[berkut]

I think CMake is one of the best (not saying it's perfect) C/C++ build systems I've used (used jam, make, automake, qmake, scons quite comprehensively, either via choice or under duress), and there are some things that are close to impossible (or were a few years ago).

One of these was getting an executable that's built as part of a script to generate a .cpp which is then built as another lib as a further dependency within the same build - I believe that's possible now as OpenEXR does it. Similarly, I've had to run external programs that binary patch executables and had serious issues doing that.

[janoc]

That isn't all that hard to do, CMake routinely supports this for e.g. Swig or Qt's moc/uic/rcc tools. The code generator creates a bunch of files and those can be either built as a library or added to your normal list of sources.