bug#65049: Minor update to the repro steps

[Eli Zaretskii <eliz@gnu.org>]

> From: Maxim Kim <habamax@gmail.com>
> Cc: juri@linkov.net,  65049@debbugs.gnu.org
> Date: Wed, 23 Aug 2023 14:28:10 +1000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> So, it works for the repo with files having windows CRLF.
> And doesn't work if the file has EOL type: LF.

Thanks, this finally allowed me to nail the sucker.  The fix is a bit
more complex than I thought, because this bug has two parts: one of
them in "C-x v D", the other in vc-git-checkin.  The patch is below;
please give it a try with all your real-life use cases.

Dmitry, do you see any problems with installing this on the release
branch?  Or do you prefer to keep it on master for a while, and then
backport if no one complains?

diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 7ae763d..218696c 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1051,7 +1051,15 @@ vc-git-checkin
                 (user-error "Index not empty"))
               (setq pos (point))))))
       (unless (string-empty-p vc-git-patch-string)
-        (let ((patch-file (make-nearby-temp-file "git-patch")))
+        (let ((patch-file (make-nearby-temp-file "git-patch"))
+              ;; Temporarily countermand the let-binding at the
+              ;; beginning of this function.
+              (coding-system-for-write
+               (coding-system-change-eol-conversion
+                ;; On DOS/Windows, it is important for the patch file
+                ;; to have the Unix EOL format, because Git expects
+                ;; that, even on Windows.
+                (or pcsw vc-git-commits-coding-system) 'unix)))
           (with-temp-file patch-file
             (insert vc-git-patch-string))
           (unwind-protect
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 410fe5c..4e008de 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1917,8 +1917,12 @@ vc-diff-internal
                (generate-new-buffer-name " *vc-diff-clone*") nil))))
     ;; On MS-Windows and MS-DOS, Diff is likely to produce DOS-style
     ;; EOLs, which will look ugly if (car files) happens to have Unix
-    ;; EOLs.
-    (if (memq system-type '(windows-nt ms-dos))
+    ;; EOLs.  But for Git, we must force Unix EOLs in the diffs, since
+    ;; Git always produces Unix EOLs in the parts that didn't come
+    ;; from the file, and wants to see any CR characters when applying
+    ;; patches.
+    (if (and (memq system-type '(windows-nt ms-dos))
+             (not (eq (vc-deduce-backend) 'Git)))
 	(setq coding-system-for-read
 	      (coding-system-change-eol-conversion coding-system-for-read
 						   'dos)))