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

[Brad King]

On 01/23/2014 04:08 PM, Alexander Neundorf wrote:
> Any more comments left ?

Moving the discussion from

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/9156/focus=9158

back to the thread where it belongs:

On 01/27/2014 04:58 PM, Stephen Kelly wrote:
> Though I still don't like the behavior in the topic with project() commands
> without a specified VERSION and the
> CMAKE_PROJECT_VERSION_SET_BY_PROJECT_COMMAND variable etc. I don't see why
> all the complexity is needed.
>
> From what I understand, the reason it was added is related to using
> add_subdirectory to add a self-contained/standalone project to host
> buildsystem.

My main concern that the VERSION complexity solves is for changing
behavior of existing projects that are *not* modified at all.  We've
established that a project() without VERSION needs to unset the
PROJECT_VERSION variables because otherwise they would not correspond
to the current PROJECT_NAME.  However, an existing project could do

 # CMakeLists.txt
 project(Top)
 set(PROJECT_VERSION 1.0.0)
 add_subdirectory(Sub)

 # Sub/CMakeLists.txt
 project(Sub)
 message(STATUS "Top version = ${PROJECT_VERSION}")

Since previous versions of CMake documented no special behavior
for the PROJECT_VERSION variable this code is completely fine
now, but would suddenly change in behavior if project() started
to unset PROJECT_VERSION.

So our options are

(1) Design new behavior in a way that requires a change to the
    project to activate.

(2) Add a policy.  The policy should only trigger when the
    project() command is about to unset a PROJECT_VERSION
    variable that was set by user code and not by a previous
    project() command.

-Brad