{"slug":"ia-rust-systems","title":"ia-rust-systems","summary":"Rust patterns for CLI tools, backend services, and general application code. Use when working with Rust, Cargo workspaces, axum/tokio services, clap CLIs, async concurrency, or configuring clippy, rustfmt, cargo-nextest, or Cargo.toml.","platform":"Claude","tags":[],"authorName":"LLM Mart","authorSlug":"llm-mart","score":0,"source":"github","price":null,"verified":false,"createdAt":"2026-09-08T18:29:50.534262Z","repo":{"url":"https://github.com/iliaal/whetstone","stars":35,"forks":4,"license":"MIT","updatedAt":"2026-09-24T18:37:09Z"},"bodyHtml":"<hr>\n<h2>name: ia-rust-systems\nclass: language\ndescription: &gt;-\nRust patterns for CLI tools, backend services, and general application code.\nUse when working with Rust, Cargo workspaces, axum/tokio services, clap CLIs,\nasync concurrency, or configuring clippy, rustfmt, cargo-nextest, or Cargo.toml.\npaths: \"<strong>/*.rs,</strong>/Cargo.toml\"</h2>\n<h1>Rust Systems &amp; Services</h1>\n<p>Covers modern application-layer Rust (edition 2024): CLIs, web services, libraries. Not <code>no_std</code>/embedded.</p>\n<h2>Working rules</h2>\n<ul>\n<li>Preserve error variants in libraries and add operational context at application boundaries.</li>\n<li>Distinguish missing configuration from unreadable or invalid files before writing replacements.</li>\n<li>Keep blocking work off async workers, bound queues and spawned work, and define shutdown behavior.</li>\n<li>Trace exported interfaces before treating a change as internal; verify installed runtime capabilities.</li>\n<li>Do not mutate process-wide state in concurrent tests; exercise the real binary and relevant feature combinations.</li>\n</ul>\n<h2>Unsafe Discipline</h2>\n<ul>\n<li>Default: no <code>unsafe</code>. If clippy flags it, don't <code>#[allow]</code> it — refactor. The <code>#[expect]</code> escape hatch below does not apply here; unsafe findings get fixed, not annotated.</li>\n<li>Every <code>unsafe</code> block gets a <code>// SAFETY:</code> comment above it explaining why each invariant holds. No comment = reviewer rejects.</li>\n<li>Keep <code>unsafe</code> blocks minimal — wrap in a safe abstraction at module boundary, mark the module <code>pub(crate)</code>.</li>\n<li>Use <code>miri</code> (<code>cargo +nightly miri test</code>) on any crate containing <code>unsafe</code> or raw pointer arithmetic — catches UB that optimizers mask.</li>\n<li>Prefer <code>bytemuck</code>, <code>zerocopy</code>, <code>bytes</code> over hand-rolled transmutes for zero-copy patterns.</li>\n<li><strong>Env-var writes are <code>unsafe</code> in edition 2024. Write them only in <code>main</code>, before the runtime starts or any thread spawns.</strong> Concurrent <code>getenv</code> is UB; <code>OnceLock</code> does not make it safe. Watch for lazy <code>LD_LIBRARY_PATH</code>-style writes on first use — hoist them to startup.</li>\n</ul>\n<h2>Discipline</h2>\n<ul>\n<li>Simplicity first — every change as simple as possible, impact minimal code.</li>\n<li>Only touch what's necessary — avoid unrelated changes in a PR.</li>\n<li>No <code>#[allow(clippy::...)]</code> as a shortcut — fix the underlying issue. When a suppression is genuinely warranted, write <code>#[expect(clippy::lint_name, reason = \"...\")]</code> instead: <code>expect</code> warns once the lint stops firing, so a suppression that has outlived its cause reports itself, where <code>allow</code> rots silently forever. (<code>expect</code> needs Rust 1.81+; edition 2024 clears that floor.)</li>\n<li>Before adding a trait or generic, verify it's used in 3+ places. Otherwise a concrete type is clearer.</li>\n<li><strong><code>bool::then_some(x)</code> takes <code>x</code> by value — the argument is computed before the bool is consulted</strong>, so a guard written as a condition plus a fixed-width slice panics on exactly the inputs the condition was checking for: <code>(b.len() &gt;= 19 &amp;&amp; b[4] == b'-').then_some(&amp;v[..19])</code> panics on any shorter value, exiting 101 inside the one function written to report the case as undetermined. Use <code>then(|| …)</code>, which is lazy. Clippy does not flag the difference. Grep <code>then_some(</code> for an argument that indexes, slices, unwraps, or allocates. Related: <strong>a fixed-width slice is not a parse</strong> — <code>&amp;v[..19]</code> also panics mid-character on non-ASCII, and comparing two such prefixes lexicographically drops the timezone offset, so <code>01:00+02:00</code> sorts after <code>00:00Z</code> while being an hour earlier. Parse and normalize, or reject.</li>\n</ul>\n<h2>Verify</h2>\n<ul>\n<li><code>cargo fmt --all -- --check</code> passes with zero diffs</li>\n<li><code>cargo clippy --workspace --all-targets --all-features -- -D warnings</code> passes</li>\n<li><code>cargo nextest run --workspace</code> (or <code>cargo test --workspace</code>) passes with zero failures</li>\n<li><code>cargo deny check</code> passes (licenses, advisories, duplicates) for any crate going to production</li>\n<li>No new <code>unsafe</code> without <code>// SAFETY:</code> comment</li>\n</ul>\n<h2>Task-specific references</h2>\n<p>Read the relevant reference before implementing or reviewing the matching behavior:</p>\n<ul>\n<li>For Cargo setup, workspace changes, public API reachability, build profiles, or CI: <a href=\"./references/toolchain-and-interfaces.md\">toolchain-and-interfaces.md</a>.</li>\n<li>For errors, ownership, parsing boundaries, Tokio, shutdown, or concurrency: <a href=\"./references/ownership-and-execution.md\">ownership-and-execution.md</a>.</li>\n<li>For CLI/service entrypoints, production resilience, telemetry, or tests: <a href=\"./references/applications-and-testing.md\">applications-and-testing.md</a>.</li>\n</ul>\n<p>Existing specialized references, when the corresponding topic applies:</p>\n<ul>\n<li><a href=\"./references/macros-and-os-boundaries.md\">macros-and-os-boundaries.md</a>.</li>\n<li><a href=\"./references/rustdoc.md\">rustdoc.md</a>.</li>\n<li><a href=\"./references/build-profiles.md\">build-profiles.md</a>.</li>\n<li><a href=\"./references/performance.md\">performance.md</a>.</li>\n<li><a href=\"./references/cli-tools.md\">cli-tools.md</a>.</li>\n<li><a href=\"./references/production-resilience.md\">production-resilience.md</a>.</li>\n<li><a href=\"./references/axum-service.md\">axum-service.md</a>.</li>\n<li><a href=\"./references/observability.md\">observability.md</a>.</li>\n<li><a href=\"./references/ci-pipeline.md\">ci-pipeline.md</a>.</li>\n</ul>\n","files":[{"path":"references/applications-and-testing.md","sizeBytes":4978,"isText":true},{"path":"references/axum-service.md","sizeBytes":9004,"isText":true},{"path":"references/build-profiles.md","sizeBytes":1793,"isText":true},{"path":"references/ci-pipeline.md","sizeBytes":1464,"isText":true},{"path":"references/cli-tools.md","sizeBytes":6647,"isText":true},{"path":"references/macros-and-os-boundaries.md","sizeBytes":4017,"isText":true},{"path":"references/observability.md","sizeBytes":2629,"isText":true},{"path":"references/ownership-and-execution.md","sizeBytes":7909,"isText":true},{"path":"references/performance.md","sizeBytes":1518,"isText":true},{"path":"references/production-resilience.md","sizeBytes":2991,"isText":true},{"path":"references/rustdoc.md","sizeBytes":2562,"isText":true},{"path":"references/toolchain-and-interfaces.md","sizeBytes":5330,"isText":true},{"path":"SKILL.md","sizeBytes":4901,"isText":true},{"path":"SPEC.md","sizeBytes":4441,"isText":true}],"reviewScore":null,"reviewSummary":null,"trust":{"provenance":"trusted-source-unreviewed","notice":"Community-authored content, reproduced verbatim and not vetted as instructions. 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