Conventional Commits → Semver Bump Calculator

conventional-semver

# ============================================================================
# Conventional Commits → Semver Bump Calculator
# ============================================================================
# Drop this into your workflow. On PR merge to main, it reads the commits
# from the merged PR and outputs the bump type (major|minor|patch) plus
# the next version string.
#
# Follows the Conventional Commits v1.0.0 spec:
#   - fix:          → patch
#   - feat:         → minor
#   - BREAKING CHANGE: (footer) or feat!:/fix!:/etc. → major
#   - Anything else (chore, docs, ci, etc.) → patch (safe default)
#
# Outputs:
#   steps.semver.outputs.bump       → major | minor | patch
#   steps.semver.outputs.version    → e.g. 1.3.0
#   steps.semver.outputs.previous   → e.g. 1.2.4
#
# Prerequisites:
#   - CURRENT_VERSION env var: set this to your artifact's current version.
#     Pull it from wherever you track it — a VERSION file, your last Nexus
#     tag, a git tag, whatever. The snippet doesn't care where it comes from.
# ============================================================================

name: Build on PR Merge

on:
  pull_request:
    types: [closed]
    branches: [main]

jobs:
  build:
    if: github.event.pull_request.merged == true
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4
        with:
          # Fetch full history so we can read the PR's commits
          fetch-depth: 0

      # ----------------------------------------------------------------
      # Set your current version here. Replace this with however you
      # track it — VERSION file, last Nexus tag, git tag, etc.
      # ----------------------------------------------------------------
      # Examples:
      #   CURRENT_VERSION=$(cat VERSION)
      #   CURRENT_VERSION=$(curl -s https://nexus.example.com/api/latest/my-image | jq -r .version)
      #   CURRENT_VERSION=$(git tag -l 'my-service-v*' --sort=-v:refname | head -1 | sed 's/my-service-v//')
      # ----------------------------------------------------------------

      - name: Calculate semver bump from PR commits
        id: semver
        env:
          CURRENT_VERSION: "0.0.0"  # ← replace with your lookup
          PR_BASE_SHA: ${{ github.event.pull_request.base.sha }}
          PR_HEAD_SHA: ${{ github.event.pull_request.head.sha }}
        run: |
          set -euo pipefail

          echo "::group::PR Commits"
          # Get commit messages from this PR only (base...head)
          COMMITS=$(git log --format="%s%n%b" "${PR_BASE_SHA}..${PR_HEAD_SHA}")
          echo "$COMMITS"
          echo "::endgroup::"

          # Determine bump type — highest wins
          BUMP="patch"

          while IFS= read -r line; do
            # Skip empty lines
            [[ -z "$line" ]] && continue

            # Major: BREAKING CHANGE footer or ! after type
            if echo "$line" | grep -qE '^BREAKING CHANGE:|^BREAKING-CHANGE:'; then
              BUMP="major"
              break
            fi
            if echo "$line" | grep -qE '^[a-z]+(\(.+\))?!:'; then
              BUMP="major"
              break
            fi

            # Minor: feat
            if echo "$line" | grep -qE '^feat(\(.+\))?:'; then
              [[ "$BUMP" != "major" ]] && BUMP="minor"
            fi

            # patch: fix, or anything else with a type — already the default

          done <<< "$COMMITS"

          # Apply bump to current version
          IFS='.' read -r MAJOR MINOR PATCH <<< "$CURRENT_VERSION"
          MAJOR=${MAJOR:-0}; MINOR=${MINOR:-0}; PATCH=${PATCH:-0}

          case "$BUMP" in
            major) MAJOR=$((MAJOR + 1)); MINOR=0; PATCH=0 ;;
            minor) MINOR=$((MINOR + 1)); PATCH=0 ;;
            patch) PATCH=$((PATCH + 1)) ;;
          esac

          NEXT_VERSION="${MAJOR}.${MINOR}.${PATCH}"

          echo "Previous : $CURRENT_VERSION"
          echo "Bump     : $BUMP"
          echo "Next     : $NEXT_VERSION"

          # Set outputs for downstream steps
          echo "bump=$BUMP"             >> "$GITHUB_OUTPUT"
          echo "version=$NEXT_VERSION"  >> "$GITHUB_OUTPUT"
          echo "previous=$CURRENT_VERSION" >> "$GITHUB_OUTPUT"

      # ----------------------------------------------------------------
      # Use the outputs downstream, e.g.:
      # ----------------------------------------------------------------
      # - name: Build and push image
      #   run: |
      #     docker build -t my-registry/my-image:${{ steps.semver.outputs.version }} .
      #     docker push my-registry/my-image:${{ steps.semver.outputs.version }}
      # ----------------------------------------------------------------