[CMake] Re: Re-running automoc all the time after #13494

[Jan Kundrát]

Hi, is there a solution for automoc being re-run every time when the binary 
directory is in the include path (see below)?

Cheers,
Jan

On Wednesday, 31 July 2013 11:43:48 CEST, Jan Kundrát wrote:
> Hi folks,
> I am using out-of-tree builds with Trojita [1], a Qt 
> application. My cmake version is 2.8.10.2 on Gentoo Linux using 
> the default Makefile generator and GNU make.
>
> Some of my .cpp files #include "ui_something.h", which are 
> generated by moc. Other files are imported from 3rd party 
> projects and directly include moc_*.cpp. In order to make this 
> work, my code calls:
>
>   include_directories(${CMAKE_CURRENT_BINARY_DIR})
>   set(CMAKE_AUTOMOC True)
>
> However, it looks that due to a fix for #13494 [2], moc gets 
> re-run whenever I run `make`. The build system is apparently 
> smart enough to not re-link everything, but it nonetheless takes 
> at least 3.5 seconds of real time when using non-parallel builds 
> (and 1.7 seconds when building with -j6, which I sometimes 
> cannot use because I have "only" 4GB of RAM on this machine, 
> Thinkpad T420s with i5-2520M and an Intel SSD).
>
> I guess what I'm looking for is a way of telling cmake to add 
> -I${CMAKE_CURRENT_BINARY_DIR} only when calling the actual 
> compiler, not moc. Is that possible? Or shall I do it some other 
> way?
>
> I guess that I could probably split the static library I'm 
> building into two units, one for the generated files and the 
> other for actual sources, and set the include directory only 
> when building the second library (via target-specific 
> properties). I'm not sure how easy it is to persuade automoc to 
> work in such a setup, though.
>
> Another annoyance is that I want to support cmake 2.8.7 as well 
> (that's what gets shipped with Ubuntu 12.04 LTS) which does not 
> support target-specific includes. My cmake setup is annoyingly 
> complicated due to this requirement already, and I'd like to 
> keep it in a maintaineable state :). General comments on the 
> readability of the existing cmake setup are much appreciated as 
> well -- perhaps I'm doing something in a completely wrong way, 
> after all.
>
> With kind regards,
> Jan
>
> [1] 
> http://quickgit.kde.org/?p=trojita.git&a=blob&h=4ac8397d028bec11e636affc72c2c014e8b8e756&hb=b870be05017674781bc52c48934c9800a6329493&f=CMakeLists.txt
> [2] http://public.kitware.com/Bug/view.php?id=13494
>

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