Compiling code with Qt5 using CMake on Ubuntu 12.04 - cmake

Question

I have a fairly special setup here and I have not enough knowledge about CMake to find out what is wrong.
I am on Ubuntu 12.04.
I installed Qt5 from apt-add-repository ppa:ubuntu-sdk-team/ppa and CMake 2.8.11.2 from apt-add-repository ppa:kalakris/cmake (https://launchpad.net/~kalakris/+archive/ubuntu/cmake).
Here is the complete, minimal test-case:
daniel#omni-travis-test:~/projects/qtcmaketest$ ls
blubb.cpp CMakeLists.txt
daniel#omni-travis-test:~/projects/qtcmaketest$ cat CMakeLists.txt
cmake_minimum_required(VERSION 2.8.11)
project (qtcmaketest)
find_package (Qt5Widgets REQUIRED)
add_executable(qtcmaketest blubb.cpp)
target_link_libraries (qtcmaketest Qt5::Widgets)
daniel#omni-travis-test:~/projects/qtcmaketest$ cat blubb.cpp
#include <QWidget>
#include <QApplication>
int main (int argc, char * argv[])
{
QApplication app (argc, argv);
QWidget foo;
foo.show ();
}
daniel#omni-travis-test:~/projects/qtcmaketest$ cmake . && make
-- The C compiler identification is GNU 4.8.1
-- The CXX compiler identification is GNU 4.8.1
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/daniel/projects/qtcmaketest
Scanning dependencies of target qtcmaketest
[100%] Building CXX object CMakeFiles/qtcmaketest.dir/blubb.cpp.o
/home/daniel/projects/qtcmaketest/blubb.cpp:1:19: fatal error: QWidget: No such file or directory
#include <QWidget>
^
compilation terminated.
make[2]: *** [CMakeFiles/qtcmaketest.dir/blubb.cpp.o] Error 1
make[1]: *** [CMakeFiles/qtcmaketest.dir/all] Error 2
make: *** [all] Error 2
Why is the include directory missing when find_package was successful?
I was using this guide:
http://qt-project.org/doc/qt-5/cmake-manual.html
I just noticed that, when following the instructions from the chapter "Using Qt 5 with CMake older than 2.8.9", compilation works. I added the following lines:
include_directories(${Qt5Widgets_INCLUDE_DIRS})
add_definitions(${Qt5Widgets_DEFINITIONS})
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS}")
I know that this should work without those lines, since it runs on an Ubuntu 14.04 box (which includes the appropriate Qt and CMake versions by default). I don't expected to get a solution to this problem, but I could need some pointers on where to look for the problem.

Answer 1

I'm pretty sure that the problem lies in the version of Qt. I think that this early Qt 5 version does not include the CMake scripts to properly work with find_package alone.
On newer distros with newer Qt 5, it works as expected. Looks like you have to add special version checks to include or exclude the lines I mentioned as a workaround.
Additional info: Since Ubuntu 12.04 is really old, I decided not to support it as a target build platform for my project.
My initial reason was that Travis CI uses 12.04, but since it is so much trouble, I will hold my travis builds until they upgrade to 14.04, which seems to be quite a problem.
Travis tweeted to me, on December, 12th 2014:
Travis CI: We are working on it. Most pieces are there, but there is a critical issue with infrastructure. Thanks for your patience.

Answer 2

Here I recently had the same problem and found the following solution to install newer Qt5 versions which enables cmake to proceed properly:
sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu trusty universe"
sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu trusty main"
sudo add-apt-repository --yes ppa:kalakris/cmake
sudo apt-get update -qq
sudo apt-get install cmake
sudo apt-get install qdbus qmlscene qt5-default qt5-qmake qtbase5-dev-tools qtchooser qtdeclarative5-dev xbitmaps xterm libqt5svg5-dev qttools5-dev qtscript5-dev qtdeclarative5-folderlistmodel-plugin qtdeclarative5-controls-plugin -y
In the end I ended up using the following .travis.yml file to get things going:
https://github.com/hzdr/qutselect/blob/master/.travis.yml
Hope that also solves your problems.