clippy-diff-report

name	clippy-diff-report
description	Run clippy locally and report only issues in the current diff, matching the CI reviewdog flow. Use when asked how to lint changed code or get clippy feedback on a branch before pushing.

Run Clippy on the Current Diff Only

The problem

Running cargo clippy on the whole workspace produces hundreds of warnings that may have nothing to do with your changes. The CI workflow solves this with reviewdog — a tool that filters clippy output to only lines touched by the PR diff.

You can run the same filter locally before pushing.

Prerequisites

• reviewdog on PATH (provided by the devenv shell)
• Documentation EPUB already built (cargo xtask docs --mdbook-only)
• Native dependencies already built (cargo xtask setup --host)

Run clippy filtered to your diff

cargo xtask clippy --features default --github-report --diff-branch master

This:

1. Runs cargo clippy --message-format=short for the default feature set
2. Pipes output through reviewdog with -filter-mode=added
3. Reviewdog diffs against master and prints only warnings on changed lines

Why --features default

The full feature matrix is large and slow. Run the complete matrix only in CI. Locally, lint the feature combination you are actively working with. Use cargo xtask ci matrix to see all available labels if you need a specific one.

Check all feature combinations you touched

If your changes span multiple feature sets (e.g. you added #[cfg(feature = "tracing")] code), run clippy for each relevant combination:

cargo xtask clippy --features default --github-report --diff-branch master
cargo xtask clippy --features "profiling + test + tracing" --github-report --diff-branch master

[!NOTE] The telemetry feature is excluded from the xtask matrix because it aliases tracing + profiling with no separate cfg branches. Use the expanded form (profiling + test + tracing) instead.

How it works

The xtask wrapper constructs a reviewdog invocation equivalent to:

reviewdog \
  -f=clippy \
  -filter-mode=added \
  -fail-on-error=false \
  -reporter=local \
  -diff="git diff --no-ext-diff master"

• -filter-mode=added — only reports diagnostics on lines that appear in the diff (new or modified lines)
• -reporter=local — prints to terminal instead of posting GitHub comments
• -diff=... — tells reviewdog which diff to filter against

Common use cases

Goal	Command
Check default-feature changes before pushing	cargo xtask clippy --features default --github-report --diff-branch master
Check telemetry-related changes	cargo xtask clippy --features "profiling + test + tracing" --github-report --diff-branch master
See raw (unfiltered) clippy output for one feature set	cargo xtask clippy --features default
Run the full matrix (slow — CI only)	cargo xtask clippy --github-report --diff-branch master (omits --features)

Troubleshooting

"reviewdog not found"

• Using devenv: reviewdog is already provided by the devenv shell. Ensure you are inside the shell (direnv allow or devenv shell).
• Not using devenv: Install reviewdog yourself. The simplest way is via Homebrew (brew install reviewdog) or by downloading the binary from https://github.com/reviewdog/reviewdog/releases. If you are unsure how to install it on your platform, ask the operator for help.

"diff-branch: no merge base"

Your branch may be old. Rebase or merge master first:

git fetch origin master
git rebase origin/master

Too much noise from unrelated files

You probably forgot --diff-branch. Without it, xtask falls back to the github-pr-review reporter which tries to fetch the PR diff from GitHub and will fail locally.