@github: A pull request with 2,200 files, 1M+ changed lines, and 400+ inline comments. Impossible to review? Not if you have the…

A pull request with 2,200 files, 1M+ changed lines, and 400+ inline comments.

Impossible to review? Not if you have the GitHub Copilot app. ✨

The rebuilt pull request view keeps even this extreme diff fast and smooth. 🧵

Code is the easy part: virtualize the rows, keep the DOM small, and use known line heights.

Comments are harder. Their height changes with markdown, replies, expandable sections, images, and async content.

The solution was two independent geometries:

• Deterministic code height, known up front • Dynamic comment blocks, measured lazily and corrected near the viewport

That keeps comment reflows from rebuilding the code layout.

The team also built a measurement loop that ran unattended against a huge pull request, using production instrumentation to detect blank gaps, jank, leaked observers, and scroll corrections.

Check out the deep dive on making million-line pull requests with hundreds of comments feel like ordinary reviews. 👇

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