[CMake] Submitting patches to rely on external libraries for certain platforms

[Brandon J. Van Every]

Matt Rogers wrote:
> Hi,
>
> Would the CMake developers be interested in patches that allows people to use 
> their already installed libraries such as curl, expat, libtar, etc. on 
> certain platforms and fallback to the in-source libraries if they're not 
> installed?
>   

Anyone can already write this kind of code using FindXXX and FIND_* 
commands and then some conditionals.  It is not difficult CMake script 
code to write.  You seem to be saying it should / could be automagical.  
I'm not convinced that's beneficial, however.  When people include the 
entire source of a library in their own build tree, it's because they 
want control over how the thing is built.  For instance, the source code 
may have diverged from standard distributions, may be older, may be 
frozen, may be built with CMake instead of Autoconf and be integrated 
with CTest, etc.  When people don't want that level of control, they 
implement FindXXX and FIND_* commands.  I doubt you can provide patches 
that make FindXXX and FIND_* any better than they currently are, so this 
part of the problem never goes away.  It's code that people have to write. 

> Initially, I think this would be great for unix/linux based platforms that 
> generally come with these libraries already installed or very easily 
> available and then can be extended out into the windows world later (when I 
> have information on how to actually do it?
>   

Unix culture is that everyone uses preinstalled libraries.  That is not 
Windows culture.  Windows people expect everyone else to do it wrong, 
there is no central repository of libraries, DLL Hell is abundant, and 
cautious programmers keep and install all their own versions of stuff.


Cheers,
Brandon Van Every