"DiskCleaner: The Opt-In Checker That Once Faked a 61-Error Run"

Build-artifact and cache cleanup, as a checker — and a cautionary tale about what happens when a destructive tool runs at the wrong time.

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DiskCleaner reclaims disk from build artifacts and caches — the .build directories, DerivedData, index caches that pile up across a portfolio of projects. It’s opt-in, excluded from default runs, and the reason it’s opt-in is a lesson worth telling.

The 61-error run that wasn’t

Once, while dogfooding the full suite with --check all, the gate reported 61 errors. Alarming — until I traced it. disk-clean had been included in the run, and it did exactly what it’s supposed to: it wiped .build. The next checker to run was the build checker, which now faced an empty build directory and reported the whole project as failing to compile. Sixty-one errors, all an artifact of a destructive cleanup running mid-gate, ahead of the checkers that needed the build tree it just deleted.

Nothing was actually wrong with the code. The “failure” was a sequencing accident: a tool that removes build state has no business running in the same pass as tools that depend on it.

The lesson, encoded

That incident is why disk-clean is opt-in and why the guidance is explicit: exclude disk-clean when dogfooding a full run. It’s a genuinely useful tool for reclaiming space across many checkouts — just not something you want firing automatically alongside the checkers that assume a built tree exists. The checker still ships; it just refuses to be a default, because a destructive default is a footgun waiting for a hurried --check all.

Try it

quality-gate --check disk-clean          # deliberate, opt-in cleanup

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Source: github.com/jpurnell/quality-gate-swift