Avoid generating invalid usage info for pathological function

Fixes: debbugs:19645

* lisp/help.el (help-make-usage): Don't turn a "_" arg into an empty-string.
* lisp/emacs-lisp/cl-generic.el (cl--generic-lambda): Don't confuse a string
body with a docstring.

lisp/ChangeLog

@@ -1,3 +1,10 @@
+2015-01-22  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* help.el (help-make-usage): Don't turn a "_" arg into an empty-string
+	arg (bug#19645).
+	* emacs-lisp/cl-generic.el (cl--generic-lambda): Don't confuse a string
+	body with a docstring.
+
 2015-01-22  Dmitry Gutov  <dgutov@yandex.ru>
 
 	* progmodes/xref.el (xref-location-marker, xref-location-group):

lisp/emacs-lisp/cl-generic.el

@@ -228,7 +228,8 @@ This macro can only be used within the lexical scope of a cl-generic method."
     "Make the lambda expression for a method with ARGS and BODY."
     (let ((plain-args ())
           (specializers nil)
-          (doc-string (if (stringp (car-safe body)) (pop body)))
+          (doc-string (if (and (stringp (car-safe body)) (cdr body))
+                          (pop body)))
           (mandatory t))
       (dolist (arg args)
         (push (pcase arg
@@ -252,7 +253,7 @@ This macro can only be used within the lexical scope of a cl-generic method."
           ;; destructuring args, `declare' and whatnot).
           (pcase (macroexpand fun macroenv)
             (`#'(lambda ,args . ,body)
-             (let* ((doc-string (and doc-string (stringp (car body))
+             (let* ((doc-string (and doc-string (stringp (car body)) (cdr body)
                                      (pop body)))
                     (cnm (make-symbol "cl--cnm"))
                     (nmp (make-symbol "cl--nmp"))

lisp/help.el

@@ -1445,7 +1445,7 @@ the same names as used in the original source code, when possible."
 		    (let ((name (symbol-name arg)))
 		      (cond
                        ((string-match "\\`&" name) arg)
-                       ((string-match "\\`_" name)
+                       ((string-match "\\`_." name)
                         (intern (upcase (substring name 1))))
                        (t (intern (upcase name)))))))
 		arglist)))