How to open branch object equivalent of -r ancestor::parent

[Alexander Belchenko]

Aaron Bentley пишет:
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> On 12-03-16 11:41 AM, Alexander Belchenko wrote:
>> To fix the bug https://bugs.launchpad.net/bzr-explorer/+bug/956268 
>> I need to open ancestor related to parent branch instead of tip of 
>> parent branch itself.
>>
>> Current code does today:
>>
>> old_branch =
>> mod_branch.Branch.open_containing(branch.get_parent())[0]
>>
>> Which is equivalent of -r branch::parent
>>
>> I need this to be changed to be equivalent -r ancestor::parent
>>
>> Any suggestions or code snippets will help.
> 
> What you ask is technically possible, but the difference between -r
> branch::parent and -r ancestor::parent is the *revision* they select,
> not the branch they open.

Yes, you're right. I don't need a branch object actually, for 
obtaining delta between 2 tree states I need tree object corresponding 
to that revision. Thank you for your example! Having revision id I 
should be able to obtain revision tree to compare with.

> 
> We'll need the revision anyhow, so let's start there.  To get the
> revision used by ancestor::parent, you'll need to
> 
> # Ensure you have both branches open
> old_branch = mod_branch.Branch.open(branch.get_parent())
> # Get a graph, so you can find the common ancestor (LCA)
> graph = old_branch.repository.get_graph(branch.repository)
> # Find the LCA of the revisions
> lca = graph.find_unique_lca(branch.last_revision(),
>                             old_branch.last_revision())
> 
> That should give you the revision you need to diff against.
> 
> If you really need to specify a branch, not a revision, then I guess
> you can make a memory branch, stacked on either of the other branches,
> and call Branch.set_last_revision_info(1, lca) on it.  But I recommend
> avoiding this if at all possible.
> 
> Aaron
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