bug#37395: [PATCH v4] diff-mode.el: take into account patch separators

[Konstantin Kharlamov]

* lisp/vc/diff-mode.el (diff-prev-line-if-patch-separator):
A function to return prev. line if it has git-format-patch
separator.
(diff-end-of-hunk): Make use of
diff-prev-line-if-patch-separator
diff-buffer-type: whether a buffer is a git-diff
(define-derived-mode): set diff-buffer-type to appropriate
value
---

v4:
    * replace defsubst with defun
    * define diff-buffer-type with defvar and set with setq-local
    * call `setq-local` just once

 lisp/vc/diff-mode.el | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 19f9c802d4..1cc3cd3d4d 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -511,6 +511,19 @@ diff-hunk-style
     (goto-char (match-end 0)))
   style)
 
+(defun diff-prev-line-if-patch-separator ()
+  "Return previous line if it has patch separator as produced by git."
+  (pcase diff-buffer-type
+    ('git
+     (save-excursion
+       (let ((old-point (point)))
+         (previous-line)
+         (beginning-of-line)
+         (if (looking-at "^-- $")
+             (point)
+           old-point))))
+    (_ (point))))
+
 (defun diff-end-of-hunk (&optional style donttrustheader)
   "Advance to the end of the current hunk, and return its position."
   (let (end)
@@ -561,7 +574,8 @@ diff-end-of-hunk
         (goto-char (or end (point-max)))
         (while (eq ?\n (char-before (1- (point))))
           (forward-char -1)
-          (setq end (point)))))
+          (setq end (point))))
+      (setq end (diff-prev-line-if-patch-separator)))
     ;; The return value is used by easy-mmode-define-navigation.
     (goto-char (or end (point-max)))))
 
@@ -1425,6 +1439,7 @@ diff--font-lock-cleanup
 
 (defvar whitespace-style)
 (defvar whitespace-trailing-regexp)
+(defvar diff-buffer-type nil)
 
 ;;;###autoload
 (define-derived-mode diff-mode fundamental-mode "Diff"
@@ -1491,7 +1506,12 @@ diff-mode
   (add-function :filter-return (local 'filter-buffer-substring-function)
                 #'diff--filter-substring)
   (unless buffer-file-name
-    (hack-dir-local-variables-non-file-buffer)))
+    (hack-dir-local-variables-non-file-buffer))
+  (save-excursion
+    (setq-local diff-buffer-type
+                (if (re-search-forward "^diff --git" nil t)
+                    'git
+                  nil))))
 
 ;;;###autoload
 (define-minor-mode diff-minor-mode
-- 
2.23.0