[cmake-developers] cmake automoc breaks kde

[Alexander Neundorf]

On Wednesday 02 November 2011, David Faure wrote:
> On Monday 31 October 2011 21:47:31 Alexander Neundorf wrote:
> > On Monday 31 October 2011, David Faure wrote:
> > > This is a typical (kde) case where the .cpp incudes the .moc, for the
> > > object defined in the .h.
> > 
> > Shouldn't it include moc_kauthactionwatcher.cpp ?
> 
> No, that's for the case where the qobject is in the .cpp file.
> 
> > Is this really a typical case, i.e. is that done in many places ?
> 
> Yes. Just grep for moc includes in kde...
> 
> > I thought the rule is that if there is a include foo.moc, the Q_OBJECT is
> > in the same cpp file.
> 
> No, it's the other way around, in KDE.
> 
> $ grep Q_OBJECT kautosavefile.*
> kautosavefile.h:    Q_OBJECT
> $ grep moc kautosavefile.cpp
> #include "kautosavefile.moc"
> 
> > If it did additionally other things, this was more or less accidentially.
> 
> But it was the way kdesupport/automoc always worked, on purpose, not
> accidentally.
> 
> OK, more precisely: it didn't care what the name of the included moc file
> was, what mattered was, where is Q_OBJECT being used.
> 
> As the kde4automoc.cpp code says: when parsing the .cpp file:
> 
> // If the moc include is of the moc_foo.cpp style we expect the Q_OBJECT
> class // declaration in a header file.
> // If the moc include is of the foo.moc style we need to look for a
> Q_OBJECT // macro in the current source file, if it contains the macro we
> generate the // moc file from the source file, else from the header.
> 
> > The logic which is currently implemented is:
> > 
> > 1. if foo.cpp includes foo.moc, run moc on foo.cpp and generate foo.moc
> 
> That should depend on if foo.cpp actually says Q_OBJECT or not. Otherwise
> this .moc should be created from the header file. Not much point in running
> moc over a .cpp that doesn't define a Q_OBJECT :)
> 
> > 2. run moc on all header files bar.h which contain "Q_OBJECT" and
> > generate moc_bar.cpp from them
> 
> That could be moc_bar.cpp or bar.moc depending on which one is included.
> 
> > (which in detail means:
> > 2.1 for every included moc_xyz.cpp (no matter in which file), search for
> > a corresponsing xyz.h/hxx/hpp file and run moc on it
> > 
> > 2.2 for every bar.cpp file, check whether there is a corresponding
> > bar.h/hpp/hxx file and collect it
> > 
> > 2.3 check for a Q_OBJECT macro in all collected header files and all
> > header files listed explicitely as a source for the target, and run moc
> > on them. If the resulting moc_xyz.cpp file has not been included in any
> > source file, include it in <targetname>_automoc.cpp, which is built as
> > part of the target )
> > 
> > Step 2.2 already involves guessing, which I don't like.
> > Beside that, IMO these are clear rules, which are easy to understand.
> > 
> > With the old behaviour it was actually ambigous:
> > 
> > foo.h:
> > class Foo
> > {
> > 
> >   Q_OBJECT
> > 
> > };
> > 
> > 
> > foo.cpp:
> > 
> > Foo::Foo() {}
> > 
> > #include "foo.moc"
> > #include "moc_foo.cpp"
> > 
> > This would have generated twice the same moc file, I think. IMO this is
> > really confusing.
> 
> Well there is no reason to include both, unless you have Q_OBJECT in the
> .cpp file too :-)
> 
> > Now it is simple: foo.moc from foo.cpp, moc_foo.cpp from foo.h.
> > 
> > If this is really done in many places in KDE, I'll add some workaround,
> > but I think the default behaviour should stay as it is now in cmake git.
> > 
> > How does qmake handle such cases ?
> 
> Checking....
> Indeed qmake expects moc_foo.cpp for the standard case (Q_OBJECT in
> header). This is why kde4automoc was made to support both moc filenames,
> so that it could be compatible with the kde way of doing it (foo.moc) and
> with the qmake way of doing it (moc_foo.cpp).
> 
> Oh well, if you want to stick to that we'll change all of KDE, for the
> benefit of a clearer future indeed... At least it won't be an source
> incompatible change for app developers since they will have to enable
> CMAKE_AUTOMOC to get into this situation. Merely upgrading cmake or KDE
> (even to frameworks 5) won't trigger it. OK not exactly,
> find_package(kde4) will stop working so they will -have- to port to
> CMAKE_AUTOMOC, it will be the only solution available...

Please give the RestoreAutmocKDECompatibility branch on cmake stage a try.
It should work again, but print a warning if a file includes a moc_foo.cpp, 
but no foo.moc, and contains a Q_OBJECT macro.

For Qt5 I'd prefer to not support that anymore.
I.e. moc_foo.cpp -> header, foo.moc -> source file.

Alex