auto-milestone.yaml

name: Auto-assign milestone

on:
    issues:
        types: [opened]

env:
    MILESTONE_NAME: '4.x'

jobs:
    assign-milestone:
        runs-on: ubuntu-latest
        permissions:
            issues: write
        steps:
            - name: Assign milestone
              uses: actions/github-script@v8
              with:
                  script: |
                      const owner = context.repo.owner;
                      const repo = context.repo.repo;
                      
                      // Pagination-safe fetch of open milestones
                      const milestones = await github.paginate(
                        github.rest.issues.listMilestones,
                        { owner, repo, state: 'open', per_page: 100 }
                      );
                      
                      const name = process.env.MILESTONE_NAME;
                      const target = milestones.find(m => m.title === name);
                      
                      if (!target) {
                        core.warning(`Milestone '${name}' not found among open milestones.`);
                        return;
                      }
                      
                      await github.rest.issues.update({
                        owner,
                        repo,
                        issue_number: context.issue.number,
                        milestone: target.number,
                      });
                      
                      core.info(`Assigned milestone '${name}' (#${target.number}) to issue #${context.issue.number}.`);