[janislaw]

Can anybody explain the existence of all*.cpp files which include other source files?

[Jare]

That's called a "unity build". https://en.wikipedia.org/wiki/Unity_build

[JTyQZSnP3cQGa8B]

I guess it's a way to optimize the build somehow, but you can achieve the same result with a proper build system, well-defined targets, and precompiled headers, but it's more work for the developers.