chore: Rust format and testing in CI

[aclauer]

Problem

Need to run Rust formatting checks and tests in CI

Closes DIM-938

Solution

Added auto discovery job to find all Rust workspaces in the repository based on Cargo.lock. Then run cargo fmt, cargo clippy, cargo test in all work spaces in parallel.

How to Test

Run in CI, result of all three commands matches local results. All workspaces are automatically detected without any hardcoded paths.

Contributor License Agreement

• I have read and approved the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!

[greptile-apps]

Greptile Summary

This PR adds a rust CI job that auto-discovers all Cargo workspaces in the repo by searching for Cargo.lock files, then sequentially runs cargo fmt --check, cargo clippy, and cargo test in each workspace. The job is wired into ci-complete so it gates branch protection.

• Auto-discovery: find locates every Cargo.lock outside target/, .venv/, node_modules/, and .git/, extracting parent directories as workspace roots — no hardcoded paths needed.
• Consistent flags: all three Cargo commands use --workspace (or --all for fmt) and --locked, ensuring full workspace coverage and reproducible builds.
• Empty-workspace safety: the for-loop approach, rather than a matrix, means an empty workspace list simply skips all loop bodies and exits 0 — avoiding the "matrix must have at least one element" error that a matrix strategy would trigger.

Confidence Score: 5/5

Safe to merge — the new rust CI job correctly discovers workspaces, runs all three checks with workspace-scoped flags, and integrates cleanly with ci-complete.

The implementation is straightforward and avoids the matrix-empty-list pitfall by using a for loop. All three Cargo commands use consistent, workspace-wide flags. The only note is that unquoted $CRATES expansion would misbehave for paths with spaces, which is very unlikely in practice but easy to harden.

No files require special attention.

Important Files Changed

Filename	Overview
.github/workflows/ci.yml	Adds a new rust job that auto-discovers Cargo workspaces via find/Cargo.lock, installs the stable toolchain with rustfmt+clippy, and runs cargo fmt, cargo clippy, and cargo test sequentially for each workspace; also wires rust into ci-complete.

Sequence Diagram

sequenceDiagram
    participant GHA as GitHub Actions
    participant find as find (Cargo.lock)
    participant toolchain as dtolnay/rust-toolchain
    participant cache as Swatinem/rust-cache
    participant cargo as cargo (per workspace)

    GHA->>find: Search repo for Cargo.lock files
    find-->>GHA: Newline-separated workspace paths → GITHUB_OUTPUT
    GHA->>toolchain: Install stable + rustfmt + clippy
    GHA->>cache: Cache cargo build (workspaces list)
    loop For each workspace path
        GHA->>cargo: cargo fmt --all -- --check
        cargo-->>GHA: exit 0 / non-zero
        GHA->>cargo: cargo clippy --workspace --all-targets --all-features --locked -D warnings
        cargo-->>GHA: exit 0 / non-zero
        GHA->>cargo: cargo test --workspace --all-features --locked
        cargo-->>GHA: exit 0 / non-zero
    end
    GHA->>GHA: ci-complete evaluates rust job result

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_{Reviews (5): Last reviewed commit: "Merge branch 'main' into andrew/chore/ru..." | Re-trigger Greptile}

[leshy]

@Dreamsorcerer can you review?

[Dreamsorcerer]

One blocking detail here I think. I don't think we should be using a matrix here, atleast from what I see of the current run.

Currently, this results in 3 separate jobs, requiring 3 workers. Each job only takes ~20s with about 50% of that time doing the setup/teardown of the job.

So currently this is basically 3 x 20s, instead of 1 x 40s. The difference today is neglible, but if we start adding in more crates over time, then this will lead to worker starvation and delay the other (slower) test jobs.

[leshy]

oops I approved, but disabled auto-merge, letting you guys decide, just ping me when you need approval

[aclauer]

That's a good point, I'll change that

[aclauer]

should be fixed now, also removed the separate discover job