[CMake] Trouble with libraries on MacOS X

[Thomas Christian Chust]

Hello,

I'm using CMake 2.4.6 on a PowerPC iBook running MacOS X 10.4.8 and I
found some issues with building both shared and static libraries and
with linking to static libraries using CMake.

I have attached a very simple example project to this e-mail that can be
used to demonstrate the problems. If you have a look at the
CMakeLists.txt in the example, you can see that it states that both a
shared and a static library should be built from the same sources plus
an executable should be built and linked against the static version of
the library.

Now if you create a build directory for the project using CMake and run
make in it, both libraries and the executable are built -- but somewhere
in the build process the dynamic library is deleted again, so it is gone
from the output directory when the build finishes!

Of course, as the dynamic library has disappeared, the executable that
is produced is linked against the remaining static library, which is
also what the CMakeLists.txt specifies.

But now, in order to keep both libraries try the following in the build
directory:
  make clean
  make lib_shared
  mkdir tmp
  mv liblib.dylib tmp
  make lib_static
  mv tmp/liblib.dylib .

And then build the executable that is specified to link against the
static version of the library:
  make use

If you check the resulting executable with otool -L, you will see that
it is now dynamically linked against liblib.dylib instead of statically
against liblib.a.

I consider this seriously buggy behaviour. First of all I don't like it
that the build system magically wipes out one of the library targets I
ordered it to create. But the more serious problem is the linkage issue:
As CMake tries to be clever and converts any absolute path to a library
passed to TARGET_LINK_LIBRARIES into a combination of -L and -l flags
for the linker, it is completely impossible to link against a static
library on MacOS X if a dynamic library of the same name exists anywhere
on the library search path! The MacOS X linker always prefers dynamic
libraries over static ones if it can find them anywhere.

Is there any portable workaround for this problem? Of course I can
always manually handle the linker flags correctly, but that's tedious
and exactly the type of thing I want to avoid by using CMake.

cu,
Thomas Chust
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