When loading VS Code extension, show a warning if rust-lang.rust is also installed

[matklad]

[matklad]

See #6461

[lnicola]

Detecting installed extensions might be possible using https://code.visualstudio.com/api/references/vscode-api#extensions (it might be worth checking that the current extension is matklad.rust-analyzer, though). We could display a message suggesting the user to uninstall one of them.

[xFrednet]

Hey I was looking at this issue to figure out how difficult it would be to implement it. (For me as new comer).

I'm pretty sure that the suggested solution by @lnicola would work but it would be vscode specific from what I can see. Is there maybe a way to implement it with the pure LSP specification? (I couldn't find one). If it's not possible would it be worth to suggest such a feature for the LSP specification in addition to implementing it with the vs code specific way?

[lnicola]

Both extensions mentioned here are Code-specific (unless you count coc.nvim, but that one exposes the Code API and a fork of this extension), and there's no idea of an extension in LSP -- why would there be?

There are LSP clients that don't support extensions, and for those that do, there's no extension to be in conflict with. We could check that RLS is not running, but the referenced issues are in the official Code extension, not in the language servers.

[xFrednet]

Okay, it seems like I've misunderstood a part of the LSP. Thank you very much for clarifying!

[extremegf]

I've create a pull requests that adds this warning. I kindly request comments.

This is my first pull request for RA, so forgive me if I missed something.