[CMake] add_subdirectory inheritance

[Kent Williams]

I think then that you shouldn't use add_subdirectory.

I'd suggest using the ExternalProject module in this case, because it
uncouples the subdirectory's project from the parent project.  In that
case, each subdirectory can be its own project and maintain private
configurations.

You can manage dependencies between ExternalProjects with the DEPENDS keyword.

I think that what you're describing doesn't really make any sense to
me.  I don't know how you'd ever maintain a sane overall project if it
depends on each subdirectory having conflicting compiler flags.

Another way you can manage this sort of thing is to use Source file
properties -- see SET_SOURCE_FILE_PROPERTIES in the CMake
documentation and the "Properties on Source Files" section as well.


On Tue, Apr 17, 2012 at 1:27 PM, irukandji <irukandji at voidptr.eu> wrote:
> Oh, hi :)
>
> Well, the add_subdirectory takes all the preprocessor defines and
> include/library
> paths defined before calling it into the added "subdirectory"
> cmakelists.txt.
>
> If cmakelists.txt A defines -DWhatever and calls add_subdirectory(/B) where
> the
> cmakelists.txt for building library B resides then the library B is going to
> be
> built with -DWhatever. This is probably great behaviour for some cases but
> can
> also be undesired:
> in my case, each library has its own description file, residing in same
> directory
> as its cmakelists.txt, with only one function, which is included and called
> with few
> parameters to specify runtime etc. by each binary which has a dependancy to
> library.
> The description file function sets the -I to itself for caller, the -l to
> its output
> and, if the output file is not found, also calls add_subdirectory on its own
> directory.
>
> This is a perfect situation for developers as we can just do out of source
> configuration
> for whatever directory (where project resides) and only the dependancy tree
> for that
> particular binary is built.
>
> It also brings additional benefit that the team which takes care about
> specific
> library also takes care for description file and needed defines which splits
> the
> ownership of projects and also presents a single point of inclusion for that
> particular
> library, meaning only one file has to be changed for library
> specializations.
>
> For the nightly builds, only executables are added to the build while
> everything
> else is built only if actually used.
>
> It works great, but the add_subdirectory is propagating the settings from
> executable
> to dependant libraries and messes the build.
>
> The question actually is: can i workaround this behaviour and if not, can
> you please
> include the parameter to add_subdirectory function to NOT propagate the
> settings.
>
> Regards,
> Irukandji
>
>
> On 2012-04-17 17:58, Kent Williams wrote:
>>
>> Frankly, I don't entirely understand what the problem is, or what your
>> proposed solution is.
>>
>> What is it that you don't want the subdirectory context to inherit?
>>
>> On Tue, Apr 17, 2012 at 10:30 AM, irukandji <irukandji at voidptr.eu> wrote:
>>>
>>> Hi,
>>>
>>> (as no one answered to my previous email, let me add this: multiplatform
>>> project with few million lines
>>> of code, sheer size of the project is not allowing to turn around whole
>>> directory tree as price / performance
>>> is a very relevant factor and even rewriting makefiles/vcprojs to cmake
>>> will
>>> take months)
>>>
>>> The add_subdirectory inheritance striked which is practically a show
>>> stopper, it was already discussed here
>>> http://www.mail-archive.com/cmake@cmake.org/msg34291.html What was
>>> proposed
>>> (DONT_INHERIT) was a great idea
>>> and improvement to versability of CMake and also harmless for backward
>>> compatibility so i dont really
>>> understand why forcing subproject to inherit all the settings.
>>>
>>> Yes, what is added with add_subdirectory is not a child but a sibling or
>>> even some other part of the tree
>>> but the point is that it doesnt stop the cmake from building it correctly
>>> but this inheritance is a problem
>>> as it adds include directories to wrong versions of headers in public
>>> libs
>>> (due to bugs in different versions,
>>> affecting different platforms,... the unification is impossible), the
>>> flags
>>> are used on wrong places etc.
>>>
>>> Is there a way to workaround it?
>>>
>>> Thank you.
>>>
>>> --
>>>
>>> Powered by www.kitware.com
>>>
>>> Visit other Kitware open-source projects at
>>> http://www.kitware.com/opensource/opensource.html
>>>
>>> Please keep messages on-topic and check the CMake FAQ at:
>>> http://www.cmake.org/Wiki/CMake_FAQ
>>>
>>> Follow this link to subscribe/unsubscribe:
>>> http://www.cmake.org/mailman/listinfo/cmake
>
>
> --
>
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the CMake FAQ at:
> http://www.cmake.org/Wiki/CMake_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.cmake.org/mailman/listinfo/cmake