[cmake-developers] RFC: add version to project() call

[Alexander Neundorf]

On Sunday 19 January 2014, Alexander Neundorf wrote:
> On Wednesday 15 January 2014, Matthew Woehlke wrote:
> > On 2014-01-15 16:25, Alexander Neundorf wrote:
> > > On Wednesday 15 January 2014, Alexander Neundorf wrote:
> > >> And, to actually produce the breakage, at some place the VERSION
> > >> argument must have been added.
> > >> With the current state of my branch, this could be worked around by
> > >> unsetting the guard variable:
> > >> 
> > >> 
> > >> project(Foo VERSION 1.2.3)
> > >> ....
> > >> 
> > >> unset(CMAKE_PROJECT_VERSION_SET_BY_PROJECT_COMMAND)
> > >> add_subdir(B)
> > >> 
> > >> This way B would be protected from that change in behaviour.
> > > 
> > > I could also add more logic, to try to detect if PROJECT_VERSION has
> > > been set manually, e.g. project() could reset PROJECT_VERSION only if
> > > it has the same value as ${${ParentProjectName}_VERSION}. Then it
> > > would only break if there was a manual set(PROJECT_VERSION ...) before
> > > a project() call without VERSION, and if that manually set version was
> > > the same as the version in the "parent project".
> > 
> > IMHO your last suggestion (very good idea, btw!) is more than adequate,
> > especially given the original weakness of my "objection" (which was
> > always more along the lines of "did you consider this case, and should
> > we worry about it?").
> 
> This is now in the AddVersionToProjectCommand branch on git stage.
> 
> Please have a close look at it.
> 
> I'm not sure I like that somewhat magic behaviour how it decides whether to
> unset() the variables or not.
> There will be problems with this very rarely, but when the circumstances
> occur, it may be quite hard to figure out.
> I.e. it could happen when the version number of a sub-project changes, then
> suddenly PROJECT_VERSION could be empty afterwards:
> 
> CMakeLists.txt:
> 
> project(Parent VERSION 1.0.0)
> 
> add_subdirector(sub)
> 
> sub/CMakeLists.txt:
> - set(PROJECT_VERSION 0.0.1)
> + set(PROJECT_VERSION 1.0.0)
>   project(Foo)
>   message(STATUS "Version: ${PROJECT_VERSION})
> 
> Such a patch would have the effect that PROJECT_VERSION in suddenly empty
> in the message() call.
> 
> I would probably prefer to not touch the PROJECT_VERSION variables at all
> if VERSION is not used, then there are at least no (very rare) surprises
> or sudden breakages.
> 
> Alex

I could maybe also do something with variable_watch(), but I haven't used this 
yet at all. It probably would have somne performance impact I guess.

Alex