Fix minor defcustom issues in Gnus (Bug#66715)

* lisp/gnus/gnus-art.el (gnus-button-prefer-mid-or-mail): Allow
function and add :tag to const values.
* lisp/gnus/gnus-bookmark.el (gnus-bookmark-bookmark-inline-details):
Fix docstring.
* lisp/gnus/gnus-sum.el (gnus-simplify-subject-fuzzy-regexp): Allow a
single regexp as value.
* lisp/gnus/message.el (message-indent-citation-function): Allow a
single function as value.
(message-mail-alias-type): Allow for a list of options as value.
(message-dont-reply-to-names): Allow a function as value.
* lisp/gnus/spam-report.el (spam-report-url-ping-function): Fix
default value for the function widget.

lisp/gnus/gnus-art.el

@@ -1622,7 +1622,8 @@ predicate.  See Info node `(gnus)Customizing Articles'."
   "The protocol used for encrypt articles.
 It is a string, such as \"PGP\".  If nil, ask user."
   :version "22.1"
-  :type 'string
+  :type '(choice (const :tag "Ask me" nil)
+                 string)
   :group 'mime-security)
 
 (defcustom gnus-use-idna t
@@ -7553,10 +7554,11 @@ must return `mid', `mail', `invalid' or `ask'."
   :version "22.1"
   :group 'gnus-article-buttons
   :type '(choice (function-item :tag "Heuristic function"
-				gnus-button-mid-or-mail-heuristic)
-		 (const ask)
-		 (const mid)
-		 (const mail)))
+                                gnus-button-mid-or-mail-heuristic)
+                 (const :tag "Query me" ask)
+                 (const :tag "Assume it's a message ID" mid)
+                 (const :tag "Assume it's a mail address" mail)
+                 function))
 
 (defcustom gnus-button-mid-or-mail-heuristic-alist
   '((-10.0 . ".+\\$.+@")

lisp/gnus/gnus-bookmark.el

@@ -112,7 +112,7 @@ You can toggle whether details are shown with \\<gnus-bookmark-bmenu-mode-map>\\
 
 (defcustom gnus-bookmark-bookmark-inline-details '(author)
   "Details to be shown with `gnus-bookmark-bmenu-toggle-infos'.
-The default value is \(subject)."
+The default value is (author)."
   :type '(list :tag "Gnus bookmark details"
 	       (set :inline t
 		    (const :tag "Author" author)

lisp/gnus/gnus-sum.el

@@ -315,7 +315,8 @@ This can either be a regular expression or list of regular expressions
 that will be removed from subject strings if fuzzy subject
 simplification is selected."
   :group 'gnus-thread
-  :type '(repeat regexp))
+  :type '(choice regexp
+                 (repeat regexp)))
 
 (defcustom gnus-show-threads t
   "If non-nil, display threads in summary mode."

lisp/gnus/message.el

@@ -1147,7 +1147,8 @@ Note that these functions use `mail-citation-hook' if that is non-nil."
 This can also be a list of functions.  Each function can find the
 citation between (point) and (mark t).  And each function should leave
 point and mark around the citation text as modified."
-  :type 'function
+  :type '(choice function
+                 (repeat function))
   :link '(custom-manual "(message)Insertion Variables")
   :group 'message-insertion)
 
@@ -1408,8 +1409,9 @@ This can also be a list of values."
   :group 'message
   :link '(custom-manual "(message)Mail Aliases")
   :type '(choice (const :tag "Use Mailabbrev" abbrev)
-		 (const :tag "Use ecomplete" ecomplete)
-		 (const :tag "No expansion" nil)))
+                 (const :tag "Use ecomplete" ecomplete)
+                 (set (const :tag "Use Mailabbrev" abbrev)
+                      (const :tag "Use ecomplete" ecomplete))))
 
 (defcustom message-self-insert-commands '(self-insert-command)
   "List of `self-insert-command's used to trigger ecomplete.
@@ -1453,8 +1455,9 @@ If a function email is passed as the argument."
   :group 'message
   :link '(custom-manual "(message)Wide Reply")
   :type '(choice (const :tag "Yourself" nil)
-		 regexp
-		 (repeat :tag "Regexp List" regexp)))
+                 regexp
+                 (repeat :tag "Regexp List" regexp)
+                 function))
 
 (defsubst message-dont-reply-to-names ()
   (if (functionp message-dont-reply-to-names)

lisp/gnus/spam-report.el

@@ -64,7 +64,7 @@ The function must accept the arguments `host' and `report'."
 		 spam-report-url-ping-mm-url)
 	  (const :tag "Store request URLs in `spam-report-requests-file'"
 		 spam-report-url-to-file)
-	  (function :tag "User defined function" nil)))
+	  (function :tag "User defined function")))
 
 (defcustom spam-report-requests-file
   (nnheader-concat gnus-directory "spam/" "spam-report-requests.url")