Mastering Chained CLs in the Chromium Workflow

What this episode covers

In Chromium development, chained change lists (CLs) allow engineers to decompose massive features into a stack of smaller, dependent commits for easier code review. This workflow utilizes depot_tools, a suite of specialized Git wrappers, to manage these relationships through commands like git new-branch and git rebase-update. While each CL in the chain is reviewed as a separate entity in Gerrit, the tools ensure they remain linked so that the Commit Queue (CQ) can test and submit them in the correct sequence. Developers must carefully manage these stacks by rebasing child branches whenever a parent is updated to maintain a clean diff and prevent build breakages. The system also supports cross-repository dependencies by using shared Gerrit topics or specific Cq-Depend footers to coordinate changes across multiple sub-projects. Ultimately, this approach promotes a modular review process while providing the automation necessary to keep complex, multi-part changes synchronized with the main codebase.

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