rust-checks

name	rust-checks
description	Validate a Rust change in sempkg cheaply — the right cargo command, the right feature flags, the shared target dir, and what to leave to CI. Use this skill BEFORE running any cargo command (build, test, clippy, check, run) in this repository, and when deciding whether a change is ready to hand to review.

sempkg Rust checks

Compiling this workspace is expensive (Lance + DataFusion + Arrow + llama-cpp). Two disk emergencies have already come from agents compiling carelessly. This skill is the cheap path. See CLAUDE.md's "Build & test policy" for the full rationale — this is the day-to-day cheat sheet version.

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First: are you allowed to compile at all?

If you are reviewing a PR — no. Read the diff and read CI:

gh pr checks <pr>
gh run view <run-id> --log-failed

CI runs three platforms, the real feature combinations and the functional MCP suite. A green local run on one machine tells you less than that. A red or missing CI run is the worker's defect to fix — hand it back as a finding.

If you are a worker — yes, and it is your job. The reviewer is not your test run. Everything below is for you.

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The feature flags (not optional)

sempkg cannot build with --all-features — it enables cuda, vulkan, rocm and metal at once, each needing a different vendor SDK. It will fail, and it will fail slowly.

# sempkg — always these two features, never --all-features
cargo clippy -p sempkg --features reranker,embeddings -- -D warnings
cargo test  -p sempkg --features reranker,embeddings

# sembundle — --all-features is fine here (no optional GPU backends)
cargo clippy -p sembundle --all-features -- -D warnings
cargo test  -p sembundle --all-features

CI's lint job runs with -D warnings, so a warning is a failure. Check it before you push, not after.

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Pick the cheapest command that proves your point

Goal	Command
Does it type-check?	cargo check -p <crate>
Did I break the crate I touched?	cargo test -p <crate>
Is it lint-clean?	cargo clippy -p <crate> <features> -- -D warnings
Is it formatted?	cargo fmt --all --check
Does it work on 3 OSes / all features?	CI. Do not do this locally.

Scope by crate (-p sempkg or -p sembundle — the two Rust workspace members). cargo test --workspace rebuilds everything and is almost never what you actually need.

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The target dir is shared — it is not yours

All agents in a working group share one CARGO_TARGET_DIR (.loomux-target/, gitignored). That sharing is the only reason N worktrees don't each pay for a cold build.

• Never set your own CARGO_TARGET_DIR.
• Never build into your scratchpad or create a target-<name>/ directory. That is a from-scratch build of the whole dependency graph — it cost 8.3 GB the one time an agent did it.
• Never cargo clean the shared dir. You would wipe every other agent's cache, including agents mid-build. Cleaning is the orchestrator's call, made when no agents are live.

Check for room before a long build — under ~10 GB free, stop and say so:

Get-PSDrive C | Select-Object @{n='FreeGB';e={[math]::Round($_.Free/1GB,1)}}

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Before you open the PR

• cargo fmt --all --check clean
• cargo clippy clean with the right features (-D warnings)
• tests for what you touched, passing
• red-before-green evidence: your new test run against the base branch, failing — the command and the failure line go in the PR description. A test nobody has seen fail is decoration, not a safety net.
• then let CI run the matrix, and fix what it finds

Handing an unvalidated branch to a reviewer just moves the compile cost onto someone who is explicitly forbidden from paying it.