Script to checkout a GitHub PR branch from a fork and push it to a new branch in target repo. This is useful for testing PRs from forks in the main repository.

copy-pr branch-from-fork.sh

#!/bin/bash
# Script to checkout a GitHub PR branch from a fork and push it to a new branch in target repo
# This is useful for testing PRs from forks in the main repository.

set -euo pipefail

# Check if PR URL is provided
if [ $# -eq 0 ]; then
  echo "Usage: $0 <github-pr-url>"
  echo "Example: $0 https://github.com/owner/repo/pull/123"
  exit 1
fi

PR_URL="$1"

# Extract owner, repo, and PR number from URL
if [[ ! "$PR_URL" =~ github\.com/([^/]+)/([^/]+)/pull/([0-9]+) ]]; then
  echo "Error: Invalid GitHub PR URL format"
  echo "Expected format: https://github.com/owner/repo/pull/NUMBER"
  exit 1
fi

OWNER="${BASH_REMATCH[1]}"
REPO="${BASH_REMATCH[2]}"
PR_NUMBER="${BASH_REMATCH[3]}"

echo "Fetching PR information for $OWNER/$REPO#$PR_NUMBER..."

# Get PR information using gh CLI
PR_INFO=$(gh pr view "$PR_NUMBER" --repo "$OWNER/$REPO" --json headRefName,headRepository,headRepositoryOwner,baseRefName,isCrossRepository)

# Extract branch name and repository information
HEAD_BRANCH=$(echo "$PR_INFO" | jq -r '.headRefName')
HEAD_REPO_NAME=$(echo "$PR_INFO" | jq -r '.headRepository.name')
HEAD_REPO_OWNER=$(echo "$PR_INFO" | jq -r '.headRepositoryOwner.login')
IS_CROSS_REPO=$(echo "$PR_INFO" | jq -r '.isCrossRepository')
BASE_REPO="$OWNER/$REPO" # The base repo is the one we're querying

# Construct head repository name
if [ "$IS_CROSS_REPO" = "true" ]; then
  HEAD_REPO="$HEAD_REPO_OWNER/$HEAD_REPO_NAME"
else
  HEAD_REPO="$BASE_REPO"
fi

echo "Source branch: $HEAD_BRANCH"
echo "Source repo: $HEAD_REPO"
echo "Target repo: $BASE_REPO"

NEW_BRANCH_NAME="pr-$PR_NUMBER-$HEAD_BRANCH"
echo "New branch name: $NEW_BRANCH_NAME"

# Check if we need to clone the target repository
if ! git rev-parse --is-inside-work-tree &>/dev/null; then
  # Create temp directory and clone target repository
  TEMP_DIR=$(mktemp -d)
  echo "Creating temporary directory: $TEMP_DIR"
  cd "$TEMP_DIR"

  echo "Cloning target repository..."
  git clone "https://github.com/$OWNER/$REPO.git"
  cd "$REPO"

  # Set cleanup trap
  trap "rm -rf '$TEMP_DIR'" EXIT
fi

# Add the source repository as a remote if it's different from the base repo
if [ "$HEAD_REPO" != "$BASE_REPO" ]; then
  REMOTE_NAME="pr-source-$PR_NUMBER"
  echo "Adding remote for source repository..."
  echo "DEBUG: Adding remote $REMOTE_NAME with URL https://github.com/$HEAD_REPO.git"

  # Remove existing remote if it exists
  git remote remove "$REMOTE_NAME" 2>/dev/null || true

  git remote add "$REMOTE_NAME" "https://github.com/$HEAD_REPO.git"
  git fetch "$REMOTE_NAME"
  SOURCE_REF="$REMOTE_NAME/$HEAD_BRANCH"
else
  git fetch origin
  SOURCE_REF="origin/$HEAD_BRANCH"
fi

# Checkout the PR branch
echo "Checking out branch $HEAD_BRANCH..."
git checkout -b "$NEW_BRANCH_NAME" "$SOURCE_REF"

# Push the new branch to origin
echo "Pushing new branch $NEW_BRANCH_NAME to origin..."
git push -u origin "$NEW_BRANCH_NAME"

echo "Successfully created and pushed branch: $NEW_BRANCH_NAME"
echo "Branch is now available in the target repository"

# Clean up remote if we added one
if [ "$HEAD_REPO" != "$BASE_REPO" ]; then
  git remote remove "$REMOTE_NAME"
  echo "Cleaned up temporary remote: $REMOTE_NAME"
fi