Implement partial blocks

This allows for failover for missing partials as well as limited templating ability through the `{{> @partial-block }}` partial special case.

Partial fix for #1018

lib/handlebars/compiler/compiler.js

@@ -1,3 +1,5 @@
+/* eslint-disable new-cap */
+
 import Exception from '../exception';
 import {isArray, indexOf} from '../utils';
 import AST from './ast';
@@ -157,6 +159,11 @@ Compiler.prototype = {
   PartialStatement: function(partial) {
     this.usePartial = true;
 
+    let program = partial.program;
+    if (program) {
+      program = this.compileProgram(partial.program);
+    }
+
     let params = partial.params;
     if (params.length > 1) {
       throw new Exception('Unsupported number of partial arguments: ' + params.length, partial);
@@ -170,7 +177,7 @@ Compiler.prototype = {
       this.accept(partial.name);
     }
 
-    this.setupFullMustacheParams(partial, undefined, undefined, true);
+    this.setupFullMustacheParams(partial, program, undefined, true);
 
     let indent = partial.indent || '';
     if (this.options.preventIndent && indent) {
@@ -181,9 +188,12 @@ Compiler.prototype = {
     this.opcode('invokePartial', isDynamic, partialName, indent);
     this.opcode('append');
   },
+  PartialBlockStatement: function(partialBlock) {
+    this.PartialStatement(partialBlock);
+  },
 
   MustacheStatement: function(mustache) {
-    this.SubExpression(mustache);   // eslint-disable-line new-cap
+    this.SubExpression(mustache);
 
     if (mustache.escaped && !this.options.noEscape) {
       this.opcode('appendEscaped');