Action — detect-changes

Detects which subdirectories under apps/ (or a custom directory) have changed since the last commit, and outputs a JSON matrix for use in downstream matrix jobs.

Usage

jobs:
  detect:
    runs-on: ubuntu-latest
    outputs:
      changed-apps: ${{ steps.changes.outputs.changed-apps }}
      has-changes:  ${{ steps.changes.outputs.has-changes }}
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: KevinDeBenedetti/github-workflows/.github/actions/detect-changes@main
        id: changes
        with:
          apps-directory: apps

  build:
    needs: detect
    if: needs.detect.outputs.has-changes == 'true'
    strategy:
      matrix:
        app: ${{ fromJson(needs.detect.outputs.changed-apps) }}
    runs-on: ubuntu-latest
    steps:
      - run: echo "Building ${{ matrix.app }}"

Inputs

Input	Type	Default	Description
apps-directory	string	apps	Root directory containing app subdirectories
base-ref	string	''	Base git ref to compare against (auto-detected if empty)

Outputs

Output	Description
changed-apps	JSON array of changed app names, e.g. ["api","web"]
has-changes	"true" or "false" — whether any app changed
changed-api	"true" or "false" — whether apps/api changed
changed-web	"true" or "false" — whether apps/web changed
changed-client	"true" or "false" — whether apps/client changed

Base ref resolution

1. Uses base-ref input if provided
2. Falls back to github.event.pull_request.base.sha on pull requests
3. Falls back to github.event.before on push events
4. Falls back to HEAD~1 if the before SHA is empty or all zeros (e.g. first push to branch)

Notes

• Requires fetch-depth: 0 (or at least enough history to compare against the base ref) in your checkout step.
• Per-app boolean outputs (changed-api, changed-web, changed-client) are useful for if: conditions when you don't need a matrix.
• App names are sanitized (lowercased, non-alphanumeric characters replaced with _) in the output key names.