Commit 321e348e (QtAutogen: Use Qt 4 IMPORTED targets to find
executable locations., 2014-01-24) attempted to fix this problem,
but only solved it for a particular ordering of find_package for
Qt 4 and Qt 5.
Add a test to ensure that it works with both orderings.
Avoid using the moc from Qt 5 with Qt 4 based targets. Moc generates
a version check to ensure that such generated code does not compile.
The Qt4And5Automoc unit test should have been testing this, but it
was not because the test was broken. In that unit test, moc was run
on trivial files which have no significant content, and in particular
no Q_OBJECT macro. Therefore moc was generating empty files which
do not even contain the version check. Fix this by generating files
for input to moc at cmake time.
In Qt 5.1, Qt5::Core has a INTERFACE_QT_MAJOR_VERSION property
of '5', and since CMake 2.8.11, Qt4::QtCore has an
INTERFACE_QT_MAJOR_VERSION of '4'. This was introduced in
commit 4aa10cd6 (FindQt4: Set the INTERFACE_QT_MAJOR_VERSION for
Qt4::QtCore, 2013-03-16), to produce an error if Qt 4 and Qt 5
are erroneously used by the same target. This can also be used
however to determine the Qt major version, and therefore the
particular moc executable to use during automoc steps. This means
that targets in a single buildsystem can use a selection of Qt 4
and Qt 5, and still take advantage of the CMAKE_AUTOMOC feature
without conflicting.
