[CMake] PKGCONFIG backward compatibility on CVS trunk.

[Michel Hermier]

Alan W. Irwin wrote:
>
> It appears the 2.4.5 version of UsePkgConfig.cmake is what you need. I
> therefore believe the current approach in cvs (although it works
> consistently for PLplot for 2.4.5 and cvs version) is attempting the
> impossible; emulate the old behaviour by using the modern macros with
> post-processing to attempt to make the result _exactly_ compatible.
>
> Therefore, I suggest the following improved proposal to take care of 
> these
> compatibility issues exactly.
>
> 1) Copy the 2.4.5 UsePkgConfig.cmake which defines the PKGCONFIG macro to
> CVS with the only change being to add a message that it is an obsolete
> macro.  Then you _know_ that if the user uses UsePkgConfig.cmake they 
> will
> automatically be compatible with what was done before.
>
> 2) Get rid of the emulated definition of the PKGCONFIG macro that is
> currently in FindPkgConfig.cmake.  In other words, FindPkgConfig.cmake is
> completely reserved for the new pkg-config stuff and does not try to 
> emulate
> the old PKGCONFIG macro.
>
> I attach a patch to current CVS that implements this proposal.  It works
> for PLplot.
>
> Michel, does this patch work for you?
The patch did the trick (as expected) thought it doesn't apply cleanly 
for me due to whitespace.

Anyway maybe the inclusion of the file should also be restricted by some 
version compatibility checking ?
So that a project say by macro that it requires a 2.4.5 compatibility 
and only warn about the deprecated helper file and/or macro, while a 
macro not saying it will output a error message on deprecated file 
usage, and skip the content definition ? So that it helps version 
migration ?

Cheers,
    Michel