[CMake] How to properly handle build version number in CMake script for project

[Robert Dailey]

OK weirdly, tested again, this also works and is a little more
simplified (although more confusing, since now we're intermixing
non-cache and cache variables with the same name; behavior is not
exactly clear, or well-defined.

if( BUILD_VERSION )
    set( BUILD_VERSION ${BUILD_VERSION} )
    unset( BUILD_VERSION CACHE )
else()
    set( BUILD_VERSION 7.1.1.2 )
endif()

On Mon, Apr 10, 2017 at 1:32 PM, Robert Dailey <rcdailey.lists at gmail.com> wrote:
> Actually this seems to work:
>
> if( BUILD_VERSION )
>
>     set( version_override ${BUILD_VERSION} )
>     unset( BUILD_VERSION CACHE )
>     set( BUILD_VERSION ${version_override} )
>     unset( version_override )
>
> else()
>
>     set( BUILD_VERSION 7.1.1.2 )
>
> endif()
>
> It's a bit messy but gets the job done, and doesn't require
> configure_file(). Maybe there is a way to clean this up even more?
>
> I noticed that unset( BUILD_VERSION CACHE ) actually unsets non-cache
> versions of a variable too, so I had to use the temporary variable to
> transfer the value.
>
> On Mon, Apr 10, 2017 at 1:15 PM, Robert Dailey <rcdailey.lists at gmail.com> wrote:
>> Sorry you're right, this isn't working because -D creates a cache
>> entry for the variable, which breaks it.
>>
>> So maybe more ideas on the configure_file() solution would be ideal...
>> unsetting the cache variable might work as well, I have to toy around
>> with this.
>>
>> On Mon, Apr 10, 2017 at 12:48 PM, Bruce Stephens
>> <bruce.r.stephens at gmail.com> wrote:
>>> On Mon, Apr 10, 2017 at 5:04 PM, Robert Dailey <rcdailey.lists at gmail.com> wrote:
>>>> Actually I think your idea does work. Why do you think it won't? I'm
>>>> using it right now and so far it seems OK.
>>>
>>> I assumed (without testing, admittedly) is that it would fail if
>>> someone used -D to set the value,
>>> then changed some CMakeLists.txt file, then executed the build command
>>> again. I'd expect that
>>> to rerun cmake to update the build files and I'd fear that you'd then
>>> get BUILD_VERSION from
>>> the CMakeLists.txt file rather than the value explicitly set.
>>>
>>> However, I haven't tried it, and maybe it works fine (with the
>>> generators you care about) even without
>>> caching?