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Google copybara: moving code between repositories

Google has open-sourced Copybara, an internal tool designed to transform and move code between various repositories. This utility addresses the complex challenge of synchronizing codebases, such as maintaining public and private versions of a project. Its release is notable for providing a battle-tested solution from Google for sophisticated code management scenarios.

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The Lowdown

Copybara is an internal tool developed and used by Google, now made publicly available, that facilitates the transformation and movement of code between different repositories. It's designed for scenarios where source code needs to exist in multiple places, ensuring synchronization and consistency across them.

  • Core Functionality: Copybara's primary role is to move and transform code, allowing for the maintenance of various repositories in sync, often balancing confidential and public versions of a project.
  • Authoritative Source: The tool mandates the designation of one repository as the authoritative source, ensuring a single source of truth while still permitting contributions to any linked repository.
  • Use Cases: Common applications include importing sections of code between confidential and public repositories, and seamlessly integrating changes made in non-authoritative repositories back into the authoritative one.
  • Technical Design: It operates in a stateless manner, with its state embedded as labels within the destination repository's commit messages, promoting consistent results across multiple users or services.
  • Repository Support: Currently, it officially supports Git repositories, with experimental support for Mercurial, and boasts an extensible architecture for future integrations.
  • Getting Started: Users can begin with weekly snapshot releases, build the tool from source using Bazel and JDK 11, or utilize system packages and Docker for deployment and execution.

This robust solution offers developers a powerful mechanism to manage intricate code synchronicity challenges, reflecting Google's operational practices in large-scale software development.