`Microsoft.CodeAnalysis.LanguageServer` does not respect dynamic registration for diagnostics

[SofusA]

Version Used:
4.13.0-3.24629.5

Steps to Reproduce:

1. Start the language server
2. Send initialize message with pull diagnostics with dynamicRegistration: false:

{"jsonrpc":"2.0","method":"initialize","params":{"capabilities":{"general":{"positionEncodings":["utf-8","utf-32","utf-16"]},"textDocument":{"codeAction":{"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["","quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}},"dataSupport":true,"disabledSupport":true,"isPreferredSupport":true,"resolveSupport":{"properties":["edit","command"]}},"completion":{"completionItem":{"deprecatedSupport":true,"insertReplaceSupport":true,"resolveSupport":{"properties":["documentation","detail","additionalTextEdits"]},"snippetSupport":true,"tagSupport":{"valueSet":[1]}},"completionItemKind":{}},"diagnostic":{"dynamicRegistration":false,"relatedDocumentSupport":true},"formatting":{"dynamicRegistration":false},"hover":{"contentFormat":["markdown"]},"inlayHint":{"dynamicRegistration":false},"publishDiagnostics":{"tagSupport":{"valueSet":[1,2]},"versionSupport":true},"rename":{"dynamicRegistration":false,"honorsChangeAnnotations":false,"prepareSupport":true},"signatureHelp":{"signatureInformation":{"activeParameterSupport":true,"documentationFormat":["markdown"],"parameterInformation":{"labelOffsetSupport":true}}}},"window":{"workDoneProgress":true},"workspace":{"applyEdit":true,"configuration":true,"diagnostic":{"refreshSupport":true},"didChangeConfiguration":{"dynamicRegistration":false},"didChangeWatchedFiles":{"dynamicRegistration":true,"relativePatternSupport":false},"executeCommand":{"dynamicRegistration":false},"fileOperations":{"didRename":true,"willRename":true},"inlayHint":{"refreshSupport":false},"symbol":{"dynamicRegistration":false},"workspaceEdit":{"documentChanges":true,"failureHandling":"abort","normalizesLineEndings":false,"resourceOperations":["create","rename","delete"]},"workspaceFolders":true}},"clientInfo":{"name":"helix","version":"24.7 (74a9e9e4)"},"processId":125487,"rootPath":"/var/home/sofusa/TestProj","rootUri":"file:///var/home/sofusa/TestProj","workspaceFolders":[{"name":"TestProj","uri":"file:///var/home/sofusa/TestProj"}]},"id":0}

Expected Behavior:
Server responding with diagnostics being a server capability.

Actual Behavior:
It is not, but the server will still respond to pull diagnostics.

Motivation

I am using this language server with Helix editor.

Unfortunately this issue requires me to patch the server capabilities to trick my editor to send pull diagnostics requests.

I think that this is a requirement if Microsoft.CodeAnalysis.LanguageServer should be able to support other editors than Visual Studio Code.

Ps. Thanks for your work. I can actually use this with Helix (with some hack) and it is rock solid!

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[dibarbet]

I see the issue - in pull diagnostics we make heavy use of diagnostic sources, but static registration only allows you to register a single diagnostic source.

If the client does not support dynamic registration, we should probably fall back to statically registering diagnostics with no diagnostic source. This means the server will return all diagnostics from all sources in a single request. This is definitely slower and can lead to a worse experience especially if there is a poor performing analyzer, but I don't think we can do better if the client does not support dynamic registration.

[SofusA]

Thanks for addressing the issue.
I think this is a fine compromise. It would definitely be better than not supporting editors without dynamic registration.

[dibarbet]

I will not likely have time to get to this soon, but would be happy to take a contribution here. Roughly, the change would be adding a check for the client's diagnostic dynamic registration support here and setting the server capability if dynamic registration is not supported. Then adding a test here to verify when dynamic capabilities are not supported we get the correct server capability.