emacs-29 0c50af054f9: Fix applying patches with Git on MS-Windows

[Eli Zaretskii]

branch: emacs-29
commit 0c50af054f94313c458495524c90205fd4415bc8
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix applying patches with Git on MS-Windows
    
    * lisp/vc/vc.el (vc-diff-internal): For Git, always suppress EOL
    conversion when reading the diffs into a buffer.  Doc fix.
    * lisp/vc/vc-git.el (vc-git-checkin): Make sure to suppress EOL
    conversion when the patch file is written.  (Bug#65049)
---
 lisp/vc/vc-git.el | 10 +++++++++-
 lisp/vc/vc.el     | 21 +++++++++++++++++----
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 7ae763d2ee4..218696c05f4 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1051,7 +1051,15 @@ It is based on `log-edit-mode', and has Git-specific 
extensions."
                 (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 410fe5c01e1..db4fa76abd4 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1894,7 +1894,9 @@ in the output buffer."
     (vc-run-delayed (vc-diff-finish (current-buffer) nil))))
 
 (defun vc-diff-internal (async vc-fileset rev1 rev2 &optional verbose buffer)
-  "Report diffs between two revisions of a fileset.
+  "Report diffs between revisions REV1 and REV2 of a fileset in VC-FILESET.
+ASYNC non-nil means run the backend's commands asynchronously if possible.
+VC-FILESET should have the format described in `vc-deduce-fileset'.
 Output goes to the buffer BUFFER, which defaults to *vc-diff*.
 BUFFER, if non-nil, should be a buffer or a buffer name.
 Return t if the buffer had changes, nil otherwise."
@@ -1910,15 +1912,26 @@ Return t if the buffer had changes, nil otherwise."
         ;; but the only way to set it for each file included would
         ;; be to call the back end separately for each file.
         (coding-system-for-read
-         (if files (vc-coding-system-for-diff (car files)) 'undecided))
+          ;; 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))
          (orig-diff-buffer-clone
           (if revert-buffer-in-progress-p
               (clone-buffer
                (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 (car vc-fileset) 'Git)))
        (setq coding-system-for-read
              (coding-system-change-eol-conversion coding-system-for-read
                                                   'dos)))