feature/package+vc e092e60f15 4/9: Add a package-vc command for submitting ptches

[Philip Kaludercic]

branch: feature/package+vc
commit e092e60f1539898a42ed157b87bdd32f512109e0
Author: Philip Kaludercic <philipk@posteo.net>
Commit: Philip Kaludercic <philipk@posteo.net>

    Add a package-vc command for submitting ptches
    
    * lisp/emacs-lisp/package-vc.el (package-vc-read-pkg): Add auxiliary
    command for querying source packages.
    (package-vc-prepare-patch): Add it.
    * lisp/emacs-lisp/package.el (package-maintainers): Add an optional
    NO-ERROR argument.
---
 lisp/emacs-lisp/package-vc.el | 21 +++++++++++++++++++++
 lisp/emacs-lisp/package.el    | 17 ++++++++++-------
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/lisp/emacs-lisp/package-vc.el b/lisp/emacs-lisp/package-vc.el
index 2a45bacf6e..d3850a5e2c 100644
--- a/lisp/emacs-lisp/package-vc.el
+++ b/lisp/emacs-lisp/package-vc.el
@@ -286,5 +286,26 @@ be requested using REV."
 ;;;###autoload
 (defalias 'package-checkout #'package-vc-fetch)
 
+(defun package-vc-read-pkg (prompt)
+  "Query for a source package description with PROMPT."
+  (completing-read
+   prompt
+   package-alist
+   (lambda (pkg) (package-vc-p (cadr pkg)))
+   t))
+
+(defun package-vc-prepare-patch (pkg subject revisions)
+  "Send a patch to the maintainer of a package PKG.
+SUBJECT and REVISIONS are used passed on to `vc-prepare-patch'.
+PKG must be a package description."
+  (interactive
+   (list (package-vc-read-pkg "Package to prepare a patch for: ")
+         (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 (package-maintainers pkg t)
+                    subject revisions))
+
 (provide 'package-vc)
 ;;; package-vc.el ends here
diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 9ac94fa6bc..6e891fede1 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -4516,20 +4516,23 @@ DESC must be a `package-desc' object."
         (funcall browse-url-secondary-browser-function url)
       (browse-url url))))
 
-(defun package-maintainers (pkg-desc)
+(defun package-maintainers (pkg-desc &optional no-error)
   "Return an email address for the maintainers of PKG-DESC.
 The email address may contain commas, if there are multiple
 maintainers.  If no maintainers are found, an error will be
-thrown."
+signalled.  If the optional argument NO-ERROR is non-nil no error
+will be signalled in that case."
   (unless pkg-desc
-    (user-error "Invalid package description"))
+    (error "Invalid package description"))
   (let* ((extras (package-desc-extras pkg-desc))
          (maint (alist-get :maintainer extras)))
-    (unless maint
+    (cond
+     ((and (null maint) (null no-error))
       (user-error "Package has no explicit maintainer"))
-    (with-temp-buffer
-      (package--print-email-button maint)
-      (string-trim (substring-no-properties (buffer-string))))))
+     ((not (null maint))
+      (with-temp-buffer
+        (package--print-email-button maint)
+        (string-trim (substring-no-properties (buffer-string))))))))
 
 ;; TODO: Allow attaching a patch to send directly to the maintainer.
 ;; Ideally this should be able to detect the local changes, convert