GitHub Sorts Your Code Alphabetically — And That May Hide Bugs

Most code review tools — the ones teams use at GitHub, GitLab, and similar sites — show you the changed files in alphabetical order. It feels neutral, like sorting a folder. A team of researchers tested whether it actually is. They mined 330,343 multi-file code-change bundles containing 756,814 individual files, pulled from 182 open-source projects written in five programming languages. Then they asked a simple question: does a file's position in that list predict whether it causes problems later?

It does, though modestly. Files appearing further down the list were more likely to be tied to bug-fixing changes afterward — roughly 57% at position one rising to 62% by position 30. The bigger surprise was about attention. Each additional file in a bundle reduced the odds that a reviewer would leave any comment at all by about 8.7%. So the more files there are, the less any single one gets looked at. Bundle size also mattered in a curve: around ten files seemed safest, while very small and very large bundles both carried higher risk.

The study also found what the authors call an "attention-effectiveness gap." Lots of visible comments on a code change does not guarantee fewer bugs. Reviewers may comment heavily on the easy-to-read first few files and skim the rest. That means the tidy alphabetical list isn't a harmless default — it's a structural choice that shapes who looks at what, and how confident anyone should be that a change was actually checked.

The researchers suggest fixes: order files by how they relate to each other, group files that depend on one another, put the risky ones first, and show per-file indicators of how much review each one received. For you, the takeaways are practical. If you submit code for review, keep changes small and point reviewers at the files that matter most. If you review code, don't trust the default order — dig into the files nobody commented on.