[MERGE] trees - add get_parent_ids

[Robert Collins]

On Fri, 2006-06-16 at 10:01 -0400, Aaron Bentley wrote:
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> Robert Collins wrote:
> > This patch adds a get_parent_ids() call to all our tree objects (at
> > least, I think to all of them ;)).
> > 
> > This call returns:
> > [] for a tree with unknown parents
> 
> I think this should be something other than the empty list.  Possibly an
> exception.
> 
> > ['null:'] for a tree descending from null:
> 
> e.g. revno 1, right?

revno 1 yes.

> > [revid, ...] in general.
> > 
> > EmptyTree descends from ['null:'].
> 
> EINFINITELOOP.  EmptyTree doesn't descend from 'null:', it *is* 'null:'.
>  EmptyTree should return [], because 'null:' does not descend from 'null:'.

Ah, ok.

> > RevisionTree mirrors the revision graph.
> > WorkingTree provides the union of last_revision and pending merges.

How about I change the api to be:
[] for a tree known to have no parents including EmptyTree.
[revid, ...] for trees descending from non-null parents.
raises BzrError *for now* if we do not know the parents. (When we have a
use for it, we can and should create a specific exception. I'm just not
sure what it should be called, and as we have no code that can generate
this situation I'm hesitant about putting in an exception that may never
ever be used/possible to use.

Rob

-- 
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