Carrasco/.github/workflows/pr-conflict-check.yml

name: PR Conflict Check

# Detects merge conflicts between a PR branch and its base branch BEFORE the PR is
# merged (Unity .unity/.asset YAML files are especially prone to ugly conflicts).
# If the conflict check (or the workflow itself) fails, an issue is opened
# automatically so the conflict doesn't sit silently in a red PR check.

on:
  pull_request:
    types: [opened, synchronize, reopened]
    branches: [main]

permissions:
  contents: read
  issues: write

concurrency:
  group: pr-conflict-check-${{ github.event.pull_request.number }}
  cancel-in-progress: true

jobs:
  check-conflicts:
    name: Check for merge conflicts with ${{ github.event.pull_request.base.ref }}
    runs-on: ubuntu-latest
    outputs:
      conflicted_files: ${{ steps.merge_check.outputs.conflicted_files }}
    steps:
      - name: Checkout PR head
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.head.sha }}
          fetch-depth: 0

      - name: Attempt merge with base branch
        id: merge_check
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"

          git fetch origin "${{ github.event.pull_request.base.ref }}"

          if git merge --no-commit --no-ff "origin/${{ github.event.pull_request.base.ref }}"; then
            echo "No conflicts. Clean merge with base branch confirmed."
            git merge --abort || true
            exit 0
          fi

          echo "::error::Merge conflict detected against ${{ github.event.pull_request.base.ref }}"
          files=$(git diff --name-only --diff-filter=U)
          echo "Conflicted files:"
          echo "$files"

          {
            echo "conflicted_files<<EOF"
            echo "$files"
            echo "EOF"
          } >> "$GITHUB_OUTPUT"

          git merge --abort || true
          exit 1

  report-failure:
    name: Open issue on failure
    needs: check-conflicts
    if: failure()
    runs-on: ubuntu-latest
    steps:
      - name: Create or update tracking issue
        uses: actions/github-script@v7
        with:
          script: |
            const prNumber = context.payload.pull_request.number;
            const prTitle = context.payload.pull_request.title;
            const prUrl = context.payload.pull_request.html_url;
            const baseRef = context.payload.pull_request.base.ref;
            const headRef = context.payload.pull_request.head.ref;
            const runUrl = `${context.serverUrl}/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`;
            const conflictedFiles = `${{ needs.check-conflicts.outputs.conflicted_files }}`.trim();

            const title = `Merge conflict: PR #${prNumber} vs ${baseRef}`;

            const fileList = conflictedFiles
              ? conflictedFiles.split('\n').filter(Boolean).map(f => `- \`${f}\``).join('\n')
              : '_The conflict check workflow itself failed before listing files — see the run log._';

            const body = [
              `The **PR Conflict Check** workflow failed for [PR #${prNumber}](${prUrl}) ("${prTitle}").`,
              '',
              `**Branch**: \`${headRef}\` → \`${baseRef}\``,
              `**Workflow run**: ${runUrl}`,
              '',
              '**Conflicted files:**',
              fileList,
              '',
              'Rebase or merge the base branch into this PR branch locally and resolve the',
              'conflicts above, then push again. This issue will stay open until a follow-up',
              'run of the conflict check passes — close it manually once resolved.',
            ].join('\n');

            const { data: existing } = await github.rest.issues.listForRepo({
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: 'open',
              labels: 'merge-conflict',
            });

            const match = existing.find(issue => issue.title === title);

            if (match) {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: match.number,
                body: `Conflict still present as of ${runUrl}.\n\n${body}`,
              });
            } else {
              await github.rest.issues.create({
                owner: context.repo.owner,
                repo: context.repo.repo,
                title,
                body,
                labels: ['merge-conflict', 'ci-failure'],
              });
            }