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

On Sun, Feb 24, 2013 at 10:15 AM, Junio C Hamano [off-list ref] wrote:

Antoine Pelisse [off-list ref] writes:

quoted

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"

quoted

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.

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.