cl-generic: Fix `advertised-calling-convention` declarations

* lisp/emacs-lisp/cl-generic.el (cl-generic-define-method):
Preserve the `advertised-calling-convention`, if any (bug#58563).

* lisp/subr.el (declare): Warn when we hit this.

* lisp/emacs-lisp/byte-run.el (get-advertised-calling-convention): New fun.
* lisp/progmodes/elisp-mode.el (elisp-get-fnsym-args-string):
* lisp/help-fns.el (help-fns--signature):
* lisp/emacs-lisp/bytecomp.el (byte-compile-fdefinition): Use it.

* test/lisp/emacs-lisp/cl-generic-tests.el (cl-generic-tests--acc): New fun.
(cl-generic-tests--advertised-calling-convention-bug58563): New test.

3 files changed, 15 insertions, 6 deletions

diff --git a/lisp/emacs-lisp/byte-run.el b/lisp/emacs-lisp/byte-run.el
index 9db84c31b88..a33808ab92d 100644
--- a/lisp/emacs-lisp/byte-run.el
+++ b/lisp/emacs-lisp/byte-run.el
@@ -481,6 +481,11 @@ convention was modified."
   (puthash (indirect-function function) signature
            advertised-signature-table))
 
+(defun get-advertised-calling-convention (function)
+  "Get the advertised SIGNATURE of FUNCTION.
+Return t if there isn't any."
+  (gethash function advertised-signature-table t))
+
 (defun make-obsolete (obsolete-name current-name when)
   "Make the byte-compiler warn that function OBSOLETE-NAME is obsolete.
 OBSOLETE-NAME should be a function name or macro name (a symbol).
diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 74ba8984f29..3ceb5da804f 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -1405,11 +1405,11 @@ when printing the error message."
 			  (and (not macro-p)
 			       (compiled-function-p (symbol-function fn)))))
 	    (setq fn (symbol-function fn)))
-          (let ((advertised (gethash (if (and (symbolp fn) (fboundp fn))
-                                         ;; Could be a subr.
-                                         (symbol-function fn)
-                                       fn)
-                                     advertised-signature-table t)))
+          (let ((advertised (get-advertised-calling-convention
+                             (if (and (symbolp fn) (fboundp fn))
+                                 ;; Could be a subr.
+                                 (symbol-function fn)
+                               fn))))
             (cond
              ((listp advertised)
               (if macro-p
diff --git a/lisp/emacs-lisp/cl-generic.el b/lisp/emacs-lisp/cl-generic.el
index b3ade3b8943..7b6d43e572b 100644
--- a/lisp/emacs-lisp/cl-generic.el
+++ b/lisp/emacs-lisp/cl-generic.el
@@ -650,13 +650,17 @@ The set of acceptable TYPEs (also called \"specializers\") is defined
                                      (cl--generic-name generic)
                                      qualifiers specializers))
                   current-load-list :test #'equal)
-      (let (;; Prevent `defalias' from recording this as the definition site of
+      (let ((old-adv-cc (get-advertised-calling-convention
+                         (symbol-function sym)))
+            ;; Prevent `defalias' from recording this as the definition site of
             ;; the generic function.
             current-load-list
             ;; BEWARE!  Don't purify this function definition, since that leads
             ;; to memory corruption if the hash-tables it holds are modified
             ;; (the GC doesn't trace those pointers).
             (purify-flag nil))
+        (when (listp old-adv-cc)
+          (set-advertised-calling-convention gfun old-adv-cc nil))
         ;; But do use `defalias', so that it interacts properly with nadvice,
         ;; e.g. for tracing/debug-on-entry.
         (defalias sym gfun)))))