[MERGE/RFC] Use Branch.pull() to update master branch.

[John Arbash Meinel]

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Jelmer Vernooij wrote:
> The attached patch makes the commit code use Branch.pull() to update the
> master branch when committing to a bound branch. 
> 
> This is required for bzr-svn as it can't update just the repository, it
> has to update the branch as well. Previously it had some magic in the
> Repository.fetch() code to handle this, but that is vulnerable to race
> conditions. (#248289)
> 
> Is Branch.pull() the right call here, or should I be adding something
> custom?
> 
> Cheers,
> 
> Jelmer
> 

This might be ok. I think the main problem is that we can't update
self.last_revision until after the data has been fetched to the master.
So 'new_rev_id' doesn't *exist* in the source branch. So the code
as-written means that branches must support pull() with a revision that
is not in their ancestry.

BB:comment

John
=:->

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