Arrange to load nadvice later in loadup.el

This is done simply so as to avoid scattering nadvice's code into
`simple.el` and `cl-print.el`.

* lisp/loadup.el ("emacs-lisp/nadvice"): Move down after "simple".

* lisp/help.el (help-command-error-confusable-suggestions): Make it
call `command-error-default`.
(command-error-function): Replace the top-level call to `add-function`
with a simple `setq` since `add-function` is not available at this
stage any more.

* lisp/emacs-lisp/nadvice.el (interactive-form) <advice>:
(cl-print-object) <advice>: Rename from `advice--get-interactive-form`
and `advice--cl-print-object`.

* lisp/emacs-lisp/cl-print.el (cl-print-object) <advice>:
* lisp/simple.el (interactive-form) <advice>: Move to `nadvice.el`.
(pre-redisplay-function): Replace the top-level call to `add-function`
with a simple `setq` since `add-function` is not available at this
stage any more.

* lisp/emacs-lisp/cl-generic.el: Use `oclosure-object` instead of `advice`
as representative of the OClosure specializers to prefill the dispatcher table.

lisp/emacs-lisp/cl-generic.el

@@ -1313,7 +1313,7 @@ Used internally for the (major-mode MODE) context specializers."
             (list cl-generic--oclosure-generalizer))))
    (cl-call-next-method)))
 
-(cl--generic-prefill-dispatchers 0 advice)
+(cl--generic-prefill-dispatchers 0 oclosure-object)
 
 ;;; Support for unloading.
 

lisp/emacs-lisp/cl-print.el

@@ -221,14 +221,8 @@ into a button whose action shows the function's disassembly.")
                             'byte-code-function object)))))
   (princ ")" stream))
 
-;; This belongs in nadvice.el, of course, but some load-ordering issues make it
-;; complicated: cl-generic uses macros from cl-macs and cl-macs uses advice-add
-;; from nadvice, so nadvice needs to be loaded before cl-generic and hence
-;; can't use cl-defmethod.
-(cl-defmethod cl-print-object ((object advice) stream)
-  ;; FIXME: η-reduce!
-  (advice--cl-print-object object stream))
-
+;; This belongs in oclosure.el, of course, but some load-ordering issues make it
+;; complicated.
 (cl-defmethod cl-print-object ((object accessor) stream)
   ;; FIXME: η-reduce!
   (oclosure--accessor-cl-print object stream))

lisp/emacs-lisp/nadvice.el

@@ -178,14 +178,13 @@ function of type `advice'.")
       (cadr (or iff ifm)))))
 
 
-;; This is the `advice' method of `interactive-form'.
-(defun advice--get-interactive-form (ad)
+(cl-defmethod interactive-form ((ad advice) &optional _)
   (let ((car (advice--car ad))
         (cdr (advice--cdr ad)))
     (when (or (commandp car) (commandp cdr))
       `(interactive ,(advice--make-interactive-form car cdr)))))
 
-(defun advice--cl-print-object (object stream)
+(cl-defmethod cl-print-object ((object advice) stream)
   (cl-assert (advice--p object))
   (princ "#f(advice " stream)
   (cl-print-object (advice--car object) stream)

lisp/help.el

@@ -2094,7 +2094,10 @@ the suggested string to use instead.  See
                   confusables ", ")
        string))))
 
-(defun help-command-error-confusable-suggestions (data _context _signal)
+(defun help-command-error-confusable-suggestions (data context signal)
+  ;; Delegate most of the work to the original default value of
+  ;; `command-error-function' implemented in C.
+  (command-error-default-function data context signal)
   (pcase data
     (`(void-variable ,var)
      (let ((suggestions (help-uni-confusable-suggestions
@@ -2103,8 +2106,10 @@ the suggested string to use instead.  See
          (princ (concat "\n  " suggestions) t))))
     (_ nil)))
 
-(add-function :after command-error-function
-              #'help-command-error-confusable-suggestions)
+(when (eq command-error-function #'command-error-default-function)
+  ;; Override the default set in the C code.
+  (setq command-error-function
+        #'help-command-error-confusable-suggestions))
 
 (define-obsolete-function-alias 'help-for-help-internal #'help-for-help "28.1")
 

lisp/loadup.el

@@ -197,7 +197,6 @@
 (load "button")                  ;After loaddefs, because of define-minor-mode!
 (load "emacs-lisp/cl-preloaded")
 (load "emacs-lisp/oclosure")          ;Used by cl-generic and nadvice
-(load "emacs-lisp/nadvice")
 (load "obarray")        ;abbrev.el is implemented in terms of obarrays.
 (load "abbrev")         ;lisp-mode.el and simple.el use define-abbrev-table.
 (load "help")
@@ -250,6 +249,7 @@
   ;; A particularly demanding file to load; 1600 does not seem to be enough.
   (load "emacs-lisp/cl-generic"))
 (load "simple")
+(load "emacs-lisp/nadvice")
 (load "minibuffer") ;Needs cl-generic (and define-minor-mode).
 (load "frame")
 (load "startup")

lisp/simple.el

@@ -2384,12 +2384,6 @@ ORIGINAL-NAME is used internally only."
          spec)))
     (_ (internal--interactive-form cmd))))
 
-(cl-defmethod interactive-form ((function advice) &optional _)
-  ;; This should ideally be in `nadvice.el' but `nadvice.el' is loaded before
-  ;; `cl-generic.el' so it can't use `cl-defmethod'.
-  ;; FIXME: η-reduce!
-  (advice--get-interactive-form function))
-
 (defun command-execute (cmd &optional record-flag keys special)
   ;; BEWARE: Called directly from the C code.
   "Execute CMD as an editor command.
@@ -6551,9 +6545,9 @@ is set to the buffer displayed in that window.")
         (with-current-buffer (window-buffer win)
           (run-hook-with-args 'pre-redisplay-functions win))))))
 
-(add-function :before pre-redisplay-function
-              #'redisplay--pre-redisplay-functions)
-
+(when (eq pre-redisplay-function #'ignore)
+  ;; Override the default set in the C code.
+  (setq pre-redisplay-function #'redisplay--pre-redisplay-functions))
 
 (defvar-local mark-ring nil
   "The list of former marks of the current buffer, most recent first.")