Parse string interpolation in attribute value

Fix #917

lib/haml/attribute_parser.rb

@@ -131,6 +131,10 @@ def each_balaned_tokens(tokens, &block)
             open_tokens[:paren] += 1
           when :on_rparen
             open_tokens[:paren] -= 1
+          when :on_embexpr_beg
+            open_tokens[:embexpr] += 1
+          when :on_embexpr_end
+            open_tokens[:embexpr] -= 1
           when *IGNORED_TYPES
             next if attr_tokens.empty?
           end

test/attribute_parser_test.rb

@@ -65,6 +65,10 @@ def assert_parse(expected, haml)
         it { assert_parse(nil, '%Q[f#{o}o] => bar ') }
       end
 
+      describe 'string interpolation' do
+        it { assert_parse({ 'foo' => %q["#{bar baz, '/abc/'}"] }, %q[{foo: "#{bar baz, '/abc/'}"}]) }
+      end
+
       describe 'multi lines' do
         it { assert_parse({ 'a' => 'b', 'c' => 'd' }, "{a: b,\nc: d}") }
       end

test/engine_test.rb

@@ -151,6 +151,13 @@ def test_ruby_code_should_work_inside_attributes
     assert_equal("<p class='3'>foo</p>", render("%p{:class => 1+2} foo").chomp)
   end
 
+  def test_attributes_with_interpolation
+    assert_equal("<iframe id='test' src='http://www.google.com/abc/'></iframe>\n", render(<<-'HAML'))
+- base_url = "http://www.google.com"
+%iframe#test{src: "#{File.join base_url, '/abc/'}"}
+    HAML
+  end
+
   def test_class_attr_with_array
     assert_equal("<p class='a b'>foo</p>\n", render("%p{:class => %w[a b]} foo")) # basic
     assert_equal("<p class='a b css'>foo</p>\n", render("%p.css{:class => %w[a b]} foo")) # merge with css