Ryzom

The default value of CMAKE_FIND_LIBRARY_SUFFIXES on Mac OS X is ".dylib;.so;.a". So it prefers .dylib over .so over .a.

For some libraries, the system might not provide static ones (e.g. Apple provided libz, libSystem, etc.).
Having a list of extensions enables a fall back solution, while just setting it to one of the extensions will simply fail if the desired one is not available.
WITH_STATIC_EXTERNAL could set CMAKE_FIND_LIBRARY_SUFFIXES to something like .a;.dylib;.so on Mac OS X.

Maybe a similar way could be interesting for Linux based systems as well?

As suggested by rti, I updated code to check for :

• Mac OS X : .dylib .so .a if WITH_STATIC_EXTERNAL is OFF
• Mac OS X : .a .dylib .so if WITH_STATIC_EXTERNAL is ON
• Linux : .so .a if WITH_STATIC_EXTERNAL is OFF
• Linux : .a .so if WITH_STATIC_EXTERNAL is ON

The problem we had recently while compiling a full static client is that libGL.a doesn't exist because it's provided by graphics card drivers, it could exist other cases as for OpenAL which doesn't provide a static library under Ubuntu last version.