Re: diff-index --cc no longer permitted, gitk is now broken (slightly)

[Jeff King <peff@peff.net>]

On Mon, Aug 30, 2021 at 04:05:50PM +0300, Sergey Organov wrote:

> > Is gitk wrong to add --cc unconditionally? Should it do so only when
> > there are conflicts? Or not at all?
> 
> As far as I can tell, --cc had no effect on diff-index, it was just
> silently consumed. If I'm right, this line in gitk never needed --cc.
> Then either gitk is to be fixed, or we can "fix" diff-index to silently
> consume --cc/-c again, for backward compatibility.

I think it does have an effect. Try this to generate a simple merge
conflict:

  git init repo
  cd repo

  echo base >file
  git add file
  git commit -m base

  echo main >file
  git commit -am main

  git checkout -b side HEAD^
  echo side >file
  git commit -am side

  git merge main ;# maybe master here depending on your config

And then with pre-v2.33 Git, --cc does a combined diff:

  $ git.v2.32.0 diff-index -p  HEAD
  diff --git a/file b/file
  index 2299c37..81768df 100644
  --- a/file
  +++ b/file
  @@ -1 +1,5 @@
  +<<<<<<< HEAD
   side
  +=======
  +main
  +>>>>>>> main

  $ git.v2.32.0 diff-index --cc HEAD
  diff --cc file
  index df967b9,2299c37..0000000
  --- a/file
  +++ b/file
  @@@ -1,1 -1,1 +1,5 @@@
  - base
  ++<<<<<<< HEAD
  + side
  ++=======
  ++main
  ++>>>>>>> main

Likewise, --raw will show a combined diff, though it's a bit less useful
because the unmerged entry has a null sha1:

  $ git.v2.32.0 diff-index HEAD
  :100644 100644 2299c37978265a95cbe835a4b0f0bbf15aad5549 0000000000000000000000000000000000000000 M	file

  $ git.v2.32.0 diff-index --cc --raw HEAD
  ::100644 100644 100644 df967b96a579e45a18b8251732d16804b2e56a55 2299c37978265a95cbe835a4b0f0bbf15aad5549 0000000000000000000000000000000000000000 MM	file

-Peff