fix(runtime.js): partials compile not caching

lib/handlebars/runtime.js

@@ -124,6 +124,15 @@ export function template(templateSpec, env) {
       }
       return value;
     },
+    mergeIfNeeded: function(param, common) {
+      let obj = param || common;
+
+      if (param && common && (param !== common)) {
+        obj = Utils.extend({}, common, param);
+      }
+
+      return obj;
+    },
     // An empty object to use as replacement for null-contexts
     nullContext: Object.seal({}),
 
@@ -161,7 +170,8 @@ export function template(templateSpec, env) {
       container.helpers = Utils.extend({}, env.helpers, options.helpers);
 
       if (templateSpec.usePartial) {
-        container.partials = Utils.extend({}, env.partials, options.partials);
+        // Use mergeIfNeeded here to prevent compiling global partials multiple times
+        container.partials = container.mergeIfNeeded(options.partials, env.partials);
       }
       if (templateSpec.usePartial || templateSpec.useDecorators) {
         container.decorators = Utils.extend({}, env.decorators, options.decorators);

spec/compiler.js

@@ -108,4 +108,29 @@ describe('compiler', function() {
       equal(/return ""/.test(Handlebars.precompile('')), true);
     });
   });
+
+  describe('Compile Partials Correctly', function() {
+    var compileCount = 0;
+    var origTemplateFunc = Handlebars.template;
+    before(function() {
+      Handlebars.template = function(params) {
+        compileCount++;
+        return origTemplateFunc(params);
+      };
+      Handlebars.registerPartial({
+        'dude': 'I am a partial'
+      });
+    });
+    after(function() {
+      Handlebars.template = origTemplateFunc;
+      Handlebars.unregisterPartial('dude');
+    });
+
+    it('should only compile global partials once', function() {
+      var string = 'Dudes: {{> dude}} {{> dude}}';
+      Handlebars.compile(string)(); // This should compile template + partial once
+      Handlebars.compile(string)(); // This should only compile template
+      equal(compileCount, 3);
+    });
+  });
 });