fix bug: cache actually not working (#664)

Resolve issue #663 and add test.

mustache.js

@@ -444,10 +444,11 @@
    */
   Writer.prototype.parse = function parse (template, tags) {
     var cache = this.cache;
-    var tokens = cache[template];
+    var cacheKey = template + ':' + (tags || mustache.tags).join(':');
+    var tokens = cache[cacheKey];
 
     if (tokens == null)
-      tokens = cache[template + ':' + (tags || mustache.tags).join(':')] = parseTemplate(template, tags);
+      tokens = cache[cacheKey] = parseTemplate(template, tags);
 
     return tokens;
   };

test/parse-test.js

@@ -53,6 +53,10 @@ var expectations = {
                                             : [ [ '#', 'foo', 0, 8, [ [ '#', 'a', 11, 17, [ [ 'text', '    ', 18, 22 ], [ 'name', 'b', 22, 27 ], [ 'text', '\n', 27, 28 ] ], 30 ] ], 37 ] ]
 };
 
+beforeEach(function (){
+  Mustache.clearCache();
+});
+
 describe('Mustache.parse', function () {
 
   for (var template in expectations) {
@@ -135,4 +139,15 @@ describe('Mustache.parse', function () {
     });
   });
 
+  describe('when parsing a template with the same tags second time, return the cached tokens', function () {
+    it('returns the same tokens for the latter parse', function () {
+      var template = '{{foo}}[bar]';
+      var parsedResult1 = Mustache.parse(template);
+      var parsedResult2 = Mustache.parse(template);
+
+      assert.deepEqual(parsedResult1, parsedResult2);
+      assert.ok(parsedResult1 === parsedResult2);
+    });
+  });
+
 });