rust-programming

name: rust-programming description: Rust development guidance for creating, modifying, reviewing, testing, packaging, and debugging Rust crates, CLIs, services, and libraries. Use when tasks involve .rs files, Cargo.toml, Cargo.lock, workspaces, ownership, lifetimes, traits, async Rust, tokio, serde, cargo fmt, cargo test, cargo clippy, or Rust dependency management.

Rust Programming

Goal

Make Rust changes that are explicit about ownership, error paths, feature flags, and public API compatibility.

Discovery

• Read Cargo.toml, Cargo.lock, workspace config, feature flags, examples, benches, and CI before editing.
• Inspect nearby modules and tests to understand error types, trait style, visibility, async runtime, and serialization conventions.
• Preserve crate boundaries and public API stability unless the user asks for a breaking change.

Implementation

• Prefer clear ownership and borrowing over cloning; clone deliberately when it simplifies the API or avoids invalid lifetimes.
• Use Result and the crate's existing error approach (thiserror, anyhow, custom enums, or plain errors).
• Keep unsafe out of changes unless the project already requires it and the invariants are documented.
• Respect feature flags, no_std, platform-specific code, and workspace member boundaries.
• For async code, preserve the existing runtime and avoid blocking work on async executors.
• Keep trait bounds readable and introduce traits only when they reduce real coupling.

Verification

• Run cargo fmt on changed Rust code.
• Run targeted cargo test -p <crate> or cargo test <test-name> first, then broader workspace tests when shared code changed.
• Use cargo check for fast validation and cargo clippy when configured or useful for the change.

Review Focus

• Lifetime workarounds that hide ownership problems, accidental clones in hot paths, panics in library code, public API breaks, feature-gate regressions, async blocking, and lockfile changes unrelated to dependency edits.