config.h.cmake issue ?

[David Faure]

On Wednesday 03 May 2006 15:32, Ralf Habacker wrote:
> 	#cmakedefine HAVE_PCREPOSIX 1
> 
> The problem is that if someone forgets to add this constants the resulting errors are hards to detect. 

We could fix this by using #if HAVE_FOO and #if !HAVE_FOO instead of ifdef,
then we would have compiler warnings when HAVE_FOO isn't defined (due to forgetting
to add it to config-foo.h, or due to forgetting to include config-foo.h in the cpp file).

But for this we need a #cmakedefine equivalent that sets 0 or 1, instead of "undef or 1".
Could this be done?

> Another example I encountered was the preparation of the CMakeLists.txt for a dbus test build.
> I took the config.h.cmake from kdecore and added it to the dbus sources. 
> Now I had to disable all not required #cmakedefine by hand, which wasn't very easy to detect. 
> And if I had forgotten one, this was only detected by an compiler error, so this ends up in an iterative process until i had fixed this area.    

I can't see why you started from the huge, monolithic, unsplit, config.h.cmake from kdecore...
I would have collected the HAVE_ needed by the code, and put those into config.h.cmake.

> Now imagine there is an developer, who adds stuff to a package which uses cmake and it new to cmake.
> He adds and Find....cmake from another package and is thinking, thats all, but unfortunally he had to add
> the #cmakedefine by hand, which will be probably forgotten after a time not working with the build system.   
I don't really agree, since this is also how it worked with autoconf, you had to add something to config.h.in.

> macro_optional_find_package(PCRE,HAVE_PCREPOSIX)
That's really too simplified, there could be multiple defines to make, and it doesn't say where the output should go....
I think what you want is more like 

  macro_optional_find_package(PCRE)
  add_define( ${CMAKE_CURRENT_BINARY_DIR}/global.h PCRE_FOUND HAVE_PCREPOSIX )

which would add #define HAVE_PCREPOSIX 1 in global.h (and create that file if necessary)
if PCRE_FOUND is true  [and 0 otherwise, if we agree about switching to #if - but this should
probably be an option to add_define]. 
It would also have to check if global.h already defines it to the right value, to avoid 
making unnecessary changes to the global.h file.

-- 
David Faure, faure at kde.org, sponsored by Trolltech to work on KDE,
Konqueror (http://www.konqueror.org), and KOffice (http://www.koffice.org).