check-api-compatibility.yml

# This workflow makes sure that a pull request does not make any incompatible changes
# to the public API of Gson
name: Check API compatibility

on: pull_request

jobs:
  check-api-compatibility:
    runs-on: ubuntu-latest

    # This setup tries to determine API incompatibility only for the changes introduced by the
    # pull request. It does this by first checking out the 'old' version and installing it into
    # the local Maven repository before then using japicmp to compare it to the current changes.
    #
    # Alternatively it would also be possible to compare against the last release version instead.
    #
    # Both approaches have their advantages and disadvantages, see description of
    # https://github.com/google/gson/pull/2692 for details.

    steps:
      - name: Check out old version
        uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29  # v4.1.6
        with:
          ref: ${{ github.event.pull_request.base.sha }}
          path: 'gson-old-japicmp'

      - name: Set up JDK 11
        uses: actions/setup-java@99b8673ff64fbf99d8d325f52d9a5bdedb8483e9  # v4.2.1
        with:
          distribution: 'temurin'
          java-version: '11'
          cache: 'maven'

      - name: Build old version
        run: |
          cd gson-old-japicmp
          # Set dummy version
          mvn --batch-mode --no-transfer-progress org.codehaus.mojo:versions-maven-plugin:2.16.2:set "-DnewVersion=0.0.0-JAPICMP-OLD"
          # Install artifacts with dummy version in local repository; used later by Maven plugin for comparison
          mvn --batch-mode --no-transfer-progress install -DskipTests

      - name: Check out new version
        uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29  # v4.1.6

      - name: Check API compatibility
        id: check-compatibility
        run: |
          mvn --batch-mode --fail-at-end --no-transfer-progress package japicmp:cmp -DskipTests

      - name: Upload API differences artifacts
        uses: actions/upload-artifact@65462800fd760344b1a7b4382951275a0abb4808  # v4.3.3
        # Run on workflow success (in that case differences report might include added methods and classes)
        # or when API compatibility check failed
        if: success() || ( failure() && steps.check-compatibility.outcome == 'failure' )
        with:
          name: api-differences
          path: |
            **/japicmp/default-cli.html
            **/japicmp/default-cli.diff
          # Plugin should always have created report files (though they might be empty)
          if-no-files-found: error