So we have this huge (is 11000 lines huge?) mainmodule.cpp source file in our project and every time I have to touch it I cringe.

As this file is so central and large, it keeps accumulating more and more code and I can't think of a good way to make it actually start to shrink.

The file is used and actively changed in several (> 10) maintenance versions of our product and so it is really hard to refactor it. If I were to "simply" split it up, say for a start, into 3 files, then merging back changes from maintenance versions will become a nightmare. And also if you split up a file with such a long and rich history, tracking and checking old changes in the SCC history suddenly becomes a lot harder.

The file basically contains the "main class" (main internal work dispatching and coordination) of our program, so every time a feature is added, it also affects this file and every time it grows. :-(

What would you do in this situation? Any ideas on how to move new features to a separate source file without messing up the SCC workflow?