ci: use mold linker for faster CI builds

[panos-xyz]

Summary

• Install mold multi-threaded linker via rui314/setup-mold in build, clippy, and test jobs
• Pass -C link-arg=-fuse-ld=mold via RUSTFLAGS to use mold instead of default single-threaded ld
• fmt and doc-test jobs excluded (don't produce linked binaries)

Both scroll-reth and tempo use mold in CI for faster builds.

Test plan

• Build workflow completes with mold
• Clippy workflow completes with mold
• Test workflow completes with mold
• Compare CI times before/after to measure improvement

Summary by CodeRabbit

• Chores
  • CI workflows updated to install and use a faster linker and set build environment variables for consistent linking.
  • Build jobs simplified to a quicker verification step, reducing CI time; lint and test jobs also include the linker installation for consistency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 49c6a069-e4c5-4f94-acae-c8f3ca2c89ff

📥 Commits

Reviewing files that changed from the base of the PR and between 271b27f and 7d785c6.

📒 Files selected for processing (2)

• .github/workflows/build.yml
• .github/workflows/test.yml

🚧 Files skipped from review as they are similar to previous changes (2)

• .github/workflows/test.yml
• .github/workflows/build.yml

---

📝 Walkthrough

Walkthrough

CI workflows were updated to install the mold linker via rui314/setup-mold@v1 and pass -C link-arg=-fuse-ld=mold through RUSTFLAGS. The build workflow switched from running debug/release cargo build to cargo check --all --all-targets. Lint and test workflows now install mold before caching and execution.

Changes

Cohort / File(s)	Summary
Build workflow .github/workflows/build.yml	Added rui314/setup-mold@v1 step; extended RUSTFLAGS to include -C link-arg=-fuse-ld=mold; replaced dual cargo build steps with cargo check --all --all-targets.
Lint workflow .github/workflows/lint.yml	Inserted rui314/setup-mold@v1 step after Rust toolchain install and before caching/Clippy runs; RUSTFLAGS usage aligned with other workflows.
Test workflows .github/workflows/test.yml	Set global RUSTFLAGS to -C link-arg=-fuse-ld=mold; added rui314/setup-mold@v1 step in test, doc-test, and e2e jobs before caching and test steps.

Sequence Diagram(s)

sequenceDiagram
  participant Runner as GitHub Actions Runner
  participant Rust as setup-rust (toolchain + clippy)
  participant Mold as setup-mold (rui314/setup-mold@v1)
  participant Cache as actions/cache
  participant Cargo as Cargo (build/check/test)

  Runner->>Rust: install Rust toolchain (+clippy)
  Runner->>Mold: install mold linker
  Runner->>Cache: restore cache
  Runner->>Cargo: run `cargo check` / `cargo clippy` / `cargo test`
  Cargo-->>Cache: update cache
  Cargo-->>Runner: report results

Loading

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

• anylots
• chengwenxi

Poem

🐰 Hopping through CI with a hop and a thud,

I fetch the mold linker and tidy the mud.
Checks sprint along, lint gives a cheer,
I nibble the logs and vanish — see you next year! 🥕✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main objective: adopting the mold linker in CI workflows for performance improvements.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch panos/ci-mold

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[chengwenxi]

LGTM. Clean integration of mold linker via rui314/setup-mold@v1 in build/clippy/test jobs. -C link-arg=-fuse-ld=mold is the correct RUSTFLAGS approach. fmt/doc-test exclusion is reasonable.