[CMake] add_subdirectory inheritance

[irukandji]

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