About IBranchingVC...

[Matthew Woehlke]

Matt Rogers wrote:
> On Thursday 17 May 2007 14:24, Matthew Woehlke wrote:
>> How exactly is branch() supposed to work? In perforce, a "tag" (label)
>> requires the source files to be checked out, while a branch() requires
>> the destination to be in the view (branch() == copy() except somewhat
>> more sophisticated). Also there is a "branch" object that would
>> (should?) be created in this case. Also labels in perforce need a name
>> (no surprise here).
>>
>> In svn AFAIK both branch() and tag() are synonyms for copy(). I don't
>> know how things work in CVS.
>>
>> Options:
>> - move branch() to IRepositoryVC and drop tag()
> 
> nope, people need to tag and branch things for certain VCSs but not all of 
> them require branching or tagging. Branching and tagging need their own 
> interface.

Clarification: tag() would move to IFooVC, e.g. ISubversionVC, ICvsVC, 
etc. The generic interfaces are for things that can be shared between 
two or more VCS's.

>> - perforce doesn't implement IBranchingVC
> 
> nope, because it obviously does some sort of branching

Yes, but the semantics are different from how branching is done in other 
VCS's. Also see above.

>> - clarify what branch() and tag() do in a way that is favorable to a
>> perforce implementation
> 
> hmm, also no. why should our interfaces favor perforce or any other version 
> control system, subversion and cvs included?

They have to, if they are going to be generic interfaces. :-) (Well, 
really they have to be defined in a way that lets as many VCS's as 
possible implement them.)

>> - drop IBranchingVC altogether; plugins will expose the VCS's native flavor
> 
> nope. We can have an interface for branching, it's a universal task.

If it's a "universal task" then IBranchingVC has no business existing 
and branch() belongs in IBasicVC. IIRC IBasicVC is the only non-optional 
interface. So... your preference? ;-)

>> In any case, "branches" can still be done using copy() from IBasicVC for
>> the generic case, otherwise plugins are expected to expose the VCS's
>> native flavor of this.
> 
> branching is a term that is universally understood. It has an equivalent for 
> nearly all version control systems. (the exceptions being the distributed 
> ones like git or darcs, which probably wouldn't implement the IBranchingVC 
> interface anyways). If needed, the VCS plugin should take the steps needed to 
> make a branch or a tag, even if we use a temporary directory for it.

The problem is for perforce to implement a "generic" branch, it has to 
invent a temporary client, which I consider to be 'an ugly hack' (keep 
in mind that once you do this, the name of said client lives forever). 
When I brought this up previously, Andreas agreed that we would rather 
not do this sort of thing. Given what must/should be done to create a 
branch in perforce, I feel that the best place for the perforce plugin 
to implement branch() is in IPerforceVersionControl.

Or we could make branch() look like:

branch( <what to branch>, <where to put it>,
         QString nameOfBranch,
         QString nameOfTemporaryClient );

...where VCS's may ignore the last two arguments. I would probably do 
something similar with tag() in that case, take a source, destination, 
and name, where one of the latter two is ignored.

-- 
Matthew
/bin/sh -- still Bourne on Solaris (and still not POSIX compliant)