Correctly recognize ? character quote tokens

This introduces a syntax-propertize function that will ferret out
non-constituent ? characters and apply the generic string delimiter
syntax text property to it and the character it escapes. (This handles
?\# sequences too.)

Fixes #26.

Author: Michael Swan

elixir-mode.el

@@ -342,9 +342,6 @@
 
 (defconst elixir-mode-font-lock-defaults
   (list
-   ;; comments:
-   '("#.*$" . font-lock-comment-face)
-
    ;; records and modules at point of definition:
    '("^\\s *def\\(module\\|record\\|protocol\\|impl\\)\\s +\\([^( \t\n,]+\\)" 2 font-lock-type-face)
 
@@ -551,6 +548,8 @@ Argument END End of the region."
   (set (make-local-variable 'comment-end) "")
   (set (make-variable-buffer-local 'tab-width) elixir-basic-offset)
   (set (make-variable-buffer-local 'default-tab-width) elixir-basic-offset)
+  (if (boundp 'syntax-propertize-function)
+      (set (make-local-variable 'syntax-propertize-function) 'elixir-syntax-propertize))
   (smie-setup elixir-smie-grammar 'verbose-elixir-smie-rules ; 'elixir-smie-rules
               :forward-token 'elixir-smie-forward-token
               :backward-token 'elixir-smie-backward-token)

elixir-smie.el

@@ -12,7 +12,12 @@
 
 (defvar elixir-mode-syntax-table
   (let ((elixir-mode-syntax-table (make-syntax-table)))
+
+    ;; Note that ?_ might be better as class "_", but either seems to
+    ;; work:
     (modify-syntax-entry ?_ "w" elixir-mode-syntax-table)
+    (modify-syntax-entry ?? "w" elixir-mode-syntax-table)
+
     (modify-syntax-entry ?' "\"" elixir-mode-syntax-table)
     (modify-syntax-entry ?# "<" elixir-mode-syntax-table)
     (modify-syntax-entry ?\n ">" elixir-mode-syntax-table)
@@ -27,6 +32,30 @@
     elixir-mode-syntax-table)
   "Elixir mode syntax table.")
 
+(defun elixir-syntax-propertize (start end)
+  (save-excursion
+    (goto-char start)
+    ;; The ? character on its own is supposed to escape whatever comes
+    ;; after it (including any escaped chars. Examples: ?\# and ?#.
+    (while (search-forward "?" end t)
+      (unless (or (= (char-syntax (char-before (- (point) 1))) ?w)
+                  (= (char-syntax (char-before (- (point) 1))) ?_))
+        (put-text-property (1- (point))
+                           (point)
+                           'syntax-table
+                           '(?|))
+        (when (= (char-after) ?\\)
+          (forward-char)
+          (put-text-property (1- (point))
+                             (point)
+                             'syntax-table
+                             '(?\s)))
+        (forward-char)
+        (put-text-property (1- (point))
+                           (point)
+                           'syntax-table
+                           '(?|))))))
+
 (defmacro elixir-smie-debug (message &rest format-args)
   `(progn
      (when elixir-smie-verbose-p
@@ -79,7 +108,7 @@ Return non-nil if any line breaks were skipped."
 
 Return non-nil if any line breaks were skipped."
   (let ((start-line-no (line-number-at-pos (point))))
-    (forward-comment (point))
+    (forward-comment (buffer-size))
     (/= start-line-no (line-number-at-pos (point)))))
 
 (defun elixir-smie-next-token-no-lookaround (forwardp nested)