.github/workflows/no-main-prs.yaml

# Copyright 2013 The Flutter Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

name: No PRs on main

on:
  # Safe because this workflow does not check out code or run arbitrary scripts.
  # It only checks the PR target branch and comments/fails if targeting main.
  pull_request_target: # zizmor: ignore[dangerous-triggers]
    types: [opened, synchronize, reopened, edited]

permissions: read-all

jobs:
  reject-main-prs:
    runs-on: ubuntu-latest
    if: ${{ github.repository == 'flutter/flutter' }}
    permissions:
      contents: read
      pull-requests: write

    steps:
      - name: Comment on PRs targeting main
        if: github.base_ref == 'main'
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          github-token: ${{ github.token }}
          script: |
            const issueNumber = context.issue.number;
            const comments = await github.paginate(github.rest.issues.listComments, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: issueNumber,
            });
            const docUrl = 'https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-base-branch-of-a-pull-request';
            const alreadyCommented = comments.some(comment =>
              comment.body && comment.body.includes(docUrl)
            );
            if (!alreadyCommented) {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: issueNumber,
                body: 'This pull request targets the `main` branch, but the primary branch for this repository is `master`.\n\n' +
                  'Please change the base branch of this pull request to `master`.\n\n' +
                  `See: ${docUrl}`,
              });
            }

      - name: Check base branch
        env:
          # Explicitly fallback to an empty string if it doesn't exist
          TARGET_BRANCH: ${{ github.base_ref || ''}}
        run: |
          if [ "$TARGET_BRANCH" = "main" ]; then
            echo "::error::Do not open PRs on \`main\`. The primary branch is \`master\`. You can change the base branch of this PR to \`master\`. See: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-base-branch-of-a-pull-request"
            exit 1
          fi