CI on a monorepo

One repo, many packages. A PR usually touches one or two of them, but a naive cha analyze walks the whole tree and bills you for the rest.

Two strategies, often combined.

Strategy 1: analyze only changed files

cha analyze --diff runs against files modified in the working tree. In a PR pipeline, point it at the PR diff:

# Local: files changed against the working tree
cha analyze --diff

# CI: a PR diff piped in
gh pr diff "$PR_NUMBER" | cha analyze --stdin-diff --fail-on warning

--stdin-diff accepts unified-diff format on stdin. The same .cha.toml applies; only the file list narrows.

A GitHub Actions step:

- name: cha (PR diff)
  run: |
    gh pr diff ${{ github.event.pull_request.number }} \
      | cha analyze --stdin-diff --fail-on warning
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

Push events get the full analyze on the affected paths:

- name: cha (push)
  run: cha analyze --fail-on warning

Strategy 2: per-package config

If the monorepo has packages/api, packages/web, packages/shared, give each package its own .cha.toml and run Cha per-package:

for pkg in packages/*/; do
  ( cd "$pkg" && cha analyze --fail-on warning ) || exit 1
done

Each .cha.toml is independent. The shared library can keep stricter max_function_lines; the experimental package can relax complexity. There's no inheritance, deliberately — config drift between packages is a feature when packages have different shapes.

Combine: baseline per package + diff in PR

The pattern that scales:

  1. Each package has its own .cha/baseline.json, generated once when Cha was adopted.

  2. PR runs use both --baseline and --stdin-diff:

    cha analyze --stdin-diff \
  --baseline .cha/baseline.json \
  --fail-on warning < diff.patch

  3. Push to main runs the full analyze with --baseline only — catches drift even when no individual file changed.

Old findings are silenced by the baseline. New findings on changed lines fail CI. Untouched code outside the diff is skipped.

Caching

Cha caches parsed AST + finding results to .cha/cache/. In CI, cache that directory between runs:

- uses: actions/cache@v4
  with:
    path: .cha/cache
    key: cha-${{ hashFiles('**/Cargo.lock', '**/package-lock.json', '**/go.sum') }}

The cache key picks up dependency changes; finer-grained keys aren't worth the complexity.

See also