Add boilerplate for pull-model diagnostics

[tristanlabelle]

Adds the capabilities, options and registration structs for pull-model diagnostics. I kept SwiftLanguageServer.initializeSync not reporting support for pull request diagnostics yet, so change currently has no impact.

Related to #500

How tested

• Locally added the snippet to report support for pull request diagnostics in SwiftLanguageServer.initializeSync, then built, ran locally in VS Code and confirmed that I could get a dummy diagnostic shown in VS Code.
• Then removed the feature reporting snippet (the state of the code in this PR), rebuilt, reran in VS Code, and confirmed that publishDiagnostics still work.

(sourcekit-lsp tests currently don't build on Windows and I don't have a mac machine handy)

[tristanlabelle]

@ahoppen You mentioned that support for pull diagnostic requests already exists in sourcekit. Any pointers on how to get to that data from the dummy SwiftLanguageServer.documentDiagnostic function?

[ahoppen]

LGTM. I really wonder how I missed all of this when updating the definitions to LSP 3.17 🤔

[ahoppen]

I think you also need to encode documentSelector (from TextDocumentRegistrationOptions in the LSP spec) and id (from StaticRegistrationOptions in the LSP spec) here.

[tristanlabelle]

Oops, I couldn't get to this before the PR got merged. I will address it in my next PR when implementing the feature.

[tristanlabelle]

documentSelector is already added to the dict by textDocumentRegistrationOptions.encodeIntoLSPAny(dict: &dict) at least.

[ahoppen]

Whoops, and I apparently approved and merged the PR, forgotting that I still had a comment. If you could create a follow-up PR, that would be great.

[ahoppen]

@swift-ci Please test

[ahoppen]

The main entry point where the diagnostic request is being handled in sourcekitd is here:

https://github.com/apple/swift/blob/0bdb39f51e54e959c44f3c0fea377d7d64155a51/tools/SourceKit/tools/sourcekitd/lib/Service/Requests.cpp#L1783-L1805

https://github.com/apple/swift/blob/main/test/SourceKit/Diagnostics/diags.swift has some examples of how the diagnostics request can be invoked using sourcekitd-test. You can see the raw sourcekitd request by running the test using lit with the -a option, which will print the output. In case you don’t want to do this yourself, this is what it produces for me.

{
  key.request: source.request.diagnostics,
  key.compilerargs: [
    "-module-cache-path",
    "/Users/alex/src/mbuild/Release+Asserts/swift-macosx-arm64/swift-test-results/arm64-apple-macosx10.13/clang-module-cache",
    "/Users/alex/src/swift/test/SourceKit/Diagnostics/diags.swift"
  ],
  key.sourcefile: "/Users/alex/src/swift/test/SourceKit/Diagnostics/diags.swift",
  key.primary_file: "/Users/alex/src/swift/test/SourceKit/Diagnostics/diags.swift"
}

And an example of how to send a request to sourcekitd can be found here:

https://github.com/apple/sourcekit-lsp/blob/e84b7b2b83ad4368926ca59a97c5c7484789267e/Sources/SourceKitLSP/Swift/CursorInfo.swift#L91-L106

I hope this gives you enough pointers to get started. Let me know if you need more help.