If the user doesn't have rustc on $PATH, rust-analyzer won't be able to run `rustc --print cfg`. This isn't really an error, as rust-analyzer can still proceed without it. This is particularly noticeable when loading crates defined in a rust-project.json. Until the configuration is loaded, the opened files are briefly treated as detached files and users see this error. Environments with rust-project.json generally have a sysroot and rustc elsewhere, so the error confuses users.