[cmake-developers] Best practice for determining if a static library was found and other issues with FindFLTK.cmake

[Brad King]

On 09/03/2014 09:48 AM, Richard Shaw wrote:
> The module has several issues but a major one is that it doesn't add
> the required linker flags when using static libraries instead of shared.
> 
> It also doesn't check for any required C flags but that's a lesser issue.
> 
> These may only be a problem for the autotools based fltk build
> as the module uses a ConfigFLTK for CMake based builds.

If FLTK upstream is willing to provide FTLKConfig for CMake-based
builds then they may be willing to support providing one from
autotools-based builds too.  It is not very hard to provide one
from a non-CMake build system.  Qt5 and LLVM both do it.  You
could go work with the FLTK devs to do it there too.  Then we
won't even need a FindFLTK in CMake except for compatibility.

> ^^^ Is this the best way to determine if the library found was
> static or shared? ^^^

It is not possible in general without platform-specific knowledge.
On AIX even an archive (.a) can be a shared library, for example.
On Windows a .dll's import library (.lib) looks just like a static
library (.lib).  Ideally information provided with the FLTK package
should tell us.

> So a broader question... Should we trust the output of a config
> program, in this case, fltk-config? The writer of the module
> certainly doesn't. They used the fltk-config program to find
> the base library, strip off the path portion and then used it
> as a search path to find the libraries independently. 

Of course the output of fltk-config should be trusted to be
correct, but the info still needs to be transformed into what
CMake wants.  That is usually more granular than strings of
command-line flags for various tools, so some parsing/searching
may be needed.

> I would like to update the module to use COMPONENTS, but the
> current default is to find everything unless a "FLTK_SKIP_..."
> variable is set so I assume there's a good way to keep
> backward compatibility. 

The FindFLTK module was added way back in the beginning of CMake
and has never really been modernized.  The SKIP variables may
even predate the COMPONENTS support in find_package.

-Brad