Filter package-scoped features

[mkeeter]

When rust-analyzer runs a flycheck on a binary package after a file write, it uses check -p regardless of rust-analyzer.check.workspace. This interacts poorly with package-specific features (in package/feature form) enabled in rust-analyzer.cargo.features.

Consider a workspace with two binary crates, foo and bar, each with a non-default feature:

[package]
name = "foo"
version = "0.1.0"
edition = "2024"

[features]
omg = []

[package]
name = "bar"
version = "0.1.0"
edition = "2024"

[features]
lol = []

I would like to enable both features, so I have configured rust-analyzer as such:

rust-analyzer.cargo.features = ["foo/omg", "bar/lol"]

The initial indexing and check work fine, because they happen in the workspace scope, and all of those features exist.

However, if I edit and save a file within one of the crates, the subsequent check happens with a package scope. This fails because all of the features are still passed to cargo check, but it's only targeting a single package:

2026-05-22T20:17:40.648309-04:00 ERROR Flycheck failed to run the following command:
CommandHandle {
  program: "/Users/mjk/.cargo/bin/cargo",
  arguments: [
    "check", "-p", "bar", "--bin", "bar", "--message-format=json",
    "--manifest-path", "/Users/mjk/code/r-a-test/Cargo.toml",
    "--keep-going", "--features", "foo/omg bar/lol"
  ],
  current_dir: Some("/Users/mjk/code/r-a-test")
},
error=Cargo watcher failed, the command produced no valid metadata (exit code: ExitStatus(unix_wait_status(25856))):
error: the package 'bar' does not contain this feature: foo/omg

(Repro repo is at mkeeter/ra-crate-features)

---

This PR adjusts CargoOptions::apply_on_command to take an optional package name. When the package name is present, package-specific features (package/feat) that do not match aren't passed to the cargo subcommand. Unscoped features (feat) are unmodified.

I believe this is a strict improvement to the previous behavior: passing package-specific features for packages not being built would always fail, and this PR eliminates those failure modes. It doesn't fix everything: unscoped features in rust-analyzer.cargo.features may still lead to failures, but that's a preexisting condition.

(This took a few false starts; apologies for the noise in #22421 and #22422)

[ChayimFriedman2]

I believe we have an issue about this.

Thanks!

View changes since this review

[mkeeter]

It looks like #10298 is the relevant issue!