a long-term solution.

[dibarbet]

@allisonchou I just hit this issue (in SemanticTokensHandler({"Document is null. - line 49"}) and I happened to be under the debugger. I found out that that the request context's solution does have the document that the request URI is for. However, it appears as though the document properties service is null, this line

roslyn/src/Features/LanguageServer/Protocol/Extensions/Extensions.cs

Line 67 in 2c03a46

var documentPropertiesService = document.Services.GetService<DocumentPropertiesService>();

In the following screenshot you can see that the documentPropertiesService is null, and in the immediate window the difference in querying the solution with and without the client name.

As a result, the handler throws because that method found no document with a matching client name.

[allisonchou]

@dibarbet have you seen this one recently? I haven't seen it in a while so I'm wondering if it might be resolved now.