Re: [PATCH] diff: Fix rename pretty-print when suffix and prefix overlap

[Philip Oakley <philipoakley@iee.org>]

On 25/02/13 19:50, Antoine Pelisse wrote:
> On Sun, Feb 24, 2013 at 10:15 AM, Junio C Hamano <gitster@pobox.com> wrote:
>> Antoine Pelisse <apelisse@gmail.com> writes:
>>
>>> When considering a rename for two files that have a suffix and a prefix
>>> that can overlap, a confusing line is shown. As an example, renaming
>>> "a/b/b/c" to "a/b/c" shows "a/b/{ => }/b/c".
>>
>> This would be vastly more readable if it had "It should show XXX
>> instead" somewhere in the description, perhaps at the end of this
>> sentence.  It can also be after "thus the { => }" below, but I think
>> giving the expected output earlier would be more appropriate.
>
> Good catch, this would probably be better:
>
>      When considering a rename for two files that have a suffix and a prefix
>      that can overlap, a confusing line is shown. As an example, renaming
>      "a/b/b/c" to "a/b/c" shows "a/b/{ => }/b/c", instead of "a/b/{ => b}/c"
>
>>> Currently, what we do is calculate the common prefix ("a/b/"), and the
>>> common suffix ("/b/c"), but the same "/b/" is actually counted both in
>>> prefix and suffix. Then when calculating the size of the non-common part,
>>> we end-up with a negative value which is reset to 0, thus the "{ => }".
>>
>> In this example, the common prefix would be "a/b/" and the common
>> suffix that does not overlap with the prefix part would be "/c", so
>> I am imagining that "a/b/{ => b}/c" would be the desired output?
>
> Yes, at least that's what I expected.

Surely it would be "a/b/{b => }/c", that is, we have reduced the number 
of b's by one. Or am I misunderstanding something?
(I'm guessing it was an all too obvious typo that was misread)

>
>> This is a really old thinko (dating back to June 2005).  I'll queue
>> the patch on maint-1.7.6 (because 1.7.6.6 is slightly more than one
>> year old while 1.7.5.4 is a lot older) to allow distros that issue
>> incremental fixes on top of ancient versions of Git to pick up the
>> fix if they wanted to.  Perhaps we would want to add a few tests?
>
> I can easily understand why that was missed.
> I will try to resubmit with tests very soon.
Philip