[CMake] General modernization facility

[James Bigler]

Brandon Van Every wrote:
> On Dec 18, 2007 9:36 AM, James Bigler <bigler at cs.utah.edu> wrote:
>> I also agree that trying to maintain backwards compatibility to the
>> detriment of the future can become a hinderance.  I just had a
>> collegue who was extreemly frustrated for several hours with why his
>> build didn't work, only to discover that he should have been using
>> ADD_SUBDIRECTORIES instead of SUBDIRS.  There was no warning from
>> CMake stating that he shouldn't be using it (I would argue that CMake
>> should warn about the use of SUBDIRS).
> 
> General warning facilities, and a standard way of turning on future
> looking options, so that people do not have to be stuck in the past if
> they don't want to be, would be good.   CMake CVS has the
> set_properties(GLOBAL PROPERTIES var1 value1 var2 value2 ...)
> mechanism.  So if we didn't bother with the bool(var [value])
> interface I proposed, we could selectively apply Alex's patch using
> set_properties(GLOBAL PROPERTIES ORDINARY_Y_N_STRINGS TRUE).  Or maybe
> someone can think of a better name for it.
> 
> Collections of options such as this could be put in a standard module
> called "Modern."  include(Modern) would turn on improvements that are
> clearly desirable but break backwards compatibility.  Flagging SUBDIRS
> as an error would be the kind of thing you'd stick into Modern.  If a
> user does include(Modern), they're saying they want whatever is
> currently considered the best practice, even if that breaks something.
>  It should be clearly documented as having that purpose.
> 
> Heh, I wonder if in some instances the opposite would be needed,
> include(Ancient) !  :-)  Something that either suppresses appeals to
> modernity, or warns vehemently against them.

Perhaps this could be enforced by CMAKE_BACKWARDS_COMPATIBILITY variable.  If you supply a sufficiently modern version of cmake, then deprecated things will turn on 
warnings/errors.  If you set the version lower, then features that were not deprecated at that version wouldn't issue warnings.

James