sync-milestone.yml

name: Sync Milestone from Issue
on:
  pull_request:
    types: [opened, edited, reopened]

jobs:
  sync-milestone:
    runs-on: ubuntu-latest
    permissions:
      issues: read
      pull-requests: write
    steps:
      - name: Sync Milestone
        env:
          GH_TOKEN: ${{ github.token }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          REPO: ${{ github.repository }}
          OWNER: ${{ github.repository_owner }}
        run: |
          # 1. Get the milestone of the officially linked issues and the PR's current milestone via GraphQL
          # This catches issues linked via "Fixes #123" and similar in the body or the UI sidebar.
          API_RESPONSE=$(gh api graphql -f query='
            query($owner: String!, $name: String!, $pr: Int!) {
              repository(owner: $owner, name: $name) {
                pullRequest(number: $pr) {
                  milestone {
                    number
                  }
                  closingIssuesReferences(first: 1) {
                    nodes {
                      milestone {
                        number
                        title
                      }
                    }
                  }
                }
              }
            }' -F owner="$OWNER" -F name="${REPO#*/}" -F pr=$PR_NUMBER)

          MILESTONE_NUMBER=$(echo "$API_RESPONSE" | jq -r '.data.repository.pullRequest.closingIssuesReferences.nodes[0].milestone.number // "null"')
          MILESTONE_TITLE=$(echo "$API_RESPONSE" | jq -r '.data.repository.pullRequest.closingIssuesReferences.nodes[0].milestone.title // "null"')
          CURRENT_PR_MILESTONE=$(echo "$API_RESPONSE" | jq -r '.data.repository.pullRequest.milestone.number // "null"')

          # 2. Check if a milestone was found
          if [ "$MILESTONE_NUMBER" != "null" ] && [ -n "$MILESTONE_NUMBER" ]; then
            if [ "$MILESTONE_NUMBER" = "$CURRENT_PR_MILESTONE" ]; then
              echo "PR already has milestone '$MILESTONE_TITLE' set. No update needed."
            else
              echo "Found milestone '$MILESTONE_TITLE' from linked issue. Assigning to PR..."
              gh pr edit $PR_NUMBER --milestone "$MILESTONE_TITLE" --repo "$REPO"
            fi
          else
            echo "No milestone found on linked issues or no issues linked."
          fi