Implement inline partials

Allows for partials to be defined within the current template to allow for localized code reuse as well as for conditional behavior within nested partials.

Fixes #1018

lib/handlebars/decorators.js

@@ -1,5 +1,6 @@
 import registerInline from './decorators/inline';
 
 export function registerDefaultDecorators(instance) {
+  registerInline(instance);
 }
 

lib/handlebars/decorators/inline.js

@@ -0,0 +1,22 @@
+import {extend} from '../utils';
+
+export default function(instance) {
+  instance.registerDecorator('inline', function(fn, props, container, options) {
+    let ret = fn;
+    if (!props.partials) {
+      props.partials = {};
+      ret = function(context, options) {
+        // Create a new partials stack frame prior to exec.
+        let original = container.partials;
+        container.partials = extend({}, original, props.partials);
+        let ret = fn(context, options);
+        container.partials = original;
+        return ret;
+      };
+    }
+
+    props.partials[options.args[0]] = options.fn;
+
+    return ret;
+  });
+}

lib/handlebars/runtime.js

@@ -239,6 +239,10 @@ export function invokePartial(partial, context, options) {
   let partialBlock;
   if (options.fn && options.fn !== noop) {
     partialBlock = options.data['partial-block'] = options.fn;
+
+    if (partialBlock.partials) {
+      options.partials = Utils.extend({}, options.partials, partialBlock.partials);
+    }
   }
 
   if (partial === undefined && partialBlock) {