Trim trailing whitespace in Sprockets::SourceLine#to_s

lib/sprockets/source_line.rb

@@ -57,14 +57,26 @@ def inspect
     end
 
     def to_s(constants = source_file.environment.constants)
-      line.chomp.gsub(/<%=(.*?)%>/) do
-        constant = $1.strip
-        if value = constants[constant]
-          value
-        else
-          raise UndefinedConstantError, "couldn't find constant `#{constant}' in #{inspect}"
-        end
-      end + $/
+      result = line.chomp
+      interpolate_constants!(result, constants)
+      strip_trailing_whitespace!(result)
+      result + $/
     end
+
+    protected
+      def interpolate_constants!(result, constants)
+        result.gsub!(/<%=(.*?)%>/) do
+          constant = $1.strip
+          if value = constants[constant]
+            value
+          else
+            raise UndefinedConstantError, "couldn't find constant `#{constant}' in #{inspect}"
+          end
+        end
+      end
+
+      def strip_trailing_whitespace!(result)
+        result.gsub!(/\s+$/, "")
+      end
   end
 end

test/test_source_line.rb

@@ -82,4 +82,8 @@ def test_interpolation_of_missing_constant_raises_undefined_constant_error
       source_line('<%= NONEXISTENT %>').to_s("VERSION" => "1.0")
     end
   end
+
+  def test_to_s_should_strip_trailing_whitespace_before_adding_line_ending
+    assert_equal "hello();\n", source_line("hello();     \t  \r\n").to_s({})
+  end
 end