[CMake] Include-Dir order problem

[Michael Hertling]

On 02/15/2011 07:36 PM, Andreas Pakulat wrote:
> On 15.02.11 17:54:29, Michael Hertling wrote:
>> On 02/13/2011 01:27 AM, Andreas Pakulat wrote:
>>> Hi,
>>>
>>> I've got a somewhat tricky problem here with include directories. I'm
>>> building a couple of source files and for some of them I need to add an
>>> include-directory to the front of the list that cmake passes to the
>>> compiler. At the same time other source files in that directory need to
>>> not have that include-dir in front of the list.
>>>
>>> I can't see a way to do this, except by using COMPILE_FLAGS source file
>>> properties for each and every file to specify include-dirs and not use
>>> include_directories at all, as COMPILE_FLAGS always end up behind the
>>> includes.
>>>
>>> So, am I missing something here? If not I guess I'll have to find that
>>> bugreport about making include-dirs a source-file property and vote for
>>> it so it gets included into 2.8.5...
>>
>> Currently, AFAIK, it's not possible to set source-file-specific include
>> directories unless one (mis)uses COMPILE_FLAGS which is accompanied by
>> the shortcoming you've mentioned. Probably, the really clean solution
>> ATM would be a reorganisation of the sources, but I doubt if the need
>> for different include directories is an appropriate criterion for a
>> project's directory layout.
> 
> Well, all those sources need to be in the same target, so I can't quite
> see how moving some of the sources into subdirs wuld help with that.

Look at the following CMakeLists.txt files:

# CMakeLists.txt:
CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
PROJECT(INCLUDEDIRECTORIES C)
ADD_SUBDIRECTORY(subdir)
INCLUDE_DIRECTORIES(abc)
FILE(WRITE ${CMAKE_BINARY_DIR}/main.c "int main(void){f();return 0;}\n")
ADD_EXECUTABLE(main main.c)
TARGET_LINK_LIBRARIES(main sub)

# subdir/CMakeLists.txt:
INCLUDE_DIRECTORIES(xyz)
FILE(WRITE ${CMAKE_CURRENT_BINARY_DIR}/f.c "void f(void){}\n")
ADD_LIBRARY(sub STATIC f.c)

So, main.c and f.c are compiled with different include directories, but
the "main" target is effectively composed from the same object files as
if f.c had been explicitly mentioned among the source files for "main".
If you commute the ADD_SUBDIRECTORY() and INCLUDE_DIRECTORIES() commands
in the top-level CMakeLists.txt, the include directories for main.c will
also hold for f.c while the latter still has its own - additional - ones.

Things become worse if the target to be built is a shared library. Most
probably, you don't want an additional libsub.so, so you would need to
compile f.c at least with "-fPIC" as COMPILE_FLAGS to get further along
with a static library. Alternatively, you might use a RULE_LAUNCH_LINK
property in order to capture the object files from the subdirectory and
incorporate them in the actual target, see [1]. However, then you would
be restricted to a Makefile generator. IMO, none of these appoaches is
really convincing why one should aim at an INCLUDE_DIRECTORIES source
file and target property.

Regards,

Michael

[1] http://www.mail-archive.com/cmake@cmake.org/msg34148.html