cargo Command: Build & Test Rust in CI

cargo builds, tests, and packages Rust crates and manages their dependencies.

cargo is the standard entry point for Rust CI: it resolves dependencies from crates.io, compiles via rustc, and runs tests. The build/test subcommands plus a handful of flags cover almost every pipeline step.

Common flags

cargo build - compile the package and its dependencies
cargo test - build and run unit, integration, and doc tests
--release - optimized build (slower compile, faster binary)
--locked - fail if Cargo.lock is out of date (deterministic CI)
--all-features / --no-default-features - control feature flags
--workspace - operate on all members of the workspace
--target-dir DIR - relocate build output (handy for caching)

Example in CI

A reproducible release build and test pass with locked dependencies:

shell

cargo build --release --locked
cargo test --workspace --all-features --locked

Common errors in CI

error: the lock file Cargo.lock needs to be updated but --locked was passed
error: failed to select a version for X - incompatible version constraints
error: no matching package named X found - wrong name or missing registry
error: failed to run custom build command for openssl-sys - missing system libs

Key takeaways

Use --locked in CI so builds are reproducible and lockfile drift fails fast.
cargo test also runs doc tests; --all-features widens coverage.
Cache the target dir and ~/.cargo to cut compile time on managed runners.