[CMake] Converting a large C++-Project to CMake

[Benjamin King]

Hi Karl!


> I'm currently (as a consultant) converting ~2.5 Mio LOC C++/C from
> vcproj/Makefiles/qmake to cmake.

Can you say something of the motivations for  your client to do this?

I suspect that you are expected to keep most of their development 
workflow and processes in order. Which parts are you allowed to redesign 
and which have to stay?

For us, there are also strong non-technical factors that will affect the 
decision to improve the build system, such as:
1) Is there some migration path from the old system?
2) Can we get around taking two weeks off where everybody needs to learn 
a new tool?
3) Can we keep the knowledge that went into the scripts, makefiles and 
qmake-projects of the current system?
4) Does it offer enough advantages to take the risk to change a matured 
and operative build system (albeit the latter is running at its limits)?

There are more points, but I'll need to address them all in order to 
convince anyone to even try cmake.

Right now, my plan is to convert a substantial part of the project to 
cmake. It needs to work with all our code generators. It will include a 
subproject that has a substantial amount of unit, integration and 
regression test that all need to be passed afterwards. And the migration 
path could be to just check in the CMakeLists.txt into the repository 
and be grateful that cmake builds out of source.

Part of my non-technical review will be the amount of time and pain it 
took me to do the conversion. The book (Mastering CMake) and the 
superfriendly and professional mailing lists will surely be big selling 
points there :-)

I'd be really interesting to know what non-technical issues you are 
facing with your current project!


> - Automate everything (You need: continuous build and delivery, use
> cdash or hudson)
> - Complete build process (You need: checkout, build, packaging and install)

We do that with bash scripts and virtual machines.
Which is why running cmake must be fully scriptable.
I understand that it is if you are passing it the required configuration
parameters with cmake -DTHIS_AND_THAT.


> There are others ways to build faster, like ccache
> (http://ccache.samba.org/) or distcc (http://distcc.samba.org/).

We are using both for regular developer builds in linux. With release 
builds, we are a little more reluctant and expect everything to build in 
bearable time from scratch on a single machine. This works, just short 
of the bearable part.


> If you are going to change tools (introduce cmake), it is also time to
> review your development process (If in the business world e.g. a
> SAP-Systems is introduced the complete work flow and business processes
> will get adapted).

I'll collect all the suggestions from this list and summarize them in a 
report.

Thanks a lot for being so helpful, that's much appreciated!


Cheers,
   Benjamin