I once worked on a product and identified an ability to eliminate 100K lines of poorly written, inconsistent tracing code into a robust ~250 line file using AspectJ. Management threw a sh-t fit and thought the risk was untenable.

I think what had happened is somebody had designed the file and everybody else followed suit patching stuff on - the entire codebase for that app was well below average. they had front end devs who didn’t know any JavaScript. In 2016. I lasted 6 months before I nope.png’d the fuck out.

It’s still not the worst application I’ve ever worked on though

For some reason all calls were dog slow. Like minutes for simple pages.

Profiling revealed the class in question - and we were spending all our time in deserializing strings.

Copied the latest version of that class from the FB repo and luckily the interfaces were the same.

Worked for the next two years until we finally deprecated the PHP stuff.

It was a support nightmare, so we built a common library and collapsed the code base by 70%. Each tool was probably in the -8k eslocs range. Thankfully it wasnt c++.