>From 724b85acd34e4e5dd6e8cb521eb03eda08ff105a Mon Sep 17 00:00:00 2001
From: Philip Kaludercic <philipk@posteo.net>
Date: Sun, 13 Nov 2022 17:05:20 +0100
Subject: [PATCH] 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'.
---
 lisp/emacs-lisp/package-vc.el | 14 ++++++------
 lisp/vc/vc.el                 | 40 +++++++++++++++++++++++++----------
 2 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/lisp/emacs-lisp/package-vc.el b/lisp/emacs-lisp/package-vc.el
index 664629d156..37ef35edad 100644
--- a/lisp/emacs-lisp/package-vc.el
+++ b/lisp/emacs-lisp/package-vc.el
@@ -733,17 +733,17 @@ package-vc-rebuild
 ;;;###autoload
 (defun package-vc-prepare-patch (pkg subject revisions)
   "Send patch for REVISIONS to maintainer of the package PKG using SUBJECT.
-SUBJECT and REVISIONS are passed on to `vc-prepare-patch', which see.
-PKG must be a package description.
-Interactively, prompt for PKG, SUBJECT, and REVISIONS.  However,
-if the current buffer has marked commit log entries, REVISIONS
-are the tags of the marked entries, see `log-view-get-marked'."
+SUBJECT and REVISIONS are passed on to `vc-prepare-patch', which
+see.  PKG must be a package description.  Interactively, prompt
+for PKG, SUBJECT, and REVISIONS.  When invoked with a numerical
+prefix argument, the last N revisions will be used.  When invoked
+interactively in a Log View buffer with marked revisions, those
+revisions will be used."
   (interactive
    (list (package-vc--read-package-desc "Package to prepare a patch for: " t)
          (and (not vc-prepare-patches-separately)
               (read-string "Subject: " "[PATCH] " nil nil t))
-         (or (log-view-get-marked)
-             (vc-read-multiple-revisions "Revisions: "))))
+         (vc-prepare-patch-prompt-revisions)))
   (vc-prepare-patch (package-maintainers pkg t)
                     subject revisions))
 
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 513fbb23fe..f49f5d3307 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -3384,6 +3384,30 @@ vc-default-prepare-patch
                                (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.
@@ -3391,18 +3415,12 @@ vc-prepare-patch
 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."
+invidividual commits.  When invoked with a numerical prefix
+argument, the last N revisions will be used.  When invoked
+interactively in a Log View buffer with marked revisions, those
+revisions will be used."
   (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
-- 
2.35.1