[CMake] Forcibly run 'moc' on Qt files that are NOT part of the build

[Michael Jackson]

On Mar 7, 2012, at 11:43 AM, Andreas Pakulat wrote:

> On 07.03.12 10:10:27, Michael Jackson wrote:
>> In an effort to speed up the build of a project that uses Qt (and moc) I tried an alternate approach with the moc files. Normally I use the basic idea of gathering the headers that need to be "moc'ed" and feed those to moc with this type of CMake Code:
>> 
>> QT4_WRAP_CPP( FilterWidgets_Generated_MOC_SRCS ${QFilterWidget_HDRS} ${FilterWidget_GEN_HDRS}) 
>> 
>> The in the Add_Executable(...) call include the ${FilterWidgets_Generated_MOC_SRCS} variable to the list of sources. In my project I have at least 30 auto-generated files which all get moc'ed. That gives me an additional 60 compiled files. So I tried the idea of #include "moc_[some_file.cxx]" in each of the auto-generated .cpp files for each Widget. This would cut the number of files compiled in half. The issue is that since they are being #include'ed in the .cpp files then they do NOT need to be compiled themselves so I took the ${FilterWidgets_Generated_MOC_SRCS} out of the list of sources in the add_executable() call. What happened is that CMake did NOT run moc on those headers because there were now NOT included in the build.
>> 
>> So for that version of the cmake code I have something like this:
>> 
>> QT4_WRAP_CPP( FilterWidgets_Generated_MOC_SRCS ${FilterWidget_GEN_HDRS}) 
>> QT4_WRAP_CPP( FilterWidgets_MOC_SRCS ${QFilterWidget_HDRS} )
>> 
>> Is there a way to forcibly run the moc step even if the resulting source files are NOT directly included in the add_executable? Custom_Command? Add_Depends?
> 
> A few options I can think of:
> 
> - Use the automoc developed as part of KDE (its pure-Qt though)
>    https://projects.kde.org/projects/kdesupport/automoc/repository
> - Use the automoc function from FindQt4.cmake
> - Use the new automoc function in CMake 2.8.7
> 
> All of these will help handle the qt4_wrap_cpp stuff for you as long as
> you have the #include. Note that I think there's at least 2 or 3
> differnet filenames for the include depending on which of the above you
> use (foo.moc vs moc_foo.cpp vs. moc_foo.cxx or something like that).
> 
> If none of them is an option for you then I guess using
> add_custom_target and add_dependencies is the way to go.
> 
> Andreas
> 
I looked into the automoc functionality and after some tinkering around I think there is still a disconnect in my cmake code. When are the source/header files scanned by automoc to determine if they will have moc run on them.
   Currently during cmake time I generate a blank header and source file (well, there is a #error ... in them) which then get over written by a new files during build time. The new files are complete and proper C++ source files/headers with the Q_OBJECT macro in the header and #include "moc_*.cpp" in the source file. When I compile (using makefiles on OS X currently as a test) I get an error that the moc_*.cpp file can not be found and searching the entire build directory does not reveal the file. If I run CMake again and compile then the auto moc files do appear. From this I think that automoc runs during CMake time. Is this correct? 
--
Mike J.