Add with block parameter support

Fixes #1042

lib/handlebars/base.js

@@ -194,13 +194,16 @@ function registerDefaultHelpers(instance) {
     let fn = options.fn;
 
     if (!Utils.isEmpty(context)) {
+      let data = options.data;
       if (options.data && options.ids) {
-        let data = createFrame(options.data);
+        data = createFrame(options.data);
         data.contextPath = Utils.appendContextPath(options.data.contextPath, options.ids[0]);
-        options = {data: data};
       }
 
-      return fn(context, options);
+      return fn(context, {
+        data: data,
+        blockParams: Utils.blockParams([context], [data.contextPath])
+      });
     } else {
       return options.inverse(this);
     }

spec/builtins.js

@@ -47,6 +47,10 @@ describe('builtin helpers', function() {
       var string = '{{#with person}}Person is present{{else}}Person is not present{{/with}}';
       shouldCompileTo(string, {}, 'Person is not present');
     });
+    it('with provides block parameter', function() {
+      var string = '{{#with person as |foo|}}{{foo.first}} {{last}}{{/with}}';
+      shouldCompileTo(string, {person: {first: 'Alan', last: 'Johnson'}}, 'Alan Johnson');
+    });
   });
 
   describe('#each', function() {