Rust Programmer

Goal: produce idiomatic, safe, and testable Rust with a repeatable verification loop.

Workflow

1) Clarify requirements

• Confirm crate type: library vs binary.
• Confirm runtime: sync vs async (Tokio or not).
• Confirm MSRV/toolchain constraints and target platforms.
• Confirm error strategy (public error type vs opaque errors).
• Identify public API surface and backwards-compat expectations.

2) Inspect the existing crate/workspace

• Read Cargo.toml (features, workspace members, lints, edition).
• Follow the current patterns (error types, logging/tracing, async runtime).
• Locate critical paths via rg and call sites (avoid introducing a new style).

3) Design before coding

• Use strongly typed data; avoid “stringly typed” APIs.
• Prefer ownership at boundaries and borrowing internally.
• Pick an error model:
  • Library: thiserror + a stable error enum.
  • Binary/CLI: anyhow + Context at boundaries.
• If async: avoid blocking calls in async contexts; use spawn_blocking for CPU/IO-bound sync work.

4) TDD (required for behavior changes)

• Add deterministic unit tests for pure logic.
• Add integration tests for public API and IO boundaries.
• Avoid timing-dependent tests unless required; keep retries bounded and explicit.

5) Implement (idiomatic + minimal diff)

• Prefer iterators, pattern matching, and small focused functions.
• Avoid unwrap/expect outside tests unless the invariant is proven and documented.
• Avoid unsafe unless necessary; document invariants and add coverage.

6) Verify

Run the standard checks (fast → slow):

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings (or match repo policy)
• cargo test --all --all-features

If useful, run the bundled script: scripts/cargo_verify.sh.

Output expectations

• State assumptions (toolchain, crate type, runtime).
• Summarize what changed and why.
• List verification (commands, tests).
• Call out compatibility risk if public APIs or features change.

Resources

• scripts/cargo_verify.sh: standard local verification runner.
• references/rust-playbook.md: deeper patterns and decision notes.