[CMake] Correct handling of absolute/relative installation paths

[David Demelier]

Le 27/07/2017 à 13:08, Eric Noulard a écrit :
> 
> 
> 2017-07-27 12:28 GMT+02:00 David Demelier <demelier.david at gmail.com 
> <mailto:demelier.david at gmail.com>>:
> 
>     Hello,
> 
>     I'm still trying to find a correct solution to handle user specified
>     installation paths.
> 
>     Let's consider two kind of paths:
> 
>        - WITH_BINDIR (default: bin/) where to install executables,
>        - WITH_DATADIR (default: share/project_name/) where to install
>     extra data.
> 
>     I want to let the user configuring those paths because not all
>     distributions use the same paths (e.g. bin vs usr/bin).
> 
>     Then, I also like to build the whole CMake project by creating the
>     hierarchy as it would be installed like:
> 
>     <binarydir>/WITH_BINDIR/myapp
>     <binarydir>/WITH_DATADIR/somestuff.txt
> 
> 
> Do you mean here that you setup CMAKE_<XXXX>_OUTPUT_DIRECTORY (variable 
> or target property) to your favorite value
> or
> 
Both, I set the output directory for executable to WITH_BINDIR value and 
also install it as destination.

> My opinion is that you should never use absolute path (besides some very 
> specific case on unix where you want to put something in /etc/...)
> You should ask your user for
> 
>     DATADIR
>     BINDIR
>     etc...
> 

This is what I have done in my CMakeLists.txt, the cmake invocation 
fails if BINDIR and/or DATADIR are absolute. But again, then with some 
package managers you get in troubles because they specify absolute path.

See the RPM default macro:

   /usr/bin/cmake \
         -DCMAKE_C_FLAGS_RELEASE:STRING="-DNDEBUG" \
         -DCMAKE_CXX_FLAGS_RELEASE:STRING="-DNDEBUG" \
         -DCMAKE_Fortran_FLAGS_RELEASE:STRING="-DNDEBUG" \
         -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
         -DCMAKE_INSTALL_PREFIX:PATH=/usr \
         -DINCLUDE_INSTALL_DIR:PATH=/usr/include \
         -DLIB_INSTALL_DIR:PATH=/usr/lib64 \
         -DSYSCONF_INSTALL_DIR:PATH=/etc \
         -DSHARE_INSTALL_PREFIX:PATH=/usr/share \

And if you add any new variable, you should prefix by %{prefix} which is 
also absolute...

> I wouldn't try to mimic install tree during the build (if it is what you 
> are doing),

The nice thing is that you can easily run/debug the application 
especially if that application needs to find some plugins/data while 
running by evaluating paths to them.

I'll probably go for something like a pre-install target like you said 
instead of mimic'ing the build tree. And disable that target if any of 
the paths are absolute.

Thanks for the answers!