* lisp/progmodes/ruby-mode.el (ruby-syntax-expansion-allowed-p):

Highlight expansions inside regexp literals.

lisp/ChangeLog

@@ -1,3 +1,8 @@
+2013-05-31  Dmitry Gutov  <dgutov@yandex.ru>
+
+	* progmodes/ruby-mode.el (ruby-syntax-expansion-allowed-p):
+	Highlight expansions inside regexp literals.
+
 2013-05-31  Glenn Morris  <rgm@gnu.org>
 
 	* obsolete/sym-comp.el (symbol-complete):

lisp/progmodes/ruby-mode.el

@@ -1513,7 +1513,7 @@ It will be properly highlighted even when the call omits parens.")
         "Return non-nil if expression expansion is allowed."
         (let ((term (nth 3 parse-state)))
           (cond
-           ((memq term '(?\" ?` ?\n)))
+           ((memq term '(?\" ?` ?\n ?/)))
            ((eq term t)
             (save-match-data
               (save-excursion

test/automated/ruby-mode-tests.el

@@ -112,6 +112,9 @@ VALUES-PLIST is a list with alternating index and value elements."
 (ert-deftest ruby-regexp-starts-after-string ()
   (ruby-assert-state "'(/', /\d+/" 3 ?/ 8))
 
+(ert-deftest ruby-regexp-interpolation-is-highlighted ()
+  (ruby-assert-face "/#{foobs}/" 4 font-lock-variable-name-face))
+
 (ert-deftest ruby-regexp-skips-over-interpolation ()
   (ruby-assert-state "/#{foobs.join('/')}/" 3 nil))