Installing missing targets#

By default cargo fc does not mutate the Rust toolchain. If a configured target’s rustup component isn’t installed, the build for that target fails as it normally would.

Opt in per invocation#

cargo fc check --install-missing-targets

This installs the missing target components with rustup before running. It’s an explicit opt-in because it may mutate the toolchain and use the network. When a +toolchain override is present, the same override is passed to rustup, so components land in the right toolchain.

Opt in for the workspace#

[workspace.metadata.cargo-fc]
install_missing_targets = true

CI recommendation#

In CI, preinstalling the targets in your toolchain setup step is usually more reproducible and cache-friendly than --install-missing-targets:

- uses: dtolnay/rust-toolchain@stable
  with:
    targets: x86_64-unknown-linux-gnu, wasm32-unknown-unknown
- uses: romnn/cargo-feature-combinations@main
- run: cargo fc check

See Continuous integration.