describe-variable error when using dir-locals-set-directory-class

[Hongxu Chen]

Hi,

  I followed the docs on this page
  
http://www.gnu.org/software/emacs/manual/html_node/emacs/Directory-Variables.html
  and does some tweaks for the directory variables for ffap-c-path.

#+BEGIN_SRC emacs-lisp
(dir-locals-set-class-variables 'llvm-3.4-directory
                                '((nil . ((ffap-c-path . 
("/usr/lib/llvm-3.4/include"))))))
(dir-locals-set-directory-class
 "/usr/lib/llvm-3.4/include/clang-c/" 'llvm-3.4-directory)
#+END_SRC

  However when I try `C-h v ffap-c-path', there is an error;
  when I `toggle-debug-on-error', it reports:

#+BEGIN_SRC emacs-lisp
  Debugger entered--Lisp error: (wrong-type-argument char-or-string-p 
("/usr/lib/llvm-3.4/include/clang-c/" llvm-3\.4-directory nil))
  insert-text-button(("/usr/lib/llvm-3.4/include/clang-c/" llvm-3\.4-directory 
nil) type help-dir-local-var-def help-args (ac-clang-flags 
("/usr/lib/llvm-3.4/include/clang-c/" llvm-3\.4-directory nil)))
  describe-variable(ac-clang-flags)
  call-interactively(describe-variable nil nil)
#+END_SRC

  And describe-variable ONLY sucks for those variables that are set
  using this sort of syntax.
  
  Also, I am wondering whether this kind of directory variable setting
  can accept `evil' syntax just as `.dir-locals.el' does.


-- 
Regards,
Hongxu Chen