Allow for multiple projects to have the same versions

[Cinc-th]

This is a follow up ticket to #12031 which dealt with multiple milestones per project.

For allowing multiple projects for a version multiple changes to the version creation process in version.py are necessary. It may be a good idea to start from scratch using version.py​ from ExtendedVersionPlugin (which is very similar).

While adding this feature a proper SMPVersion model similar to Trac Version should be created. This may make the filtering code for the roadmap (see #10087) a little bit more obvious. Same goes for a proper SMPMilestone model.

[anonymous]

Multiple projects can share the same version, but this has to be defined at the time the version is created.

Scenario: Project A is at v2.0 Project B is at v2.0 A ticket is created for next Project A version (v2.0.1) and a new project is defined and associated with the project Some time after, it is decided that there will be additional work done on Project B. When you attempt to create a v2.0.1 and assign to Project B, you get a version already exists error.

Workaround: Delete the v2.0.1 Create a new v2.0.1 and associate with Project A and Project B

The workaround is a big bummer because it would be easy for the user to make an error.

If the "Edit Version" page could be modified to showed the project list with checkboxes, then this would allow you to just go to v2.0.1 and add Project B to the list.

I don't believe that this would require any changes to the DB structures..

[Cinc-th]

The version admin page already allows to add one or more projects to any version.

You may force single projects for each version with the following configuration option in trac.ini:

[simple-multi-project]
single_project_versions = True

Surprisingly the version pages you access from the roadmap don't offer this feature for some reason. Since these pages will be removed for now because of #13849 expect no changes there.