Re: "git diff --ignore-space-change --stat" lists files with only whitespace differences as "changed"

[Jeff King <peff@peff.net>]

On Wed, Jan 18, 2017 at 12:57:12PM -0800, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > So I dunno. A sensible rule to me is "iff -p would show a diff header,
> > then --stat should mention it".
> 
> True but tricky (you need a better definition of "a diff header").
> 
> In addition to a new and deleted file, does a file whose executable
> bit was flipped need mention?  If so, then "diff --git" is the diff
> header in the above.  Otherwise "@@ ... @@", iow, "iff -p would show
> any hunk".
> 
> I think the patch implements the latter, which I think is sensible.

I would think the former is more sensible (and is what my patch is
working towards). Doing:

  >empty
  git add empty
  git diff --cached

shows a "diff --git" header, but no hunk. I think it should show a
diffstat (and does with my patch).

I was thinking the rule should be something like:

  if (p->status == DIFF_STATUS_MODIFIED &&
      !file->added && !file->deleted))

and otherwise include the entry, since it would be an add, delete,
rename, etc, which carries useful information.

Though a pure rename would not hit this code path at all, I would think
(it would not trigger "!same_contents"). And a rename where there was a
whitespace only change probably _should_ be omitted from "-b".

Ditto for a pure mode change, I think. We do not run the contents
through diff at all, so it does not hit this code path.

-Peff