[CMake] Removing duplicate entries from CXXFLAGS

[Attila Krasznahorkay]

Hi Roman,

I'm not necessarily only talking about CMAKE_CXX_FLAGS here. I define compile flags for my targets in a number of different ways. Like:

   find_package( ROOT COMPONENTS ${ROOT_LINK_COMPONENTS} REQUIRED )
   include( ${ROOT_USE_FILE} )
...
   add_definitions( ${ATLAS_DEFINITIONS} )
...
   add_definitions( -Wno-unused-local-typedefs )
   if( APPLE )
      add_definitions( -Wno-tautological-undefined-compare )
      add_definitions( -Wno-inconsistent-missing-override )
   endif()
...
   include_directories( BEFORE ${CMAKE_CURRENT_SOURCE_DIR}
      ${CMAKE_INCLUDE_OUTPUT_DIRECTORY} )
   if( ARG_INCLUDE_DIRS )
      target_include_directories( ${libName} PUBLIC ${ARG_INCLUDE_DIRS} )
   endif()

The trickiest are the definitions that I pull in from external packages. For instance the second line in this example produces a *lot* of duplicate entries in the compilation flags. In this particular case the flags *are* defined like the following in the file that I include with ${ROOT_USE_FILE}:

add_definitions(${ROOT_DEFINITIONS})
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ROOT_CXX_FLAGS}")

Now, CMake definitely doesn't remove the duplicates that enter in all these ways. So now I was wondering what I could do to improve on the situation...

Cheers,
           Attila

> On 06 Oct 2015, at 12:58, Roman Bolshakov <roolebo at gmail.com> wrote:
> 
> CMake performs deduplication of per-target flags for sure.
> 
> However I'm not sure if CMAKE_CXX_FLAGS is deduplicated. But I consider this variable as global flags for the whole project which is defined at topmost CMakeLists.txt. If you need to specify some flags specifically for a target use target_compile_options.
> 
> —
> Sent from Mailbox
> 
> 
> On Mon, Oct 5, 2015 at 4:23 PM, Attila Krasznahorkay <attila.krasznahorkay at gmail.com> wrote:
> 
> Dear All, 
> 
> Let me try a simpler question this time. (I'm a bit disappointed that nobody had any comments on my question about sub-projects.) 
> 
> I'm trying to clean up my project's build a bit. As it collects compilation flags from a few separate places, by the time it finishes collecting everything, the compilation commands are usually very long. As they have many duplications. Like: 
> 
> -m64 -pipe -W 
> -Wall -Woverloaded-virtual -fsigned-char -fno-common -Qunused-arguments -pthread -std=c++11 -Wno-deprecated-declaration 
> s -stdlib=libc++ -m64 -pipe -W -Wall -Woverloaded-virtual -fsigned-char -fno-common -Qunused-arguments -pthread -std=c++ 
> 11 -Wno-deprecated-declarations -stdlib=libc++ -Wno-unused-local-typedefs -Wno-tautological-undefined-compare -Wno-incon 
> sistent-missing-override -m64 -pipe -W -Wall -Woverloaded-virtual -fsigned-char -fno-common -Qunused-arguments -pthread 
> -std=c++11 -Wno-deprecated-declarations -stdlib=libc++ -m64 -pipe -W -Wall -Woverloaded-virtual -fsigned-char -fno-commo 
> n -Qunused-arguments -pthread -std=c++11 -Wno-deprecated-declarations -stdlib=libc++ -m64 -pipe -W -Wall -Woverloaded-vi 
> rtual -fsigned-char -fno-common -Qunused-arguments -pthread -std=c++11 -Wno-deprecated-declarations -stdlib=libc++ -m64 
> -pipe -W -Wall -Woverloaded-virtual -fsigned-char -fno-common -Qunused-arguments -pthread -std=c++11 -Wno-deprecated-dec 
> larations -stdlib=libc++ -m64 -pipe -fsigned-char -fno-common -Qunused-arguments -pthread -std=c++11 -stdlib=libc++ 
> 
> Naturally it would help the build log reading tremendously if I could remove the duplications from these lines. But I can't find a good way of doing it. How could I weed out all the duplications in the CXXFLAGS associated to a given target? 
> 
> Cheers, 
> Attila 
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