bug#65049: Minor update to the repro steps

[Dmitry Gutov]

On 28/08/2023 19:12, Eli Zaretskii wrote:
> > Date: Mon, 28 Aug 2023 16:45:23 +0300
> > Cc:juri@linkov.net,habamax@gmail.com,65049@debbugs.gnu.org
> > From: Dmitry Gutov<dmitry@gutov.dev>
> >
> > On 28/08/2023 15:12, Eli Zaretskii wrote:
> > > > Try edebug-instrumenting vc-diff-internal and then calling vc-root-diff
> > > > anywhere (C-x v D). When the execution reaches the line that we have
> > > > been discussing, you'll see that (vc-coding-system-for-diff (car files))
> > > > evaluates to 'undecided because (car files) is a directory.
> > > >
> > > > So this mechanism is always unused in vc-root-diff.
> > > OK, but in that case 'undecided' is the best guess we can come up
> > > with.  It basically lets Emacs guess when it actually sees the stuff
> > > in the diffs, while reading it into a buffer.
> > Yes, and if it's good enough for the (possibly?) most-frequently used
> > out of the vc-*-diff commands, then perhaps we don't need the additional
> > detection logic?
> >
> > Since its introduction 30 years ago indeed the situation has changed a
> > lot, with UTF-8 and its ubiquity. Removing the extra complication would
> > make code a little easier to read, and reduce variability when
> > reproducing problems. But there's no hurry, of course.
> I'm not sure I understand which part do you want to remove.

The part that currently looks like this:

         (coding-system-for-read
          ;; Force the EOL conversion to be -unix, in case the files
          ;; to be compared have DOS EOLs.  In that case, EOL
          ;; conversion will produce a patch file that will either
          ;; fail to apply, or will change the EOL format of some of
          ;; the lines in the patched file.
          (coding-system-change-eol-conversion
           (if files (vc-coding-system-for-diff (car files)) 'undecided)
           'unix))

As we've established, the only part that's used in vc-root-diff (and 
only now) is binding coding-system-change-eol-conversion to 
'undecided-unix'. We could leave it there, though it doesn't seem to 
change the behavior in my tests.