Some changes are too big to fit into a effort. A few years ago, I was working on a niche compiler. When the project was first started, the decision was made to

Some changes are too big to fit into a effort. A few years ago, I was working on a niche compiler. When the project was first started, the decision was made to inline everything, greatly simplifying the rest of the compiler [0]. This decision had served us well for the better part of its then 17 year lifetime, but was finally starting to cause issues with compile time and memory usage. One of our senior developers, who was intimately familiar with the project, tried on several occasions to allow for things to not get inlined. However, he kept having to give up as it was a low priority background task, and his branch would diverge from the main branch faster than he could keep his up to date. The solution ended up being a rather simple feature flag. Within a few days, he coded a flag that would enable not-inlinging; and updated our test infastructure to look for regressions on unit tests with the flag enabled. Going forward, developers we responsible for making sure their changes didn't cause regression when the flag was enabled; and everyone was able to slowly chip away at everything the feature broke when they had spare cycles. What would have been a major stop-the-world refactor with our most senior engineers, turned into a slow moving non-issue. [0] Lack of turing completeness was and remains an explicit design goal, so recursion was explicitly forbidden.