renseiai/donmai-kits/rust-debugging

Rust Debugging

Overview

Debugging Rust compile errors, borrow-checker failures, clippy lints, and test failures. Systematic diagnosis for the most common Cargo failure modes.

Triggers

Use this skill when:

• cargo build fails to compile (borrow checker, trait bounds, lifetimes)
• cargo clippy -- -D warnings blocks the validate gate
• cargo test fails, panics, or doctests break
• cargo fmt --check reports formatting drift

Debugging Workflow

1. Compile / Borrow-Checker Errors

cargo build 2>&1 | head -60

Read the FIRST error and its help: / note: lines — rustc's diagnostics usually point at the exact fix.

Common root causes:

• Borrow conflicts — restructure ownership, clone deliberately, or scope the

borrow with a block

• Lifetime mismatches — name the lifetime explicitly or return an owned value
• Missing trait bounds — add where T: Trait or derive the trait
• Moved value used after move — borrow (&) instead, or clone

2. Clippy Lints (validate gate)

cargo clippy -- -D warnings 2>&1 | head -40

Fix the lint rather than #[allow(...)]-ing it; clippy's suggestion is usually the idiomatic form.

3. Test Failures

cargo test 2>&1 | grep -E "FAILED|panicked|error\[" | head -30

Common root causes:

• unwrap()/expect() panics on None/Err — handle the variant
• Doctest failures — the example in /// comments must compile and run
• Integration tests in tests/ need the crate's public API only

Notes

• cargo/rustc live in ~/.cargo/bin. If a command reports cargo: not found,

source ~/.cargo/env first (the toolchain installer wrote it there).