On Tue, Apr 02, 2013 at 02:15:17PM -0700, Junio C Hamano wrote:
> John Keeping <j...@keeping.me.uk> writes:
> > When the source file is empty, the calculation of the merge score
> > results in a division by zero. Since the merge score is initialized to
> > zero, it makes sense to just leave it as it is if the source size is
> > zero. This means that we still use the extent of damage metric to
> > decide whether to break the filepair.
> Well spotted. An empty blob to another blob that is larger than 400
> bytes will trigger div0, and it makes sense to leave merge-score to
> 0 (i.e. do not show as whole-delete-then-whole-add after rename
> detection is done and the broken filepair is merged back).
> Actually, if src->size is 0, we probably shouldn't break the filepair
> in the first place. That is, if your preimage and postimage looked
> like these:
> == preimage == == postimage ==
> F (empty file) F (a large file)
> E (a new empty file)
> do we want to see F renamed to E and then a new file created as F
> while running "git diff -B -M"? I doubt it.
> So in that sense, this might be a better solution. I dunno.
I considered this, but didn't quite understand the code well enough to
be sure that was the right thing to do. Does it make sense to bail out
early if dst->size is zero as well?
The message for commit 6dd4b66 (Fix diffcore-break total breakage)
indicates that "don't bother to break small files" is wrong in some
cases, but it I wonder if "don't bother to break empty files" is okay.
> diffcore-break.c | 2 ++
> 1 file changed, 2 insertions(+)
> diff --git a/diffcore-break.c b/diffcore-break.c
> index 44f8678..eabafd5 100644
> --- a/diffcore-break.c
> +++ b/diffcore-break.c
> @@ -67,6 +67,8 @@ static int should_break(struct diff_filespec *src,
> max_size = ((src->size > dst->size) ? src->size : dst->size);
> if (max_size < MINIMUM_BREAK_SIZE)
> return 0; /* we do not break too small filepair */
> + if (src->size == 0)
> + return 0; /* we do not let empty files get renamed */
> if (diffcore_count_changes(src, dst,
> &src->cnt_data, &dst->cnt_data,
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