Generalize the prefix-command machinery of C-u

* lisp/simple.el (prefix-command-echo-keystrokes-functions)
(prefix-command-preserve-state-hook): New hooks.
(internal-echo-keystrokes-prefix): New function.
(prefix-command--needs-update, prefix-command--last-echo): New vars.
(prefix-command-update, prefix-command-preserve): New functions.
(reset-this-command-lengths): New compatibility definition.
(universal-argument--mode): Call prefix-command-update.
(universal-argument, universal-argument-more, negative-argument)
(digit-argument): Call prefix-command-preserve-state.

* src/keyboard.c: Call internal-echo-keystrokes-prefix to build
the "prefix argument" to echo.
(this_command_key_count_reset, before_command_key_count)
(before_command_echo_length): Delete variables.
(echo_add_key): Always add a space.
(echo_char): Remove.
(echo_dash): Don't give up when this_command_key_count is 0, since that
is now the case after a prefix command.
(echo_update): New function, extracted from echo_now.
(echo_now): Use it.
(add_command_key, read_char, record_menu_key): Remove old disabled code.
(command_loop_1): Don't refrain from pushing an undo boundary when
prefix-arg is set.  Remove other prefix-arg special case, now handled
directly in the prefix commands instead.  But call echo_now if there's
a prefix state to echo.
(read_char, record_menu_key): Use echo_update instead of echo_char.
(read_key_sequence): Use echo_now rather than echo_dash/echo_char.
(Freset_this_command_lengths): Delete function.
(syms_of_keyboard): Define Qinternal_echo_keystrokes_prefix.
(syms_of_keyboard): Don't defsubr Sreset_this_command_lengths.

* lisp/simple.el: Use those new hooks for C-u.
(universal-argument--description): New function.
(prefix-command-echo-keystrokes-functions): Use it.
(universal-argument--preserve): New function.
(prefix-command-preserve-state-hook): Use it.
(command-execute): Call prefix-command-update if needed.

* lisp/kmacro.el (kmacro-step-edit-prefix-commands)
(kmacro-step-edit-prefix-index): Delete variables.
(kmacro-step-edit-query, kmacro-step-edit-insert): Remove ad-hoc
support for prefix arg commands.
(kmacro-step-edit-macro): Don't bind kmacro-step-edit-prefix-index.

* lisp/emulation/cua-base.el (cua--prefix-override-replay)
(cua--shift-control-prefix): Use prefix-command-preserve-state.
Remove now unused arg `arg'.
(cua--prefix-override-handler, cua--prefix-repeat-handler)
(cua--shift-control-c-prefix, cua--shift-control-x-prefix):
Update accordingly.
(cua--prefix-override-timeout): Don't call reset-this-command-lengths
any more.
(cua--keep-active, cua-exchange-point-and-mark): Don't set mark-active
if the mark is not set.

3 files changed, 117 insertions, 66 deletions

diff --git a/lisp/emulation/cua-base.el b/lisp/emulation/cua-base.el
index e91ce80bbe2..52e1647ede7 100644
--- a/lisp/emulation/cua-base.el
+++ b/lisp/emulation/cua-base.el
@@ -685,7 +685,7 @@ a cons (TYPE . COLOR), then both properties are affected."
 (defvar cua--prefix-override-timer nil)
 (defvar cua--prefix-override-length nil)
 
-(defun cua--prefix-override-replay (arg repeat)
+(defun cua--prefix-override-replay (repeat)
   (let* ((keys (this-command-keys))
          (i (length keys))
          (key (aref keys (1- i))))
@@ -705,21 +705,23 @@ a cons (TYPE . COLOR), then both properties are affected."
     ;; Don't record this command
     (setq this-command last-command)
     ;; Restore the prefix arg
-    (setq prefix-arg arg)
-    (reset-this-command-lengths)
+    ;; This should make it so that exchange-point-and-mark gets the prefix when
+    ;; you do C-u C-x C-x C-x work (where the C-u is properly passed to the C-x
+    ;; C-x binding after the first C-x C-x was rewritten to just C-x).
+    (prefix-command-preserve-state)
     ;; Push the key back on the event queue
     (setq unread-command-events (cons key unread-command-events))))
 
-(defun cua--prefix-override-handler (arg)
+(defun cua--prefix-override-handler ()
   "Start timer waiting for prefix key to be followed by another key.
 Repeating prefix key when region is active works as a single prefix key."
-  (interactive "P")
-  (cua--prefix-override-replay arg 0))
+  (interactive)
+  (cua--prefix-override-replay 0))
 
-(defun cua--prefix-repeat-handler (arg)
+(defun cua--prefix-repeat-handler ()
   "Repeating prefix key when region is active works as a single prefix key."
-  (interactive "P")
-  (cua--prefix-override-replay arg 1))
+  (interactive)
+  (cua--prefix-override-replay 1))
 
 (defun cua--prefix-copy-handler (arg)
   "Copy region/rectangle, then replay last key."
@@ -742,7 +744,8 @@ Repeating prefix key when region is active works as a single prefix key."
   (when (= (length (this-command-keys)) cua--prefix-override-length)
     (setq unread-command-events (cons 'timeout unread-command-events))
     (if prefix-arg
-      (reset-this-command-lengths)
+        nil
+      ;; FIXME: Why?
       (setq overriding-terminal-local-map nil))
     (cua--select-keymaps)))
 
@@ -755,8 +758,9 @@ Repeating prefix key when region is active works as a single prefix key."
   (call-interactively this-command))
 
 (defun cua--keep-active ()
-  (setq mark-active t
-        deactivate-mark nil))
+  (when (mark t)
+    (setq mark-active t
+          deactivate-mark nil)))
 
 (defun cua--deactivate (&optional now)
   (if (not now)
@@ -944,7 +948,7 @@ See also `exchange-point-and-mark'."
   (cond ((null cua-enable-cua-keys)
          (exchange-point-and-mark arg))
         (arg
-         (setq mark-active t))
+         (when (mark t) (setq mark-active t)))
         (t
          (let (mark-active)
            (exchange-point-and-mark)
@@ -1212,25 +1216,28 @@ If ARG is the atom `-', scroll upward by nearly full screen."
 
 (defvar cua--keymaps-initialized nil)
 
-(defun cua--shift-control-prefix (prefix arg)
+(defun cua--shift-control-prefix (prefix)
   ;; handle S-C-x and S-C-c by emulating the fast double prefix function.
   ;; Don't record this command
   (setq this-command last-command)
   ;; Restore the prefix arg
-  (setq prefix-arg arg)
-  (reset-this-command-lengths)
+  ;; This should make it so that exchange-point-and-mark gets the prefix when
+  ;; you do C-u S-C-x C-x work (where the C-u is properly passed to the C-x
+  ;; C-x binding after the first S-C-x was rewritten to just C-x).
+  (prefix-command-preserve-state)
   ;; Activate the cua--prefix-repeat-keymap
   (setq cua--prefix-override-timer 'shift)
   ;; Push duplicate keys back on the event queue
-  (setq unread-command-events (cons prefix (cons prefix unread-command-events))))
+  (setq unread-command-events
+        (cons prefix (cons prefix unread-command-events))))
 
-(defun cua--shift-control-c-prefix (arg)
-  (interactive "P")
-  (cua--shift-control-prefix ?\C-c arg))
+(defun cua--shift-control-c-prefix ()
+  (interactive)
+  (cua--shift-control-prefix ?\C-c))
 
-(defun cua--shift-control-x-prefix (arg)
-  (interactive "P")
-  (cua--shift-control-prefix ?\C-x arg))
+(defun cua--shift-control-x-prefix ()
+  (interactive)
+  (cua--shift-control-prefix ?\C-x))
 
 (defun cua--init-keymaps ()
   ;; Cache actual rectangle modifier key.
diff --git a/lisp/kmacro.el b/lisp/kmacro.el
index 9636a36b1e2..ddf3005bab5 100644
--- a/lisp/kmacro.el
+++ b/lisp/kmacro.el
@@ -941,7 +941,6 @@ without repeating the prefix."
 (defvar kmacro-step-edit-inserting)      ;; inserting into macro
 (defvar kmacro-step-edit-appending)      ;; append to end of macro
 (defvar kmacro-step-edit-replace)        ;; replace orig macro when done
-(defvar kmacro-step-edit-prefix-index)   ;; index of first prefix arg key
 (defvar kmacro-step-edit-key-index)      ;; index of current key
 (defvar kmacro-step-edit-action)         ;; automatic action on next pre-command hook
 (defvar kmacro-step-edit-help)           ;; kmacro step edit help enabled
@@ -976,11 +975,6 @@ This keymap is an extension to the `query-replace-map', allowing the
 following additional answers: `insert', `insert-1', `replace', `replace-1',
 `append', `append-end', `act-repeat', `skip-end', `skip-keep'.")
 
-(defvar kmacro-step-edit-prefix-commands
-  '(universal-argument universal-argument-more universal-argument-minus
-                       digit-argument negative-argument)
-  "Commands which build up a prefix arg for the current command.")
-
 (defun kmacro-step-edit-prompt (macro index)
   ;; Show step-edit prompt
   (let ((keys (and (not kmacro-step-edit-appending)
@@ -1084,21 +1078,13 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
       ;; Handle prefix arg, or query user
       (cond
        (act act) ;; set above
-       ((memq this-command kmacro-step-edit-prefix-commands)
-        (unless kmacro-step-edit-prefix-index
-          (setq kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
-        (setq act 'universal-argument))
-       ((eq this-command 'universal-argument-other-key)
-        (setq act 'universal-argument))
        (t
-        (kmacro-step-edit-prompt macro (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
+        (kmacro-step-edit-prompt macro kmacro-step-edit-key-index)
         (setq act (lookup-key kmacro-step-edit-map
                               (vector (with-current-buffer (current-buffer) (read-event))))))))
 
     ;; Resume macro execution and perform the action
     (cond
-     ((eq act 'universal-argument)
-      nil)
      ((cond
        ((eq act 'act)
         t)
@@ -1110,7 +1096,6 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
         (setq kmacro-step-edit-active 'ignore)
         nil)
        ((eq act 'skip)
-        (setq kmacro-step-edit-prefix-index nil)
         nil)
        ((eq act 'skip-keep)
         (setq this-command 'ignore)
@@ -1123,12 +1108,11 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
         (setq act t)
         t)
        ((member act '(insert-1 insert))
-        (setq executing-kbd-macro-index (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
+        (setq executing-kbd-macro-index kmacro-step-edit-key-index)
         (setq kmacro-step-edit-inserting (if (eq act 'insert-1) 1 t))
         nil)
        ((member act '(replace-1 replace))
         (setq kmacro-step-edit-inserting (if (eq act 'replace-1) 1 t))
-        (setq kmacro-step-edit-prefix-index nil)
         (if (= executing-kbd-macro-index (length executing-kbd-macro))
             (setq executing-kbd-macro (vconcat executing-kbd-macro [nil])
                   kmacro-step-edit-appending t))
@@ -1148,19 +1132,19 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
         (setq act t)
         t)
        ((eq act 'help)
-        (setq executing-kbd-macro-index (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
+        (setq executing-kbd-macro-index kmacro-step-edit-key-index)
         (setq kmacro-step-edit-help (not kmacro-step-edit-help))
         nil)
        (t ;; Ignore unknown responses
-        (setq executing-kbd-macro-index (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
+        (setq executing-kbd-macro-index kmacro-step-edit-key-index)
         nil))
-      (if (> executing-kbd-macro-index (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index))
+      (if (> executing-kbd-macro-index kmacro-step-edit-key-index)
           (setq kmacro-step-edit-new-macro
                 (vconcat kmacro-step-edit-new-macro
                          (substring executing-kbd-macro
-                                    (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index)
-                                    (if (eq act t) nil executing-kbd-macro-index)))
-                kmacro-step-edit-prefix-index nil))
+                                    kmacro-step-edit-key-index
+                                    (if (eq act t) nil
+                                      executing-kbd-macro-index)))))
       (if restore-index
           (setq executing-kbd-macro-index restore-index)))
      (t
@@ -1175,12 +1159,10 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
         (executing-kbd-macro nil)
         (defining-kbd-macro nil)
         cmd keys next-index)
-    (setq executing-kbd-macro-index (or kmacro-step-edit-prefix-index kmacro-step-edit-key-index)
-          kmacro-step-edit-prefix-index nil)
+    (setq executing-kbd-macro-index kmacro-step-edit-key-index)
     (kmacro-step-edit-prompt macro nil)
     ;; Now, we have read a key sequence from the macro, but we don't want
     ;; to execute it yet.  So push it back and read another sequence.
-    (reset-this-command-lengths)
     (setq keys (read-key-sequence nil nil nil nil t))
     (setq cmd (key-binding keys t nil))
     (if (cond
@@ -1201,25 +1183,12 @@ following additional answers: `insert', `insert-1', `replace', `replace-1',
                     unread-command-events nil)))
           (setq cmd 'ignore)
           nil)
-         ((memq cmd kmacro-step-edit-prefix-commands)
-          (reset-this-command-lengths)
-          nil)
-         ((eq cmd 'universal-argument-other-key)
-          (setq kmacro-step-edit-action t)
-          (reset-this-command-lengths)
-          (if (numberp kmacro-step-edit-inserting)
-              (setq kmacro-step-edit-inserting nil))
-          nil)
          ((numberp kmacro-step-edit-inserting)
           (setq kmacro-step-edit-inserting nil)
           nil)
          ((equal keys "\C-j")
           (setq kmacro-step-edit-inserting nil)
           (setq kmacro-step-edit-action nil)
-          ;; Forget any (partial) prefix arg from next command
-          (setq kmacro-step-edit-prefix-index nil)
-          (reset-this-command-lengths)
-          (setq overriding-terminal-local-map nil)
           (setq next-index kmacro-step-edit-key-index)
           t)
          (t nil))
@@ -1278,7 +1247,6 @@ To customize possible responses, change the \"bindings\" in `kmacro-step-edit-ma
         (kmacro-step-edit-inserting nil)
         (kmacro-step-edit-appending nil)
         (kmacro-step-edit-replace t)
-        (kmacro-step-edit-prefix-index nil)
         (kmacro-step-edit-key-index 0)
         (kmacro-step-edit-action nil)
         (kmacro-step-edit-help nil)
diff --git a/lisp/simple.el b/lisp/simple.el
index 6f76d755292..b8d4e741775 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -1711,9 +1711,13 @@ The argument SPECIAL, if non-nil, means that this command is executing
 a special event, so ignore the prefix argument and don't clear it."
   (setq debug-on-next-call nil)
   (let ((prefixarg (unless special
+                     ;; FIXME: This should probably be done around
+                     ;; pre-command-hook rather than here!
                      (prog1 prefix-arg
                        (setq current-prefix-arg prefix-arg)
-                       (setq prefix-arg nil)))))
+                       (setq prefix-arg nil)
+                       (when current-prefix-arg
+                         (prefix-command-update))))))
     (if (and (symbolp cmd)
              (get cmd 'disabled)
              disabled-command-function)
@@ -3626,6 +3630,73 @@ see other processes running on the system, use `list-system-processes'."
   (display-buffer buffer)
   nil)
 
+;;;; Prefix commands
+
+(setq prefix-command--needs-update nil)
+(setq prefix-command--last-echo nil)
+
+(defun internal-echo-keystrokes-prefix ()
+  ;; BEWARE: Called directly from the C code.
+  (if (not prefix-command--needs-update)
+      prefix-command--last-echo
+    (setq prefix-command--last-echo
+          (let ((strs nil))
+            (run-hook-wrapped 'prefix-command-echo-keystrokes-functions
+                              (lambda (fun) (push (funcall fun) strs)))
+            (setq strs (delq nil strs))
+            (when strs (mapconcat #'identity strs " "))))))
+
+(defvar prefix-command-echo-keystrokes-functions nil
+  "Abnormal hook which constructs the description of the current prefix state.
+Each function is called with no argument, should return a string or nil.")
+
+(defun prefix-command-update ()
+  "Update state of prefix commands.
+Call it whenever you change the \"prefix command state\"."
+  (setq prefix-command--needs-update t))
+
+(defvar prefix-command-preserve-state-hook nil
+  "Normal hook run when a command needs to preserve the prefix.")
+
+(defun prefix-command-preserve-state ()
+  "Pass the current prefix command state to the next command.
+Should be called by all prefix commands.
+Runs `prefix-command-preserve-state-hook'."
+  (run-hooks 'prefix-command-preserve-state-hook)
+  ;; If the current command is a prefix command, we don't want the next (real)
+  ;; command to have `last-command' set to, say, `universal-argument'.
+  (setq this-command last-command)
+  (setq real-this-command real-last-command)
+  (prefix-command-update))
+
+(defun reset-this-command-lengths ()
+  (declare (obsolete prefix-command-preserve-state "25.1"))
+  nil)
+
+;;;;; The main prefix command.
+
+;; FIXME: Declaration of `prefix-arg' should be moved here!?
+
+(add-hook 'prefix-command-echo-keystrokes-functions
+          #'universal-argument--description)
+(defun universal-argument--description ()
+  (when prefix-arg
+    (concat "C-u"
+            (pcase prefix-arg
+              (`(-) " -")
+              (`(,(and (pred integerp) n))
+               (let ((str ""))
+                 (while (and (> n 4) (= (mod n 4) 0))
+                   (setq str (concat str " C-u"))
+                   (setq n (/ n 4)))
+                 (if (= n 4) str (format " %s" prefix-arg))))
+              (_ (format " %s" prefix-arg))))))
+
+(add-hook 'prefix-command-preserve-state-hook
+          #'universal-argument--preserve)
+(defun universal-argument--preserve ()
+  (setq prefix-arg current-prefix-arg))
+
 (defvar universal-argument-map
   (let ((map (make-sparse-keymap))
         (universal-argument-minus
@@ -3664,7 +3735,8 @@ see other processes running on the system, use `list-system-processes'."
   "Keymap used while processing \\[universal-argument].")
 
 (defun universal-argument--mode ()
-  (set-transient-map universal-argument-map))
+  (prefix-command-update)
+  (set-transient-map universal-argument-map nil))
 
 (defun universal-argument ()
   "Begin a numeric argument for the following command.
@@ -3677,6 +3749,7 @@ For some commands, just \\[universal-argument] by itself serves as a flag
 which is different in effect from any particular numeric argument.
 These commands include \\[set-mark-command] and \\[start-kbd-macro]."
   (interactive)
+  (prefix-command-preserve-state)
   (setq prefix-arg (list 4))
   (universal-argument--mode))
 
@@ -3684,6 +3757,7 @@ These commands include \\[set-mark-command] and \\[start-kbd-macro]."
   ;; A subsequent C-u means to multiply the factor by 4 if we've typed
   ;; nothing but C-u's; otherwise it means to terminate the prefix arg.
   (interactive "P")
+  (prefix-command-preserve-state)
   (setq prefix-arg (if (consp arg)
                        (list (* 4 (car arg)))
                      (if (eq arg '-)
@@ -3695,6 +3769,7 @@ These commands include \\[set-mark-command] and \\[start-kbd-macro]."
   "Begin a negative numeric argument for the next command.
 \\[universal-argument] following digits or minus sign ends the argument."
   (interactive "P")
+  (prefix-command-preserve-state)
   (setq prefix-arg (cond ((integerp arg) (- arg))
                          ((eq arg '-) nil)
                          (t '-)))
@@ -3704,6 +3779,7 @@ These commands include \\[set-mark-command] and \\[start-kbd-macro]."
   "Part of the numeric argument for the next command.
 \\[universal-argument] following digits or minus sign ends the argument."
   (interactive "P")
+  (prefix-command-preserve-state)
   (let* ((char (if (integerp last-command-event)
                    last-command-event
                  (get last-command-event 'ascii-character)))