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

[Michael Wild]

On 03/07/2012 04:10 PM, 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?
> 
> Thanks

You could still add them to the add_executable() call, but set their
HEADER_FILE_ONLY source file property to TRUE to prevent them from being
compiled. This way they would still show up in the proper place in
IDE's, and no need for fiddling around with add_custom_target() and
add_dependencies(). Of course, you might still want to introduce the
custom target for convenience so you can trigger moc'ing manually (e.g.
"make moc")...

Michael