rust-crate-ci

Rust Crate CI Guide

This repo contains a Rust crate at runners/swarm-sandbox-runner/. The CI job that validates it is rust-sandbox-runner (runs on windows-latest). This guide prevents the most common failure modes before they reach CI.

Mandatory local gate (run in order before pushing)

cd runners/swarm-sandbox-runner

# 1. Format check — CI fails here first; clippy will not run if this fails
cargo fmt --check

# 2. Clippy — -D warnings makes all warnings hard errors; --all-targets matches CI,
#    which also lints tests, examples, and benches (ci.yml rust-sandbox-runner job)
cargo clippy --all-targets -- -D warnings

# 3. Tests — --all-targets matches CI; Windows-specific tests are gated with #[cfg(windows)]
cargo test --all-targets

# 4. Release build — confirms the binary compiles with optimizations
cargo build --release

Run them in this exact order. If cargo fmt --check fails, fix formatting first — clippy errors may be masked until fmt passes.

If cargo is not in PATH locally (e.g. you are on a machine without Rust installed), push to a draft PR and let CI run the checks. Read the CI log carefully; do not guess at what failed.

How rustfmt makes decisions

rustfmt (current stable — rust-toolchain.toml floats on channel = "stable") applies line-length thresholds per syntax item, not per file or per block. Two patterns that look equivalent locally can format differently:

Long format! macros: If the total length of format!("...", arg) exceeds the line limit, rustfmt splits it. If it fits on one line, rustfmt collapses it.

// rustfmt will COLLAPSE this to one line if it fits:
return Err(RunnerError::PolicyViolation {
    reason: format!(
        "cwd resolves outside allowed roots (symlink egress): {canonical_str}"
    ),
});

// rustfmt will SPLIT this if it exceeds the limit:
events::emit(&events::denial_event("deny_symlink_egress", Some(canonical_str)));
// becomes:
events::emit(&events::denial_event(
    "deny_symlink_egress",
    Some(canonical_str),
));