Rust CI Pipeline Best Practices

This skill covers the design patterns for a robust Rust CI pipeline, based on production experience with multi-job workflows.

Six-Job Architecture

lint ──┐
msrv ──┤
test ──┼──→ ci (gate)
deny ──┤
audit ─┘

Job	Purpose	Blocking?
lint	cargo fmt --check + cargo clippy (default + all features)	Yes
msrv	cargo check --locked with pinned MSRV toolchain	Yes
test	cargo test across OS matrix (Linux/macOS/Windows) + beta	Yes
deny	cargo-deny for advisories, bans, licenses, sources	Mixed*
audit	cargo audit for known vulnerabilities	Yes
ci	Gate job — single required status check	Always runs

*deny uses continue-on-error for advisories (informational) but blocks on bans/licenses/sources.

Gate Job Pattern

The ci gate job is the only required status check in branch protection settings:

ci:
  name: CI
  if: always()
  needs: [lint, msrv, test, deny, audit]
  runs-on: ubuntu-latest
  steps:
    - name: Evaluate results
      run: |
        result="${{ contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled') }}"
        [[ "$result" == "false" ]] || exit 1

Why this pattern:

• Adding/removing jobs doesn't require updating branch protection
• if: always() ensures the gate runs even if upstream jobs are cancelled
• Single check to configure in GitHub Settings

Action SHA Pinning

All actions MUST be pinned to full commit SHA with a version comment:

# v6.0.2
uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd

Why SHA not tag:

• Tags can be moved (force-pushed) by the action owner or an attacker with write access
• SHA is immutable — ensures reproducible builds
• Scorecard checks for this (Pinned-Dependencies)

Real-world incident — Trivy tag hijacking (March 2026): Attackers with write access to aquasecurity/trivy-action force-pushed 75 of 76 version tags to point to malicious commits. The poisoned entrypoint.sh harvested secrets from CI runner process memory and exfiltrated them to a typosquatting C2 domain (scan.aquasecurtiy[.]org). Over 10,000 workflow files on GitHub referenced aquasecurity/trivy-action by tag. Any pipeline that ran a poisoned tag had all accessible secrets stolen. SHA-pinned workflows were completely unaffected — the immutable commit reference couldn't be redirected. This incident is the single strongest argument for SHA pinning.

Finding the SHA for a tag:

# Get the commit SHA for a specific tag
gh api repos/actions/checkout/git/ref/tags/v4 --jq '.object.sha'

# Or browse to the tag on GitHub and copy the full SHA

Exception: SLSA generator must use @tag — see slsa-provenance skill.

Caching Strategy

- name: Cache
  uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2
  with:
    save-if: ${{ github.ref == 'refs/heads/main' }}     # Only save on main
    shared-key: msrv                                      # Share across MSRV jobs

Key decisions:

• save-if: main — PRs read the cache but don't write, preventing cache pollution
• shared-key — MSRV and stable builds share caches when possible
• Fuzz targets use workspaces: fuzz -> target and per-target keys

Permissions

Always set permissions: read-all at the workflow level:

permissions: read-all

Override per-job only where needed:

jobs:
  publish:
    permissions:
      contents: read
      id-token: write  # For OIDC Trusted Publishing

This satisfies the Scorecard Token-Permissions check and follows least privilege.

Concurrency Control

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: ${{ github.event_name == 'pull_request' }}

• Groups by workflow + branch/tag ref
• Cancels in-progress runs only for PRs (not main pushes)
• Prevents redundant CI runs on rapid PR updates

Advisory Handling

Advisories (CVE disclosures in dependencies) should NOT block PRs:

deny:
  strategy:
    matrix:
      checks:
        - advisories
        - bans licenses sources
  continue-on-error: ${{ matrix.checks == 'advisories' }}

Why: A new advisory can appear at any time, blocking all PRs until a dependency is updated. The advisory check runs but failures are informational. The bans/licenses/sources check is strict.

cargo-audit Installation

- name: Install cargo-audit
  run: cargo install cargo-audit --version 0.22.1 --locked

Gotcha: Without --locked, transitive dependencies (e.g., smol_str) may require a newer Rust version than CI provides, causing build failures. Always use --locked. Pin --version to avoid pulling untested new releases in CI — update intentionally when ready.

Test Matrix

strategy:
  fail-fast: false
  matrix:
    os: [ubuntu-latest, macos-latest, windows-latest]
    toolchain: [stable]
    include:
      - os: ubuntu-latest
        toolchain: beta

• fail-fast: false — don't cancel other OS tests if one fails
• Beta toolchain on Linux catches upcoming breakage early
• All tests use --locked to ensure reproducible builds

MSRV Verification

msrv:
  name: MSRV (1.82)
  steps:
    - uses: dtolnay/rust-toolchain@SHA
      with:
        toolchain: "1.82"
    - run: cargo check --locked
    - run: cargo check --locked --all-features

• Uses cargo check (not cargo test) — faster, only verifies compilation
• Tests both default and all-features configurations
• Pin MSRV in rust-toolchain.toml for contributor consistency

Template

See templates/workflows/ci.yml for the complete implementation.