* lisp/progmodes/prog-mode.el (prettify-symbols--compose-symbol): Refine.

Fix handling of symbols with different syntax at beginning/end or with
symbol rather than word syntax.

lisp/ChangeLog

+2014-12-01  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* progmodes/prog-mode.el (prettify-symbols--compose-symbol):
+	Fix handling of symbols with different syntax at beginning/end or with
+	symbol rather than word syntax.
+
 2014-11-30  Eli Zaretskii  <eliz@gnu.org>
 	* simple.el (line-move): If noninteractive, call line-move-1, not

lisp/progmodes/prog-mode.el

@@ -66,11 +66,13 @@ Regexp match data 0 points to the chars."
   ;; Check that the chars should really be composed into a symbol.
   (let* ((start (match-beginning 0))
 	 (end (match-end 0))
-	 (syntaxes (if (eq (char-syntax (char-after start)) ?w)
+	 (syntaxes-beg (if (memq (char-syntax (char-after start)) '(?w ?_))
+                           '(?w ?_) '(?. ?\\)))
+	 (syntaxes-end (if (memq (char-syntax (char-before end)) '(?w ?_))
 		       '(?w ?_) '(?. ?\\)))
 	 match)
-    (if (or (memq (char-syntax (or (char-before start) ?\s)) syntaxes)
-	    (memq (char-syntax (or (char-after end) ?\s)) syntaxes)
+    (if (or (memq (char-syntax (or (char-before start) ?\s)) syntaxes-beg)
+	    (memq (char-syntax (or (char-after end) ?\s)) syntaxes-end)
             ;; syntax-ppss could modify the match data (bug#14595)
             (progn (setq match (match-string 0)) (nth 8 (syntax-ppss))))
 	;; No composition for you.  Let's actually remove any composition