[CMake] order of include dirs

[Brad King]

Alexander Neundorf wrote:
>>Von: Brad King <brad.king at kitware.com> 
>> 
>>Alexander Neundorf wrote: 
>>
>>>in KDE we have the problem that e.g. when compiling kdebase the 
>>>headers  
>>>in the source dir should be preferred over the installed ones.  
>>>Usually we would do   
>>>include_directories( ${KDE4_INCLUDES} ) in the toplevel 
>>>CMakeLists.txt.  
>>>When adding more include dirs in CMakeLists.txt in deeper 
>>>directories, these directories will be appended to the list of 
>>>include dirs, except when used with the BEFORE keyword.  
>>>But now we cannot realistically expect that every KDE developer will  
>>>always remember the BEFORE keyword.  
>>>So we had two ideas:  
>>>make the behaviour configurable:  
>>># make prepend default:  
>>>set(CMAKE_INCLUDE_DIRS_APPEND false)   
>>># to force appending:  
>>>include_directories(AFTER dir1 dir2)  
>>>  
>>>Problem here: moving cmake files around to another project where this  
>>>isn't set would change the behaviour.  
>>>  
>>>Second idea:  
>>>  
>>>include_directories(LAST dir1 dir2)  
>>>  
>>>which would have the effect that the listed directories would always 
>>>be used after all other include dirs specified without the "LAST" 
>>>keyword.  
>>
>> 
>>I think that will create two ordered lists of include directories 
>>instead of one, which will just be confusing.   
> 
>  
> What about the first idea ? 
> I think this would fit good to the include_directories() command. 

I think a magic switch that can easily be accidentally inherited by 
projects not expecting it will not work well.  Eventually we plan to 
make include directories a target-specific setting.  At that point we 
will design a better default ordering.

-Brad