CMAKE_LIBRARY_PATH & co.

CMAKE_LIBRARY_PATH & co.

[Ludovic Courtès]

Andreas Enge <andreas@enge.fr> skribis:

> commit e78fd4ca636a19bc286747f8d91bda22cd8f08fd
> Author: Andreas Enge <andreas@enge.fr>
> Date:   Sun Oct 13 18:02:49 2013 +0200
>
>     guix: Make cmake build system aware of usual paths.
>     
>     *  guix/build/cmake-build-system.scm (configure): Set CMAKE_LIBRARY_PATH to
>          LIBRARY_PATH and CMAKE_INCLUDE_PATH to CPATH.

I think this was discussed on IRC yesterday, but I’m not sure I got it:
are these needed because CMake explicitly looks for files in these
directories instead of just running the compiler?

That would be a serious flaw of CMake.

Thanks,
Ludo’.

Re: CMAKE_LIBRARY_PATH & co.

[Lluís Batlle i Rossell]

On Mon, Oct 14, 2013 at 09:15:25AM +0200, Ludovic Courtès wrote:
> Andreas Enge <andreas@enge.fr> skribis:
> 
> > commit e78fd4ca636a19bc286747f8d91bda22cd8f08fd
> > Author: Andreas Enge <andreas@enge.fr>
> > Date:   Sun Oct 13 18:02:49 2013 +0200
> >
> >     guix: Make cmake build system aware of usual paths.
> >     
> >     *  guix/build/cmake-build-system.scm (configure): Set CMAKE_LIBRARY_PATH to
> >          LIBRARY_PATH and CMAKE_INCLUDE_PATH to CPATH.
> 
> I think this was discussed on IRC yesterday, but I’m not sure I got it:
> are these needed because CMake explicitly looks for files in these
> directories instead of just running the compiler?
> 
> That would be a serious flaw of CMake.

Right; for what I understand, FIND_LIBRARY, and FIND_PATH, look for files in
specific directories. Then cmake takes a decision based in what it finds. A
shared object, a static lib, ...

For header files, you can do:
FIND_PATH(HEADERS file.h)  # Finds the directory having that file
INCLUDE_DIRECTORIES(${HEADERS})  # Adds the respective -I flag in compilation

It may be related to cmake being able to tune very narrowly the -I/-L flags per
project target.

I'm not that anti-cmake; I find the approach of "look for files" quite easy to
understand. :)

Re: CMAKE_LIBRARY_PATH & co.

[Ludovic Courtès]

Lluís Batlle i Rossell <viric@viric.name> skribis:

> On Mon, Oct 14, 2013 at 09:15:25AM +0200, Ludovic Courtès wrote:
>> Andreas Enge <andreas@enge.fr> skribis:
>> 
>> > commit e78fd4ca636a19bc286747f8d91bda22cd8f08fd
>> > Author: Andreas Enge <andreas@enge.fr>
>> > Date:   Sun Oct 13 18:02:49 2013 +0200
>> >
>> >     guix: Make cmake build system aware of usual paths.
>> >     
>> >     *  guix/build/cmake-build-system.scm (configure): Set CMAKE_LIBRARY_PATH to
>> >          LIBRARY_PATH and CMAKE_INCLUDE_PATH to CPATH.
>> 
>> I think this was discussed on IRC yesterday, but I’m not sure I got it:
>> are these needed because CMake explicitly looks for files in these
>> directories instead of just running the compiler?
>> 
>> That would be a serious flaw of CMake.
>
> Right; for what I understand, FIND_LIBRARY, and FIND_PATH, look for files in
> specific directories. Then cmake takes a decision based in what it finds. A
> shared object, a static lib, ...

Blech.

That’s flawed because CMake’s auto-configuration rules behave
differently from what the compiler/linker actually do.  So its
configuration phase may end up making decisions based on erroneous
information.

Thanks for the explanations,
Ludo’.