bug#59962: 29.0.60; vc commands fail in diff-mode

[Sven Joachim <svenjoac@gmx.de>]

On 2022-12-11 17:46 +0100, Daniel Martín wrote:

> Sven Joachim <svenjoac@gmx.de> writes:
>
>> As a distribution maintainer, I find myself working with
>> version-controlled patches which Emacs visits in diff-mode.
>> Unfortunately, there is a bad interaction between diff-mode and vc,
>> which makes all vc commands fail.  This is what I got on C-x v l:
>>
>> ,----
>> | Debugger entered--Lisp error: (wrong-type-argument arrayp nil)
>> |   file-truename(nil)
>> |   find-buffer-visiting(nil)
>> |   vc-buffer-sync-fileset((Git (nil nil nil nil) nil nil patch) t)
>> |   vc-diff(nil t)
>> |   funcall-interactively(vc-diff nil t)
>> |   call-interactively(vc-diff nil nil)
>> |   command-execute(vc-diff)
>> `----
>>
>
> Could you detail the steps to reproduce this issue (preferably from
> emacs -Q)?  I've tried C-x v l on a few Git-version-controlled .patch
> files (in Diff mode) but I couldn't reproduce the error.  Thanks.

$ git clone https://salsa.debian.org/xorg-team/app/xterm.git

Then visit any of the xterm/debian/patches/*.diff files and type
C-x v l.

Cheers,
       Sven