“It submits over 1000 deletion changelists per week, and has so far deleted nearly 5% of all C++ at Google.”
Google logs every run of every internal binary, and anything idle for long enough gets a deletion request. Tests can’t count as proof of life, or every tested library would live forever, so each test shares the fate of the code it tests. Nearly 5% of Google’s C++ was dead weight that CI kept testing and migrations kept porting. The hard part is the engineers who don’t want a robot deleting code they wrote.