[cmake-developers] Automoc in cmake

[Alexander Neundorf]

On Wednesday 08 June 2011, Brad King wrote:
> On 6/8/2011 2:59 PM, Alexander Neundorf wrote:
> > The "two things" are
> > - BSD licensing,  we did that 3 years ago:
> > http://quickgit.kde.org/?p=automoc.git&a=commit&h=78fdba1e2d96bc455125317
> > 48ffb770cb1124798 -and porting to STL+cmsys, we did that now
> 
> Great.  Please push a topic to the stage for review.  Don't
> merge it to 'next' yet though.

It's not that far yet.
You can see current automoc without Qt here:
https://projects.kde.org/projects/kdesupport/automoc/repository/show?rev=no-qt

It is a standalone executable, and to create an executable with automoc you 
have to use one of the macros provided in Automoc4Config.cmake:
https://projects.kde.org/projects/kdesupport/automoc/repository/revisions/no-
qt/entry/Automoc4Config.cmake

i.e. automoc4_add_library() or automoc4_add_executable().

This creates a custom target for the respective target, and writes a file 
which contains the list of course files, include dirs, etc.

When integrating it in cmake, it could simply stay that way, or it could be 
integrated better :-)

At cmake time it needs to know:
-the list of source files
-the target it belongs to

With that, it can generat for buildtime
-the list of source files
-the include directories
-the definitions
-maybe the directory for the target in CMakefiles/ for helper files

This information somehow then at buildtime needs to get into the automoc.
Currently this is a plain text file. If integrated, it might make more sense 
to put that in a cmake script file, so we don't need extra parsing functions.

From the interface for the user, it could be an AUTOMOC argument for 
add_executable/add_library(), or new macros qt[45]_add_executable/library() 
could be created.
This can be done in C++ or cmake script, both should be ok.

At build time, the logic is complex enough and it also has to be really fast 
so that this should IMO be done in the C++.
It could either be a -E automoc <infofile> option, or a -P CMakeAutomoc.cmake 
script, which then calls a new automoc() function.
This then needs to go through the list of source files, and if the file is 
newer than the associated stamp-file or if no stamp-file exists, it needs to 
parse the source file for a #include-moc statement, and if found, execute moc 
to generate this include file.


And we need to make sure it is at least flexible enough for future Qt/moc 
changes.

Alex