Gemini's Guide to the Bazel Central Registry (BCR)

This guide summarizes the essential workflows and policies for contributing to and maintaining the BCR.

📁 Repository Structure

Each module is organized under the modules/ directory:

• modules/<name>/metadata.json: Module-level info (maintainers, versions, homepage).
• modules/<name>/<version>/:
  • MODULE.bazel: The module's dependency definition.
  • source.json: Source archive URL, integrity (SHA-256), and optional patches or overlay.
  • presubmit.yml: CI configuration (platforms, build/test targets).
  • patches/: .patch files to modify upstream source.
  • overlay/: Files to add or overwrite in the upstream source.

⚖️ Important Policies

• Add-only: The BCR is immutable. Never modify an existing version.
• Registry Fixes: If a fix is registry-only (e.g., fixing compatibility with a new Bazel version), append .bcr.<N> to the version (e.g., 1.2.3 -> 1.2.3.bcr.1).
• Bazel 9 Compatibility: Native rules (like cc_library) are being removed.
  • Add bazel_dep(name = "rules_cc", version = "...") to MODULE.bazel.
  • Use load("@rules_cc//cc:defs.bzl", "cc_library", ...) in BUILD files via patches.
• Overlays: When using overlay/, include bazel_compatibility = [">=7.2.1"] in MODULE.bazel.
• Target Names: C++ modules should ideally expose a target with the same name as the module to allow @module_name syntax.

🛠️ Essential Tools

• //tools:add_module: Interactive scaffolding.
• //tools:update_integrity: SHA-256 automation.
• //tools:bcr_validation: Local CI check.
• //tools:setup_presubmit_repos: Local build reproduction.