HotSwap: Bringing hot code reloading to Buck

What this post added

Introduced HotSwap, a feature for Buck that enables hot code reloading for Android development. HotSwap leverages Buck's Exopackage support and Java ClassLoaders to allow engineers to incrementally update code without restarting the entire application, drastically reducing the time to verify bug fixes and improving the overall edit-compile-run cycle. It achieves this by inserting a delegate ClassLoader that can be dropped and repopulated from disk when definitions change, leading to a 90% decrease in verification time for bug fixes in benchmarks.