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Re: svn_diff.h truncated

From: Stefan Sperling <stsp_at_elego.de>
Date: Tue, 8 Feb 2011 22:50:29 +0100

On Tue, Feb 08, 2011 at 10:45:03PM +0100, Johan Corveleyn wrote:
> On Tue, Feb 8, 2011 at 9:01 PM, Johan Corveleyn <jcorvel_at_gmail.com> wrote:
> > On Tue, Feb 8, 2011 at 1:28 PM, Daniel Shahaf <d.s_at_daniel.shahaf.name> wrote:
> >> I ran into this while trying to 'svn up' today, and managed to reproduce
> >> it in another working copy:
> >>
> >> % svn revert -R .
> >> % cat ./before
> >> Index: subversion/include/svn_diff.h
> >> ===================================================================
> >> --- subversion/include/svn_diff.h       (revision 1067829)
> >> +++ subversion/include/svn_diff.h       (working copy)
> >> @@ -198,7 +198,7 @@
> >>  svn_error_t *
> >>  svn_diff_diff_2(svn_diff_t **diff,
> >>                 void *diff_baton,
> >> -                const svn_diff_fns2_t *diff_fns,
> >> +                const svn_diff_fns2_t *diff_fns2,
> >>                 apr_pool_t *pool);
> >>
> >>  /** Given a vtable of @a diff_fns/@a diff_baton for reading datasources,
> >> @@ -224,7 +224,7 @@
> >>  svn_error_t *
> >>  svn_diff_diff3_2(svn_diff_t **diff,
> >>                  void *diff_baton,
> >> -                 const svn_diff_fns2_t *diff_fns,
> >> +                 const svn_diff_fns2_t *diff_fns2,
> >>                  apr_pool_t *pool);
> >>
> >>  /** Given a vtable of @a diff_fns/@a diff_baton for reading datasources,
> >> @@ -252,7 +252,7 @@
> >>  svn_error_t *
> >>  svn_diff_diff4_2(svn_diff_t **diff,
> >>                  void *diff_baton,
> >> -                 const svn_diff_fns2_t *diff_fns,
> >> +                 const svn_diff_fns2_t *diff_fns2,
> >>                  apr_pool_t *pool);
> >>
> >>  /** Given a vtable of @a diff_fns/@a diff_baton for reading datasources,
> >> % patch -p0 < ./before
> >> % svn up -q subversion/include/
> >> % cat -n subversion/include/svn_diff.h | tail
> >>   296   * Differences, similarities, and conflicts are described by lining up
> >>   297   * "ranges" of data.
> >>   298   *
> >>   299   * @note These callbacks describe data ranges in units of "tokens".
> >>   300   * A "token" is whatever you've defined it to be in your datasource
> >>   301   * @c svn_diff_fns_t vtable.
> >>   302   */
> >>   303  typedef struct svn_diff_output_fns_t
> >>   304  {
> >>   305    /* Two-way and three-way diffs both call the first two output functions: */
> >> %
> >
> > Wow, weird. I can reproduce it too. I'm looking into it.
>
> I'm continuing to try and fix this. For now, some thoughts I typed on IRC:
>
> [22:29] <@jcorvel> ok, I'm starting to understand the truncating business
> [22:30] <@jcorvel> diff is not affected, because it only outputs the
> modified stuff from the diff chain
> [22:30] <@jcorvel> (with their context)
> [22:30] <@jcorvel> but diff3 outputs the entire chain ...
> [22:31] <@ehu> which is missing its last record?
> [22:31] <@jcorvel> yes
> [22:31] <@ehu> evil
> [22:32] <@jcorvel> I don't add the suffix to that diff chain (except
> the first 50 lines, because I don't consider them part of the
> identical suffix, to help diff/blame find a good way to output it)
> [22:33] <@jcorvel> that was really an early optimization (when I was
> only focusing on diff2): I saw that it didn't need the identical
> suffix to do its work correctly
> [22:33] <@jcorvel> that way, I could avoid counting lines while
> scanning the identical suffix (which I do need to do for prefix
> scanning, but I thought I could get away with it for the suffix)
> [22:34] <@jcorvel> only later I included diff3 and diff4, and
> considered everything ok when the test-suite passed
> [22:34] <@jcorvel> if there would have been a merge test with more
> than 50 common lines at the end, that test would have failed ...
> [22:36] <@jcorvel> so, there are a couple of ways to fix this:
> [22:36] <@jcorvel> 0. remove suffix scanning
> [22:36] <@jcorvel> 1. make suffix scanning count lines, so it can
> include a "common" diff chunk at the end of the chain, with the
> correct nr of lines
> [22:37] <@jcorvel> 2. have some way for a diff chunk in that chain to
> indicate "until the end", and make svn_diff_file_output_merge2 cope
> with that
> [22:37] <@jcorvel> that's all I can think of right now
>
> Any opinions on which solution I should pursue? For now, I'm looking
> at how difficult 2. would be. But if it takes too long, maybe I should
> simple do 0. to eliminate potential wc corruption for people working
> with trunk svn ...

I'd suggest commit something for approach 0 now (but don't remove lots
of code, a simple #ifdef or some other way of avoiding to call the code
is fine). And then look into 1 or 2 :)
Received on 2011-02-08 22:51:13 CET

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