Automate milestone assignment to merged pr's

milestone.yaml

# File: .github/workflows/auto-milestone.yml
name: Auto-Assign Next-Minor Milestone

on:
  pull_request:
    types: [closed]

jobs:
  add-milestone:
    if: ${{ github.event.pull_request.merged == true }}
    runs-on: ubuntu-latest

    steps:
      - name: Checkout repo
        uses: actions/checkout@v4

      - name: Set up Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '18'

      - name: Install dependencies
        run: npm install semver

      - name: Determine latest release tag
        id: get_latest
        run: |
          # Fetch all tags
          git fetch --tags
          # List tags sorted by semver, take the latest
          latest_tag=$(git tag -l 'v*.*.*' --sort=-v:refname | head -n1)
          echo "latest=$latest_tag" >> "$GITHUB_OUTPUT"

      - name: Compute next minor version
        id: bump_version
        run: |
          node <<'EOF'
          const semver = require('semver');
          const latest = process.env.INPUT_LATEST;
          if (!latest) {
            console.error('No valid semver tag found.');
            process.exit(1);
          }
          const next = semver.inc(latest, 'minor');
          console.log(`next=${next}`);
          EOF
        env:
          INPUT_LATEST: ${{ steps.get_latest.outputs.latest }}
        shell: bash
        continue-on-error: false
        run: |
          # This block prints "next=x.y.z" for GITHUB_OUTPUT
          node <<'EOF'
          const semver = require('semver');
          const { latest } = process.env;
          const next = semver.inc(latest, 'minor');
          console.log(`::set-output name=next::${next}`);
          EOF

      - name: Check for existing milestone
        id: find_milestone
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const { data: milestones } = await github.issues.listMilestones({
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'open'
            });
            const title = `v${process.env.NEXT}`;
            const ms = milestones.find(m => m.title === title);
            return ms ? ms.number : null;
        env:
          NEXT: ${{ steps.bump_version.outputs.next }}

      - name: Create milestone if missing
        if: ${{ steps.find_milestone.outputs.result == 'null' }}
        id: create_milestone
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const title = `v${process.env.NEXT}`;
            const { data: milestone } = await github.issues.createMilestone({
              owner: context.repo.owner,
              repo: context.repo.repo,
              title,
              state: 'open'
            });
            return milestone.number;
        env:
          NEXT: ${{ steps.bump_version.outputs.next }}

      - name: Determine milestone number
        run: |
          echo "milestone_number=${{ steps.find_milestone.outputs.result || steps.create_milestone.outputs.result }}" >> $GITHUB_OUTPUT

      - name: Assign milestone to PR
        uses: actions/github-script@v7
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const milestone_number = parseInt(process.env.MILESTONE_NUMBER, 10);
            const pr_number = context.payload.pull_request.number;
            await github.issues.update({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: pr_number,
              milestone: milestone_number
            });
        env:
          MILESTONE_NUMBER: ${{ steps.determine_milestone_number.outputs.milestone_number }}