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RE: Improving the 'diff callbacks'

From: Bert Huijben <bert_at_qqmail.nl>
Date: Tue, 2 Aug 2011 16:23:51 +0200

> -----Original Message-----
> From: Julian Foad [mailto:julian.foad_at_wandisco.com]
> Sent: dinsdag 2 augustus 2011 15:59
> To: Subversion Development
> Subject: RFC: Improving the 'diff callbacks'
> I'm looking at rationalizing the way the client handles diffs, which is
> currently mostly through the "svn_wc_diff_callbacks4_t" interface, with
> some use made of svn_delta_editor_t. I'll loosely abbreviate symbol
> names below, for example "diff_callbacks_t" to refer to the former.
> In libsvn_client, currently:
> Diff what? Producer Interface Consumer
> Normal diff:
> repo-repo svn_ra_do_diff3 + |> diff_callbacks_t |> diff_callbacks
> get_diff_editor | | in diff.c;
> repo-wc svn_ra + svn_wc | | prints diff to
> wc-wc svn_wc_diff6 | | stdout
> Summarizing diff:
> repo-repo svn_ra_do_diff3 |> delta_editor_t |> repos_diff_
> | | summarize.c;
> | | calls sum-cb
> repo-wc not implemented
> wc-wc not implemented
> What's going on here? Why is the summarizing diff output subsystem not
> simply an alternative consumer to the normal diff? If it used the same
> interface, we should be able to plug it straight in.
> First I wondered why the delta_editor_t isn't a suitable interface for
> diffs, and why the WC defines its own 'callback' type for this. One
> reason is because we want a symmetric diff, one that provides the full
> content of both what's added and what's deleted. Although the
> summarizing diff doesn't need to know about file content or property
> deletions, it does want to know about file and directory deletions, so
> that would seem to be a good thing. So why aren't we using the
> diff_callbacks_t here?

Maybe because the diff callbacks transfer the full texts of both before and after a change to provide them to the callback?

The summarize function might have been designed to reduce that overhead?

Received on 2011-08-02 16:24:26 CEST

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