[MERGE] Refactor diffing

[Robert Collins]

On Wed, 2007-11-21 at 15:34 -0500, Aaron Bentley wrote:
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> Robert Collins wrote:
> > I think this is fine as it stands. However I have a proposal about the
> > hooking in of diff that I'd like you to consider.
> > 
> > The use case is to make it possible for external plugins to do things
> > like 'diff gpg keys only'
> > 
> > So I'd like to suggest that you need to classes:
> 
> Took me ages to figure out you meant "two classes".

oops

> > TreeDiffer - a command object 
> >  - show_diff
> >  - from_trees_options
> >  - has a new select_diff(file_id, old_path, new_path, old_label,
> >    new_label) method which returns a Differ instance to use.
> > 
> > Diff(object):
> >     """"Base class for diff operations between files."""
> > 
> >     - has a single public diff method() which returns a result
> >       unchanged/changed/could-not-handle
> 
> It's an interesting goal, but this approach doesn't seem fully-formed to me:
> - - How does select_diff decide which Differ to use?

for differ in self._differs:
    result = differ.diff(file_id, ...)
    if result != CANNOT_DIFF:
        break


> - - What happens if select_diff picks a Differ that returns
>   could-not-handle?  How do we get to the next candidate differ?  It
>   seems simpler to just run call Differ.diff until we find a differ than
>   can handle it.

yah, in actual fact I changed my mind half way through my mail; which
must have added confusion - select_diff was a LBYL which I decided
against in the latter part of the mail.

> - - How would you handle kind changes?

KindChangedDiff coming after BinaryDiff.

-Rob


-- 
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