Discover unlinked projects and suggest adding them to the settings

[matklad]

In rust-analyzer, it's important to know the set of opened projects up-front. This set of project is stored in the linkedProjects config.

It is possible to link projects dynamically & lazily -- the first time you open an rs file, find the corresonding toml and add it to the project. This has surprising interaction with find usages: if A uses B, and you open B and run fiend usages (or some refactor based on fiend usages), then you'd see usages in A only if you happened to open A in this editing session as well. So, we really want to know, up front, that both A and B exist.

What we could do though, is to notice a project which isn't link, and show a dialog in the edditor asking the user to (automatically), add the newly disccovered project to settings.json.

This needs some work on the server (to notice unlinked projects) and on the client (to actually modilfy the settings).

[flodiebold]

Similar thing in pylance: https://devblogs.microsoft.com/python/python-in-visual-studio-code-july-2021-release/#a-faster-way-to-configure-project-roots

[liby]

I think it's a great idea. With it, many beginners like me won't have issues like #6605.

[ValarDragon]

This would be amazing, we define rust crates embedded within go packages for our projects, this would save us a lot of complexity in IDE setup