Why building a Rust LSP is hard
This will be a (hopefully coherent) story about how Rust LSPs work, from the perspective of both rust-analyzer and Rust Glancer: how things that seem easy turn out to be hard, things that seem hard turn out to be even harder, and things I didn't expect to exist at all somehow do.
LSP is more of a guess game, where at each step all you are presented with is the potentially incorrect state, and your goal is to guess what would make sense for the user.