[svn.haxx.se] · SVN Dev · SVN Users · SVN Org · TSVN Dev · TSVN Users · Subclipse Dev · Subclipse Users · this month's index

Re: svn_diff.h truncated

From: Johan Corveleyn <jcorvel_at_gmail.com>
Date: Wed, 9 Feb 2011 00:29:45 +0100

On Tue, Feb 8, 2011 at 11:19 PM, Johan Corveleyn <jcorvel_at_gmail.com> wrote:
> On Tue, Feb 8, 2011 at 10:50 PM, Stefan Sperling <stsp_at_elego.de> wrote:
>> 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 :)
>
> Ok, done: r1068613
>
> That takes the pressure off a bit. Though I really wouldn't want to
> lose that half of the optimization :-(, so I'll continue working on a
> better fix ...

I think I'd better go for option 1: counting lines while
suffix-scanning, so the entire diff chain is correct. Seems like the
safe thing to do. Special casing while outputting the diff/merge seems
like a bad idea.

Pfff, instantly getting tired. I feel a lot of work coming up (the
suffix scanning was already a lot more complex than the prefix
scanning). Oh well, what else is new...

-- 
Johan
Received on 2011-02-09 00:30:44 CET

This is an archived mail posted to the Subversion Dev mailing list.