Have 'vc-prepare-patch' handle prefix arguments.

* lisp/emacs-lisp/package-vc.el (package-vc-prepare-patch): Use
'vc-prepare-patch-prompt-revisions'.
* lisp/vc/vc.el (vc-prepare-patch-prompt-revisions): Extract common
function and handle prefix arguments.
(vc-prepare-patch): Pull logic out to
'vc-prepare-patch-prompt-revisions'.

1 files changed, 33 insertions, 15 deletions

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index fd59c95fc8b..adf57229986 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -3384,25 +3384,43 @@ If nil, no default will be used.  This option may be set locally."
                                (vc-root-dir))))
             :buffer (current-buffer)))))
 
+(defun vc-prepare-patch-prompt-revisions ()
+  "Prompt the user for a list revisions.
+Prepare a default value, depending on the current context.  With
+a numerical prefix argument, use the last N revisions as the
+default value.  If the current buffer is a log-view buffer, use
+the marked commits.  Otherwise fall back to the working revision
+of the current file."
+  (vc-read-multiple-revisions
+   "Revisions: " nil nil nil
+   (or (and-let* ((arg current-prefix-arg)
+                  (fs (vc-deduce-fileset t)))
+         (cl-loop with file = (caadr fs)
+                  repeat (prefix-numeric-value arg)
+                  for rev = (vc-working-revision file)
+                  then (vc-call-backend
+                        (car fs) 'previous-revision
+                        file rev)
+                  when rev collect it into revs
+                  finally return (mapconcat #'identity revs ",")))
+       (and-let* ((revs (log-view-get-marked)))
+         (mapconcat #'identity revs ","))
+       (and-let* ((file (buffer-file-name)))
+         (vc-working-revision file)))))
+
 ;;;###autoload
 (defun vc-prepare-patch (addressee subject revisions)
   "Compose an Email sending patches for REVISIONS to ADDRESSEE.
-If `vc-prepare-patches-separately' is nil, SUBJECT will be used
-as the default subject for the message (and it will be prompted
-for when called interactively).  Otherwise a separate message
-will be composed for each revision, with SUBJECT derived from the
-invidividual commits.
-
-When invoked interactively in a Log View buffer with marked
-revisions, those revisions will be used."
+If `vc-prepare-patches-separately' is nil, use SUBJECT as the
+default subject for the message, or prompt a subject when invoked
+interactively.  Otherwise compose a separate message for each
+revision, with SUBJECT derived from each revision subject.
+When invoked with a numerical prefix argument, use the last N
+revisions.
+When invoked interactively in a Log View buffer with
+marked revisions, use those these."
   (interactive
-   (let ((revs (vc-read-multiple-revisions
-                "Revisions: " nil nil nil
-                (or (and-let* ((revs (log-view-get-marked)))
-                      (mapconcat #'identity revs ","))
-                    (and-let* ((file (buffer-file-name)))
-                      (vc-working-revision file)))))
-         to)
+   (let ((revs (vc-prepare-patch-prompt-revisions)) to)
      (require 'message)
      (while (null (setq to (completing-read-multiple
                             (format-prompt