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name: rust description: Use when developing Rust projects in the tempoxyz org—standardizes fmt/clippy/nextest, sccache+mold, feature-powerset checks, MSRV builds, docsrs flags, and xtask patterns so local and CI behavior match.

Rust (tempoxyz conventions)

Overview

Fast, reproducible Rust workflows aligned with tempoxyz repos: cached toolchains, mold + sccache, clippy-as-error, nextest, feature-matrix checks, docsrs parity, and xtask utilities.

Doc-first, no guessing: Always consult official docs (rust-lang.org/edition-guide, doc.rust-lang.org/std, crate docs on docs.rs). If the exact flag/API/version isn’t in docs or you’re unsure, pause and ask for the correct link instead of inferring.

When to Use

• Working on Rust crates (tempo, reth-commonware, tempo-commonware, dex-kv, tempo-std, etc.).
• Adding CI steps or local scripts to match repo expectations.
• Verifying docs/build across MSRV and nightly.

Core Pattern

1. Toolchain + components

   • Default: stable; lint: nightly with clippy / rustfmt when required.
   • MSRV guard: pin (e.g., toolchain: "1.88") and run cargo build --bin <name>.

2. Standard commands (keep consistent with CI)

   • Setup tools: install toolchains, sccache, mold, nextest, cargo-hack, typos, deny.
   • Format: cargo fmt --all --check.
   • Lint: cargo clippy --all-targets --all-features --locked -- -D warnings.
   • Test: cargo nextest run --no-fail-fast -j num-cpus.
   • Features: cargo hack check --feature-powerset --depth 1.
   • Docs: cargo doc --workspace --all-features --no-deps with docsrs flags.
   • MSRV: pinned-toolchain build (e.g., cargo +1.88 build --bin <name>).

3. Performance

   • Use mold linker (rui314/setup-mold@v1 or -Zshare-generics not needed).
   • Enable sccache (mozilla-actions/sccache-action@v0.0.9); set RUSTC_WRAPPER=sccache.

4. Checks

   • Format: cargo fmt --all --check.
   • Lint: cargo clippy --all-targets --all-features --locked -- -D warnings.
   • Tests: cargo nextest run --no-fail-fast -j num-cpus (install via taiki-e/install-action@nextest).
   • Feature surface: cargo hack check --feature-powerset --depth 1 for broad combos.
   • Licenses/Deps: cargo deny check (reuse workflow), cargo vet if present.
   • Typos: typos (crate-ci/typos@v1).
   • Custom sanity: zepter run check (from tempo).

5. Docs parity

   • cargo doc --workspace --all-features --no-deps --document-private-items.
   • RUSTDOCFLAGS: --cfg docsrs -D warnings --show-type-layout --generate-link-to-definition --enable-index-page -Zunstable-options.

6. Xtask utilities

   • Use existing cargo xtask commands (e.g., cargo xtask generate-genesis ...) instead of ad-hoc scripts.
   • Keep generated artifacts compared into repo fixtures (diff & fail if drift).

7. Env defaults

   • CARGO_TERM_COLOR=always, RUST_BACKTRACE=full, RUSTFLAGS="-D warnings" for builds where appropriate.

8. Caching

   • Combine sccache with Swatinem/rust-cache@v2 in CI; keep lockfiles pinned.

Quick Reference

Task	Command
Format	cargo fmt --all --check
Lint	cargo clippy --all-targets --all-features --locked -- -D warnings
Test	cargo nextest run --no-fail-fast -j num-cpus
Feature sweep	cargo hack check --feature-powerset --depth 1
Docs	cargo doc --workspace --all-features --no-deps (+ docsrs flags)
MSRV	cargo build --bin tempo with pinned toolchain
Typos	typos
Zepter	zepter run check

Common Mistakes

• Running cargo test without nextest → slower/less parallel.
• Skipping --locked causing feature drift.
• Forgetting mold/sccache → slow CI.
• Leaving RUSTFLAGS unset → warnings slip through.
• Not updating docs when public API changes; docs job will fail in CI.
• Missing Justfile or targets drift from CI steps → contributors can’t run parity commands locally.

Red Flags

• No clippy -D warnings.
• Feature-powerset not checked in multi-feature crates.
• MSRV not validated when adding new dependencies.
• Generated fixtures updated manually instead of via xtask.
• Docsrs flags missing; doc build passes locally but fails on docs.rs.

Verification

• cargo fmt && cargo clippy ... && cargo nextest ... passes locally with sccache/mold configured.
• cargo hack check --feature-powerset --depth 1 passes or is consciously scoped.
• MSRV build succeeds on pinned toolchain.
• Docs build with docsrs flags succeeds.

Rationalizations Countered

Excuse	Counter
"Nextest is optional"	It’s the default in CI and faster; keeps parity.
"mold/sccache not worth it"	Significant speedups; trivial to add.
"Warnings are fine"	CI treats warnings as errors; fix locally first.
"Feature matrix is too big"	cargo hack --depth 1 limits blast radius while catching combos.