New option to enable global-whitespace-mode in special-buffers (bug#79230)

* lisp/whitespace.el (whitespace-global-mode-buffers): New custom
option.
(whitespace-enable-predicate): Use it.
(whitespace-global-modes): Refer to the new option.

lisp/whitespace.el

@@ -904,7 +904,12 @@ of the list is negated if it begins with `not'.  For example:
    (c-mode c++-mode)
 
 means that `whitespace-mode' is turned on for buffers in C and
-C++ modes only."
+C++ modes only.
+
+Global `whitespace-mode' will not automatically turn on in internal
+buffers (with name starting from space) and special buffers (with name
+starting from \"*\"), except \"*scratch*\" buffer.  Use
+`whitespace-global-mode-buffers' to customize this behavior."
   :type '(choice :tag "Global Modes"
 		 (const :tag "None" nil)
 		 (const :tag "All" t)
@@ -914,6 +919,12 @@ C++ modes only."
 		      (repeat :inline t
 			      (symbol :tag "Mode")))))
 
+(defcustom whitespace-global-mode-buffers (list (regexp-quote "*scratch*"))
+  "Buffer name regexps where global `whitespace-mode' can be auto-enabled.
+The value is a list of regexps.  Set this custom option when you need
+`whitespace-mode' in special buffers like *Org Src*."
+  :type '(list (regexp :tag "Regexp matching buffer name"))
+  :version "31.1")
 
 (defcustom whitespace-action nil
   "Specify which action is taken when a buffer is visited or written.
@@ -1042,7 +1053,10 @@ See also `whitespace-newline' and `whitespace-display-mappings'."
          ;; ...the buffer is not special (name starts with *)
          (or (not (eq (aref (buffer-name) 0) ?*))
              ;; except the scratch buffer.
-             (string= (buffer-name) "*scratch*"))))
+             (seq-find
+              (lambda (re)
+                (string-match-p re (buffer-name)))
+              whitespace-global-mode-buffers))))
   "Predicate to decide which buffers obey `global-whitespace-mode'.
 This function is called with no argument and should return non-nil
 if the current buffer should obey `global-whitespace-mode'.