rebase-main.py

#!/usr/bin/env python3

# https://claude.site/artifacts/39d84a1a-23fa-498d-a31b-7ada990a85db
# https://claude.ai/chat/097db2b0-18a9-4845-9586-f2f4bb10ac8b
#
# > Please write a python script that git fetches only main without
# > switching to it.  Then rebase the current branch atop main.  All
# > the commits after the merge-base w.r.t main should get rebased.
#
# > Oh, on further thought explicitly querying the merge-base is
# > unnecessary, it can just be git rebase main.  Also, this should
# > check if a main branch exists, and use that, otherwise check if a
# > master branch and instead use that.

import subprocess
import sys

def run_git_command(command):
    """Execute a git command and return its output"""
    try:
        result = subprocess.run(command,
                              check=True,
                              capture_output=True,
                              text=True)
        return result.stdout.strip()
    except subprocess.CalledProcessError as e:
        print(f"Error executing command {' '.join(command)}: {e.stderr}")
        sys.exit(1)

def branch_exists(branch_name):
    """Check if a branch exists locally or remotely"""
    try:
        run_git_command(['git', 'rev-parse', '--verify', branch_name])
        return True
    except:
        try:
            run_git_command(['git', 'rev-parse', '--verify', f'origin/{branch_name}'])
            return True
        except:
            return False

def main():
    # Determine which default branch to use
    default_branch = 'main' if branch_exists('main') else 'master'
    if not branch_exists(default_branch):
        print(f"Neither 'main' nor 'master' branch found")
        sys.exit(1)

    print(f"Using {default_branch} as the default branch")

    # Fetch the default branch
    print(f"Fetching {default_branch} branch...")
    run_git_command(['git', 'fetch', 'origin', f'{default_branch}:{default_branch}'])

    # Get current branch name
    current_branch = run_git_command(['git', 'rev-parse', '--abbrev-ref', 'HEAD'])
    print(f"Current branch: {current_branch}")

    if current_branch == default_branch:
        print(f"Already on {default_branch} branch. Nothing to rebase.")
        return

    # Perform the rebase
    print(f"Rebasing {current_branch} onto {default_branch}...")
    try:
        run_git_command(['git', 'rebase', default_branch])
        print("Rebase completed successfully!")
    except:
        print("Rebase encountered conflicts. Please resolve them manually.")
        sys.exit(1)

if __name__ == "__main__":
    main()