[CMake] order of includes seems wrong (or please help me understand)

[Mario Emmenlauer]

Should I report this as a bug or am I just doing something wrong?
Help would be greatly appreciated!

All the best,

    Mario


On 26.07.2018 11:58, Mario Emmenlauer wrote:
> 
> Dear CMake users and developers,
> 
> I've just discovered a build problem that comes from a wrong order of
> includes. I would know the correct order, but I am unable to instruct
> CMake to use the order I need.
> 
> Here is a toy example that I tested with cmake 3.12.0:
> 
> 
> ----
> cmake_minimum_required(VERSION 3.8)
> project(MyLib VERSION 1.0.0)
> find_package(XXX REQUIRED)
> find_package(YYY REQUIRED)
> add_library(${PROJECT_NAME} include/MyLib.hh src/MyLib.cc)
> target_include_directories(${PROJECT_NAME}
>     PRIVATE
>         ${CMAKE_CURRENT_SOURCE_DIR}/src
>         ${CMAKE_CURRENT_BINARY_DIR}
>     PUBLIC
>         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
>         $<INSTALL_INTERFACE:include>
>         ${XXX_INCLUDE_DIRS} ${YYY_INCLUDE_DIRS})
> target_link_libraries(MyLib PUBLIC ${XXX_LIBRARIES} ${YYY_LIBRARIES})
> # here come more commands for build flags etc.
> 
> enable_testing()
> add_executable(MyTest test/src/MyTest.cc test/src/MyTest.hh)
> target_include_directories(MyTest PRIVATE
>     ${CMAKE_CURRENT_SOURCE_DIR}/include
>     ${CMAKE_CURRENT_SOURCE_DIR}/test/src
>     ${CMAKE_CURRENT_SOURCE_DIR}/src
>     ${CMAKE_CURRENT_BINARY_DIR}
>     ${GTEST_INCLUDE_DIRS})
> target_link_libraries(MyTest PRIVATE MyLib ${GTEST_MAIN_LIBRARIES})
> # here come more commands for build flags etc.
> ----
> 
> 
> I configure cmake with -DCMAKE_PREFIX_PATH=${MY_PREFIX_PATH}. When
> I build the project, the order of includes for MyLib is fine. But
> for MyTest, the following are the first two includes:
>    -IMyTest_autogen/include
>    -I${MY_PREFIX_PATH}/include
> 
> I think the second include should come much later, only *after*
> ${CMAKE_CURRENT_SOURCE_DIR}/include, but it comes before. Therefore,
> if older headers exists in ${MY_PREFIX_PATH}/include, they will be
> used instead of ${CMAKE_CURRENT_SOURCE_DIR}/include!
> 
> I found that I can fix the problem by adding 'BEFORE' to all
> target_include_directories(). However I'm puzzled why this helps.
> Before anything I call target_include_directories(), and before other
> includes I have ${CMAKE_CURRENT_SOURCE_DIR}/src,
> ${CMAKE_CURRENT_BINARY_DIR} and ${CMAKE_CURRENT_SOURCE_DIR}/include.
> So what does 'BEFORE' mean in this case? Aren't these the first
> includes any ways?
> 
> Thanks for any help, and Cheers,
> 
>     Mario Emmenlauer



Viele Gruesse,

    Mario Emmenlauer


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