bug#54034: 29.0.50; Diff prettify broken for empty files

[Basil L. Contovounesios]

Matthias Meulien [2022-04-07 14:15 +0200] wrote:

> From: Matthias Meulien <orontee@gmail.com>
> Date: Thu, 7 Apr 2022 00:11:55 +0200
> Subject: [PATCH] Display file mode information when diff font lock prettify
>  enabled
>
> * lisp/vc/diff-mode.el (diff--font-lock-prettify): Make regexp capture
> file mode information.

I think this gave rise to the following regression in the header when
diff-font-lock-prettify is enabled:

0. emacs -Q
1. M-x diff-buffers RET RET RET
   [ Header now comprises 'diff -u ...'. ]
2. (setq diff-font-lock-prettify t) C-x C-e
3. C-x o g
   [ Header is now 'Deleted file'. ]

It's not particularly jarring to see a header like that when diffing
non-file-visiting buffers, but more importantly the same header appears
when diffing any regular files via M-x diff.

Thanks,

-- 
Basil