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: ${{ github.repository_owner }}
        run: |
          # 1. Get milestones from ALL linked closing issues and the PR's current milestone via GraphQL.
          #    closingIssuesReferences catches issues linked via "Fixes #123" and similar in the body or sidebar.
          API_RESPONSE=$(gh api graphql -f query='
            query($owner: String!, $name: String!, $pr: Int!) {
              repository(owner: $owner, name: $name) {
                pullRequest(number: $pr) {
                  milestone {
                    number
                    title
                  }
                  closingIssuesReferences(first: 20) {
                    nodes {
                      milestone {
                        number
                        title
                      }
                    }
                  }
                }
              }
            }' -F owner="$OWNER" -F name="${REPO#*/}" -F pr=$PR_NUMBER)

          # 2. Collect all X.Y.Z milestone titles from linked issues, dedupe, version-sort, pick highest.
          MILESTONE_TITLE=$(echo "$API_RESPONSE" \
            | jq -r '.data.repository.pullRequest.closingIssuesReferences.nodes[].milestone.title // empty' \
            | grep -E '^[0-9]+\.[0-9]+\.[0-9]+$' \
            | sort -uV \
            | tail -n1)

          CURRENT_PR_MILESTONE_TITLE=$(echo "$API_RESPONSE" | jq -r '.data.repository.pullRequest.milestone.title // "null"')

          # 3. No qualifying milestone found across all linked issues.
          if [ -z "$MILESTONE_TITLE" ]; then
            echo "No X.Y.Z milestone found on any linked issue. Nothing to sync."
            exit 0
          fi

          # 4. PR already has that exact milestone title — nothing to do.
          if [ "$MILESTONE_TITLE" = "$CURRENT_PR_MILESTONE_TITLE" ]; then
            echo "PR already has milestone '$MILESTONE_TITLE' set. No update needed."
            exit 0
          fi

          echo "Candidate milestone: '$MILESTONE_TITLE' (current PR milestone: '$CURRENT_PR_MILESTONE_TITLE')"

          # 5. Confirm the milestone title exists as an OPEN milestone on this repo.
          #    gh pr edit --milestone only accepts open milestones; closed ones return "not found".
          REPO_MILESTONE_MATCH=$(gh api "repos/$REPO/milestones?per_page=100&state=open" --paginate \
            | jq -r '.[].title' \
            | grep -Fx "$MILESTONE_TITLE" || true)

          if [ -z "$REPO_MILESTONE_MATCH" ]; then
            echo "::warning::Milestone '$MILESTONE_TITLE' not found as an open milestone on $REPO (it may be closed or deleted). Skipping PR milestone update."
            exit 0
          fi

          # 6. Assign milestone to PR — treat any failure as a warning, never fail the job.
          echo "Assigning milestone '$MILESTONE_TITLE' to PR #$PR_NUMBER..."
          if ! gh pr edit "$PR_NUMBER" --milestone "$MILESTONE_TITLE" --repo "$REPO"; then
            echo "::warning::Failed to assign milestone '$MILESTONE_TITLE' to PR #$PR_NUMBER. Manual update may be needed."
          fi
          exit 0