Heads-up : automoc changes in CMake 3.8

[Christophe Giboudeaux]

Hi,

CMake 3.8 comes with a change that could break compilation under certain 
circumstances.(*)

in CMake < 3.8, automoc'ed files are stored in <CMAKE_CURRENT_BINARY_DIR>.

Starting with CMake 3.8, they're now created in :
<CMAKE_CURRENT_BINARY_DIR>/<TARGETNAME>_autogen/include

What does it change ?

In most cases, nothing. moc files will be re-created.

The situation may be different when you invoke automoc manually and also 
#include the file elsewhere.

Example in plasma-framework :
1/ src/plasmaquick/private/configcategory_p.cpp does:
 #include "private/moc_configcategory_p.cpp"

2/ CMake creates
KF5PlasmaQuick_autogen/include/private/moc_configcategory_p.cpp as expected

3/ autotests/configmodeltest.cpp does: 
#include "plasmaquick/private/configcategory_p.cpp

4/ build fails because private/moc_configcategory_p.cpp cannot be found when 
building the autotests.

The solution :

the new moc files location is exported in the target's INCLUDE_DIRECTORIES 
variable. you then have to add it to the $otherTarget's 
target_include_directories' call

for this example, adding :

target_include_directories(${_testname} PRIVATE "$<BUILD_INTERFACE:
$<TARGET_PROPERTY:KF5PlasmaQuick,INCLUDE_DIRECTORIES>>;")

in autotests/CMakeLists.txt is enough. 
i.e: tell  <other target> to add <original target>'s INCLUDE_DIRECTORIES to 
its -I parameters.

Christophe


(*) https://cmake.org/cmake/help/v3.8/release/3.8.html#other-changes