pr-conflict-checker.yml

name: 'Tools: PR Conflict Checker'

on:
  # zizmor: ignore[dangerous-triggers] - intentional: needs write access for conflict labels/comments, checkout uses PR head SHA for read-only grep
  pull_request_target:
    types:
      - 'opened'
      - 'synchronize'
      - 'reopened'
    branches:
      - 'master'
      - 'v5.*'

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

permissions: {}

jobs:
  check-conflicts:
    runs-on: ubuntu-latest
    timeout-minutes: 15
    permissions:
      contents: read
      pull-requests: write
      issues: write

    steps:
      - name: Harden the runner (Audit all outbound calls)
        uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0
        with:
          egress-policy: audit

      - name: Checkout PR head
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          ref: ${{ github.event.pull_request.head.sha }}
          fetch-depth: 1
          persist-credentials: false # No write token in the untrusted PR-head tree; public repo so base fetch/changed-files work unauthenticated

      - name: Fetch PR base ref for tj-actions/changed-files
        env:
          BASE_REF: ${{ github.event.pull_request.base.ref }}
        run: git fetch --depth=1 origin "${BASE_REF}"

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@9426d40962ed5378910ee2e21d5f8c6fcbf2dd96 # v47.0.6
        with:
          files: '**'
          safe_output: false # Raw paths (list read via env var, injection-safe); default escaping backslash-quotes chars like () and breaks the -f test
          separator: "\n" # Newline-delimited so the reader tolerates spaces and glob chars in paths

      - name: Check for conflict markers
        id: conflict-check
        run: |
          echo "Checking for conflict markers in changed files..."

          CONFLICT_FILES=""
          HAS_CONFLICTS=false

          # Read newline-delimited paths so spaces/globs neither word-split nor glob-expand
          while IFS= read -r file; do
            [ -n "$file" ] || continue
            [ -f "$file" ] || continue
            echo "Checking file: $file"

            if grep -qE '^(<<<<<<<|=======|>>>>>>>)' "$file" 2>/dev/null; then
              echo "Conflict markers found in: $file"
              CONFLICT_FILES="${CONFLICT_FILES}- \`${file}\`"$'\n'
              HAS_CONFLICTS=true
            fi
          done <<< "$STEPS_CHANGED_FILES_OUTPUTS_ALL_CHANGED_FILES"

          if [ "$HAS_CONFLICTS" = true ]; then
            echo "has_conflicts=true" >> "$GITHUB_OUTPUT"
            {
              echo "conflict_files<<EOF"
              echo "$CONFLICT_FILES"
              echo "EOF"
            } >> "$GITHUB_OUTPUT"
            echo "Conflict markers detected"
          else
            echo "has_conflicts=false" >> "$GITHUB_OUTPUT"
            echo "No conflict markers found in changed files"
          fi
        env:
          STEPS_CHANGED_FILES_OUTPUTS_ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}

      - name: Check base-branch mergeability
        id: merge-check
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          REPO: ${{ github.repository }}
        run: |
          MERGEABLE=null

          # GitHub computes mergeability async, so .mergeable is null until ready; poll until resolved
          for attempt in 1 2 3 4 5; do
            MERGEABLE=$(gh api "repos/${REPO}/pulls/${PR_NUMBER}" --jq '.mergeable')
            if [ "$MERGEABLE" != "null" ]; then
              break
            fi
            echo "Attempt ${attempt}: mergeability not computed yet, retrying..."
            sleep 3
          done

          # Keep 'unknown' distinct from 'clean' so we never assert a clean merge we could not confirm
          case "$MERGEABLE" in
            false) STATUS=conflict; echo "PR branch cannot be merged cleanly into its base branch" ;;
            true)  STATUS=clean;    echo "PR branch merges cleanly into its base branch" ;;
            *)     STATUS=unknown;  echo "::warning::Mergeability did not resolve after retries; leaving it undetermined" ;;
          esac

          echo "merge_status=${STATUS}" >> "$GITHUB_OUTPUT"

      - name: Manage conflict label
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          HAS_CONFLICTS: ${{ steps.conflict-check.outputs.has_conflicts }}
          MERGE_STATUS: ${{ steps.merge-check.outputs.merge_status }}
        run: |
          LABEL_NAME="has-conflicts"

          if [ "$HAS_CONFLICTS" = "true" ] || [ "$MERGE_STATUS" = "conflict" ]; then
            echo "Adding conflict label to PR #${PR_NUMBER}..."
            gh pr edit "$PR_NUMBER" --add-label "$LABEL_NAME" --repo ${{ github.repository }} || true
          elif [ "$MERGE_STATUS" = "unknown" ]; then
            # Don't drop the label on an undetermined merge state; a later run will settle it
            echo "Mergeability undetermined; leaving label unchanged"
          else
            echo "Removing conflict label from PR #${PR_NUMBER}..."
            gh pr edit "$PR_NUMBER" --remove-label "$LABEL_NAME" --repo ${{ github.repository }} || true
          fi

      - name: Find existing comment
        uses: peter-evans/find-comment@b30e6a3c0ed37e7c023ccd3f1db5c6c0b0c23aad # v4.0.0
        id: find-comment
        with:
          issue-number: ${{ github.event.pull_request.number }}
          comment-author: 'github-actions[bot]'
          body-includes: '<!-- conflict-checker-comment -->'

      - name: Create or update comment
        uses: peter-evans/create-or-update-comment@e8674b075228eee787fea43ef493e45ece1004c9 # v5.0.0
        with:
          comment-id: ${{ steps.find-comment.outputs.comment-id }}
          issue-number: ${{ github.event.pull_request.number }}
          edit-mode: replace
          body: |
            <!-- conflict-checker-comment -->
            ${{ (steps.conflict-check.outputs.has_conflicts == 'true' || steps.merge-check.outputs.merge_status == 'conflict') && '⚠️ **Conflicts Detected**' || (steps.merge-check.outputs.merge_status == 'unknown' && 'ℹ️ **Conflict Check Incomplete**' || '✅ **No Conflicts**') }}
            ${{ steps.conflict-check.outputs.has_conflicts == 'true' && format('
            **Conflict markers** are present in the following files:

            {0}
            Resolve them by removing every `<<<<<<<`, `=======`, and `>>>>>>>` marker, then commit and push.', steps.conflict-check.outputs.conflict_files) || '' }}
            ${{ steps.merge-check.outputs.merge_status == 'conflict' && '
            **Merge conflict with the base branch.** This PR cannot be merged cleanly. Update your branch with the latest base (rebase or merge) and resolve the conflicts.' || '' }}
            ${{ steps.merge-check.outputs.merge_status == 'unknown' && '
            GitHub had not finished computing mergeability, so base-branch conflict status could not be verified on this run.' || '' }}
            ${{ (steps.conflict-check.outputs.has_conflicts != 'true' && steps.merge-check.outputs.merge_status == 'clean') && '
            No conflict markers, and the branch merges cleanly into its base.' || '' }}

      - name: Fail workflow if conflicts detected
        if: steps.conflict-check.outputs.has_conflicts == 'true' || steps.merge-check.outputs.merge_status == 'conflict'
        env:
          HAS_CONFLICTS: ${{ steps.conflict-check.outputs.has_conflicts }}
          MERGE_STATUS: ${{ steps.merge-check.outputs.merge_status }}
        run: |
          [ "$HAS_CONFLICTS" = "true" ] && echo "::error::Conflict markers detected in changed files"
          [ "$MERGE_STATUS" = "conflict" ] && echo "::error::PR branch has merge conflicts with the base branch"
          exit 1