* files.el (hack-local-variables): Warn about misplaced lexical-binding.

(hack-local-variables--warned-lexical): New.

Fixes: debbugs:15616

2 files changed, 19 insertions, 7 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 50ef17cfef1..476c0593855 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,9 @@
 2013-10-16  Glenn Morris  <rgm@gnu.org>
 
+        * files.el (hack-local-variables--warned-lexical): New.
+        (hack-local-variables):
+        Warn about misplaced lexical-binding.  (Bug#15616)
+
         * net/eww.el (eww-render): Always set eww-current-url,
         and update header line.  (Bug#15622)
         (eww-display-html): ... Rather than just doing it here.
diff --git a/lisp/files.el b/lisp/files.el
index ab62be295f0..cf3356014a1 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3154,6 +3154,9 @@ DIR-NAME is the name of the associated directory.  Otherwise it is nil."
                    (assq-delete-all (car elt) file-local-variables-alist)))
            (push elt file-local-variables-alist)))))
 
+;; TODO?  Warn once per file rather than once per session?
+(defvar hack-local-variables--warned-lexical nil)
+
 (defun hack-local-variables (&optional mode-only)
   "Parse and put into effect this buffer's local variables spec.
 Uses `hack-local-variables-apply' to apply the variables.
@@ -3275,13 +3278,18 @@ local variables, but directory-local variables may still be applied."
                                      "-minor\\'"
                                      (setq val2 (downcase (symbol-name val)))))
                                (setq result (intern (concat val2 "-mode"))))
-                        (unless (eq var 'coding)
-                          (condition-case nil
-                              (push (cons (if (eq var 'eval)
-                                              'eval
-                                            (indirect-variable var))
-                                          val) result)
-                            (error nil)))))
+                        (cond ((eq var 'coding))
+                              ((eq var 'lexical-binding)
+                               (unless hack-local-variables--warned-lexical
+                                 (setq hack-local-variables--warned-lexical t)
+                                 (display-warning :warning
+                                                  "Specify `lexical-binding' on the first line, not at the end")))
+                              (t
+                               (ignore-errors
+                                 (push (cons (if (eq var 'eval)
+                                                 'eval
+                                               (indirect-variable var))
+                                             val) result))))))
                     (forward-line 1))))))))
       ;; Now we've read all the local variables.
       ;; If MODE-ONLY is non-nil, return whether the mode was specified.