File mode specification error: (void-variable c-syntactic-context)

[Bruce Korb <bruce.korb@gmail.com>]

So I turned on debugging.  I got what looks like a trace, but it is
pretty indecipherable to me.
Can anyone make sense of this?  I am trying to use .dir-locals.el for
setting c style to linux:


(
 (nil . ((indent-tabs-mode . t)
(tab-width . 8)
         (show-trailing-whitespace . t)
(fill-column . 120)))

 (c-mode . ((c-file-style . "linux")))
)

The trace:


Debugger entered--Lisp error: (void-variable c-syntactic-context)
  (assq (quote cpp-macro) c-syntactic-context)
  (or (assq (quote cpp-macro) c-syntactic-context) (assq (quote
comment-intro) c-syntactic-context))
  (not (or (assq (quote cpp-macro) c-syntactic-context) (assq (quote
comment-intro) c-syntactic-context)))
  (and (not (or (assq (quote cpp-macro) c-syntactic-context) (assq
(quote comment-intro) c-syntactic-context))) (c-intersect-lists
c-inside-block-syms c-syntactic-context) (save-excursion
(back-to-indentation) (< (current-column)
c-label-minimum-indentation)))
  (if (and (not (or (assq (quote cpp-macro) c-syntactic-context) (assq
(quote comment-intro) c-syntactic-context))) (c-intersect-lists
c-inside-block-syms c-syntactic-context) (save-excursion
(back-to-indentation) (< (current-column)
c-label-minimum-indentation))) (progn (c-shift-line-indentation (-
c-label-minimum-indentation (current-indentation)))))
  c-gnu-impose-minimum()
  my-c-mode-common-hook()
  run-hooks(change-major-mode-after-body-hook c-mode-common-hook c-mode-hook)
  apply(run-hooks (change-major-mode-after-body-hook
c-mode-common-hook c-mode-hook))
  run-mode-hooks(c-mode-common-hook c-mode-hook)
  c-mode()
  set-auto-mode-0(c-mode nil)
  set-auto-mode()
  normal-mode(t)
  after-find-file(nil t)
  find-file-noselect-1(#<buffer event-xfer.c>
"~/workspace/skyhawk/evt/src/event-xfer.c" nil nil
"~/workspace/skyhawk/evt/src/event-xfer.c" (5388127 2304))
  find-file-noselect("~/workspace/skyhawk/evt/src/event-xfer.c" nil nil t)
  find-file("~/workspace/skyhawk/evt/src/event-xfer.c" t)
  call-interactively(find-file nil nil)


$ emacs --version
GNU Emacs 24.3.1
Copyright (C) 2013 Free Software Foundation, Inc.
[..]