[wish] warn when lang-server version is old

[nahuel]

I found I was using a very old ts-ls version without knowing it, have had to delete .emacs.d/.cache/npm/typescript-language-server to force lsp-mode download the latest one. It will be nice if lsp-mode warned when connecting to a lang-server who is not the latest one (no need to reach the net, just using a hardcoded list of desired/latest versions). Using an old lang-server without knowing it seems like a potential big source of (maybe only apparent) bugs.

[yyoncho]

There is no generic way to do so which means that we should create a custom way to check whether each of the servers(70+) is the latest version. I am a bit sceptical that this will be addressed anytime soon. FTR you can use C-u M-x lsp-install-server to force update for a particular server.

[nahuel]

Since LSP 3.15.0 the server InitializeResult reply includes a server version string:

interface InitializeResult {
	/**
	 * The capabilities the language server provides.
	 */
	capabilities: ServerCapabilities;

	/**
	 * Information about the server.
	 *
	 * @since 3.15.0
	 */
	serverInfo?: {
		/**
		 * The name of the server as defined by the server.
		 */
		name: string;

		/**
		 * The server's version as defined by the server.
		 */
		version?: string;
	};
}

Taken from: https://microsoft.github.io/language-server-protocol/specifications/specification-current/#initialize

Can this version string be used for this purpose on a generalized way?

[yyoncho]

We can check the server version that runs locally, but we won't know if a newer version is available.

[nahuel]

Maybe lsp-mode can include a harcoded list of the latest known lang-servers versions (or the latest version known to be compatible and well tested with lsp-mode), so it not needs to make a network request to check if a new one is available. I think is a good compromise vs the actual situation of installing a lang-server once, forget about it and then be unknowingly stuck on an old version.

[yyoncho]

Ideally, we should do that - ship lsp-mode with a tested version of the server. Unfortunately, this would require a lot of maintenance work for all of the servers on our side.