Can't specify features for individual crates in a virtual workspace

[Michael-F-Bryan]

When you have a workspace containing multiple crates in subdirectories and those crates have their own feature flags, it's not possible to specify which feature flags to use when checking/navigating that project.

Setting rust-analyzer.cargo.features doesn't work because cargo errors with "error: --features is not allowed in the root of a virtual workspace", same as if I ran cargo check --features foo from the workspace root.

This becomes particularly evident if you are continuously recompiling and running tests in a background terminal (e.g. cd sub-crate && cargo watch -x "check --features foo"). Rust Analyzer ends up compiling the crate/workspace without the feature and cargo watch compiles with it. That means you'll constantly be rebuilding the entire crate... Which can be quite expensive when the feature flag enables several transitive dependencies (e.g. tokio and a HTTP server).

[matklad]

If you are running cargo watch anyway, you should set rust-analyzer.checkOnSave.enable: false. Cargo watch should still provide you with inline error markers, via the problem matcher.

[Michael-F-Bryan]

Cargo watch should still provide you with inline error markers, via the problem matcher

Does the problem matcher need cargo watch to be running inside a VS Code terminal? I run cargo watch completely separately from VS Code, and when I disabled checkOnSave and restarted VS Code it didn't show me any inline error messages.

[matklad]

You need to run it as a vscode task, the following definition should work

    {
      "label": "Watch",
      "group": "build",
      "type": "shell",
      "command": "cargo watch --package rust-analyzer",
      "problemMatcher": "$rustc-watch",
      "isBackground": true
    },

[jonas-schievink]

This is a Cargo limitation that will be addressed by rust-lang/rfcs#2957.

[matklad]

I belive this was fixed on the cargo side with the introduction of resolver=2