This is a quick way to implement unresolved reference diagnostics.
For example, adding to VS Code config
"editor.tokenColorCustomizationsExperimental": {
"unresolvedReference": "#FF0000"
},
will highlight all unresolved refs in red.
rust-analyzer
Provides support for rust-analyzer: novel LSP server for the Rust programming language.
See https://rust-analyzer.github.io/ for more information.