bug#22955: 25.1.50; *Help* xref for generic methods broken

[Eric Abrahamsen]

If you `describe-function' on a generic method, the resulting *Help*
buffer shows the various implementations correctly. However,
clicking/RET on the implementation links fails with:

Debugger entered--Lisp error: (wrong-number-of-arguments (lambda (fun file) 
(require (quote find-func)) (if (eq file (quote C-source)) (progn (setq file 
(help-C-file-name (indirect-function fun) (quote fun))))) (let ((location 
(find-function-search-for-symbol fun nil file))) 
(my-find-symbol-switch-to-buffer (car location)) (if (cdr location) (goto-char 
(cdr location)) (message "Unable to find location in file")))) 3)
  help-do-xref(nil (lambda (fun file) (require (quote find-func)) (if (eq file 
(quote C-source)) (progn (setq file (help-C-file-name (indirect-function fun) 
(quote fun))))) (let ((location (find-function-search-for-symbol fun nil 
file))) (my-find-symbol-switch-to-buffer (car location)) (if (cdr location) 
(goto-char (cdr location)) (message "Unable to find location in file")))) 
((bbdb-db-load bbdb-db) "/home/eric/.emacs.d/bbdb/lisp/bbdb.el" cl-defmethod))
  help-button-action(#<marker (moves after insertion) at 276 in *Help*>)
  button-activate(#<marker (moves after insertion) at 276 in *Help*> nil)
  push-button(276)
  funcall-interactively(push-button 276)
  call-interactively(push-button nil nil)
  command-execute(push-button)

Basically, when `help-button-action' does this:

(help-do-xref nil
                (button-get button 'help-function)
                (button-get button 'help-args))

There are three 'help-args (the first arg is the specializer --
actually, maybe there as many args as there are specializers? don't
know), but the 'help-function only takes two args.

Hope that's enough to get it there!

In GNU Emacs 25.1.50.17 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.8)
 of 2016-03-08 built on clem
Repository revision: 59c7a5d71145d88933a535e222bdf30105e7d382
Windowing system distributor 'The X.Org Foundation', version 11.0.11801000
Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_CTYPE: zh_CN.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
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  global-company-mode: t
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  show-paren-mode: t
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  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
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  file-name-shadow-mode: t
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  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t