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@v7
        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. When the base commit is missing from the clone the action fails with an explicit error instead of reporting "no change" (which used to skip every downstream job).
• Per-app boolean outputs (changed-api, changed-web, changed-client) are useful for if: conditions when you don't need a matrix. Composite actions cannot declare outputs dynamically, so only these three names exist; for any other app test changed-apps, e.g. contains(fromJson(steps.changes.outputs.changed-apps), 'admin').
• App names are sanitized (lowercased, non-alphanumeric characters replaced with _) in the output key names.