tell server to support `textDocument/diagnostic`

[Sysix]

Background

As a server, I want to support all possible clients. Some will support textDocument/publishDiagnostics, some will textDocument/diagnostic. And some will support both.
I do not want to prepare a textDocument/publishDiagnostics object when the client can support textDocument/diagnostic.

To minimize the communication between server and client, the server wants to know if the client supports pull diagnostics.

Problem 1

The server is currently implemented in this way:
-> is sending to the server, <- is sending from the server.

-> initialize
-> initialized
-> textDocument/didOpen
<- textDocument/publishDiagnostics

When telling client (found it in VSCode) that we have some ClientCapabilities.DiagnosticProvider. The flow looks like this:

-> initialize
-> initialized
-> textDocument/didOpen
<- textDocument/publishDiagnostics
-> textDocument/diagnostic

I found no way to detect if the client supports textDocument/diagnostic before sending textDocument/publishDiagnostics.
Sending 2 times the same diagnostics is an overhead in my mind.

Problem 2

Probably an own issue, but this is related a bit.
The server does not need to support the new way textDocument/diagnostic. It wants to support workspace/diagnostic. Setting ClientCapabilities.DiagnosticProvider to tell the client that the server support workspace/diagnostic, will automatically enable textDocument/diagnostic

[rcjsuen]

I found no way to detect if the client supports textDocument/diagnostic before sending textDocument/publishDiagnostics

You should be able to use the client's capability and check for diagnostic.

/**
 * Text document specific client capabilities.
 */
export interface TextDocumentClientCapabilities {
	/**
	 * Capabilities specific to the diagnostic pull model.
	 *
	 * @since 3.17.0
	 */
	diagnostic?: DiagnosticClientCapabilities;
}

In the case of Visual Studio Code, you should get something like this in the initialize request.

{
    "capabilities": {
        "textDocument": {
            "diagnostic": {
                "dynamicRegistration": true,
                "relatedDocumentSupport": false
            }
        }
    }
}

[Sysix]

Thanks!