* lisp/help-fns.el (help-C-file-name): Handle advised functions.

* lisp/emacs-lisp/find-func.el (find-function-C-source): Idem.
* lisp/emacs-lisp/nadvice.el (advice--cd*r): New function.
* help-fns.el (describe-function-1): Use it.

Fixes: debbugs:16478

lisp/emacs-lisp/find-func.el

@@ -219,7 +219,7 @@ TYPE should be nil to find a function, or `defvar' to find a variable."
 			 (regexp-quote (symbol-name fun-or-var))
 			 "\"")
 	       (concat "DEFUN[ \t\n]*([ \t\n]*\""
-		       (regexp-quote (subr-name fun-or-var))
+		       (regexp-quote (subr-name (advice--cd*r fun-or-var)))
 		       "\""))
 	     nil t)
       (error "Can't find source for %s" fun-or-var))

lisp/emacs-lisp/nadvice.el

@@ -67,6 +67,11 @@ Each element has the form (WHERE BYTECODE STACK) where:
 (defsubst advice--cdr   (f) (aref (aref f 2) 2))
 (defsubst advice--props (f) (aref (aref f 2) 3))
 
+(defun advice--cd*r (f)
+  (while (advice--p f)
+    (setq f (advice--cdr f)))
+  f)
+
 (defun advice--make-docstring (function)
   "Build the raw docstring for FUNCTION, presumably advised."
   (let ((flist (indirect-function function))