Implement block decorators

These allow for a given block to be wrapped in helper methods or metadata and allow for more control over the current container and method before the code is run.

lib/handlebars/compiler/javascript-compiler.js

@@ -64,6 +64,7 @@ JavaScriptCompiler.prototype = {
     this.name = this.environment.name;
     this.isChild = !!context;
     this.context = context || {
+      decorators: [],
       programs: [],
       environments: []
     };
@@ -81,7 +82,7 @@ JavaScriptCompiler.prototype = {
 
     this.compileChildren(environment, options);
 
-    this.useDepths = this.useDepths || environment.useDepths || this.options.compat;
+    this.useDepths = this.useDepths || environment.useDepths || environment.useDecorators || this.options.compat;
     this.useBlockParams = this.useBlockParams || environment.useBlockParams;
 
     let opcodes = environment.opcodes,
@@ -107,16 +108,43 @@ JavaScriptCompiler.prototype = {
       throw new Exception('Compile completed with content left on stack');
     }
 
+    if (!this.decorators.isEmpty()) {
+      this.useDecorators = true;
+
+      this.decorators.prepend('var decorators = container.decorators;\n');
+      this.decorators.push('return fn;');
+
+      if (asObject) {
+        this.decorators = Function.apply(this, ['fn', 'props', 'container', 'depth0', 'data', 'blockParams', 'depths', this.decorators.merge()]);
+      } else {
+        this.decorators.prepend('function(fn, props, container, depth0, data, blockParams, depths) {\n');
+        this.decorators.push('}\n');
+        this.decorators = this.decorators.merge();
+      }
+    } else {
+      this.decorators = undefined;
+    }
+
     let fn = this.createFunctionContext(asObject);
     if (!this.isChild) {
       let ret = {
         compiler: this.compilerInfo(),
         main: fn
       };
-      let programs = this.context.programs;
+
+      if (this.decorators) {
+        ret.main_d = this.decorators;   // eslint-disable-line camelcase
+        ret.useDecorators = true;
+      }
+
+      let {programs, decorators} = this.context;
       for (i = 0, l = programs.length; i < l; i++) {
         if (programs[i]) {
           ret[i] = programs[i];
+          if (decorators[i]) {
+            ret[i + '_d'] = decorators[i];
+            ret.useDecorators = true;
+          }
         }
       }
 
@@ -163,6 +191,7 @@ JavaScriptCompiler.prototype = {
     // getContext opcode when it would be a noop
     this.lastContext = 0;
     this.source = new CodeGen(this.options.srcName);
+    this.decorators = new CodeGen(this.options.srcName);
   },
 
   createFunctionContext: function(asObject) {
@@ -561,6 +590,24 @@ JavaScriptCompiler.prototype = {
     }
   },
 
+  // [registerDecorator]
+  //
+  // On stack, before: hash, program, params..., ...
+  // On stack, after: ...
+  //
+  // Pops off the decorator's parameters, invokes the decorator,
+  // and inserts the decorator into the decorators list.
+  registerDecorator(paramSize, name) {
+    let foundDecorator = this.nameLookup('decorators', name, 'decorator'),
+        options = this.setupHelperArgs(name, paramSize);
+
+    this.decorators.push([
+      'fn = ',
+      this.decorators.functionCall(foundDecorator, '', ['fn', 'props', 'container', options]),
+      ' || fn;'
+    ]);
+  },
+
   // [invokeHelper]
   //
   // On stack, before: hash, inverse, program, params..., ...
@@ -738,6 +785,7 @@ JavaScriptCompiler.prototype = {
         child.index = index;
         child.name = 'program' + index;
         this.context.programs[index] = compiler.compile(child, options, this.context, !this.precompile);
+        this.context.decorators[index] = compiler.decorators;
         this.context.environments[index] = child;
 
         this.useDepths = this.useDepths || compiler.useDepths;
@@ -946,7 +994,16 @@ JavaScriptCompiler.prototype = {
   },
 
   setupParams: function(helper, paramSize, params) {
-    let options = {}, contexts = [], types = [], ids = [], param;
+    let options = {},
+        contexts = [],
+        types = [],
+        ids = [],
+        objectArgs = !params,
+        param;
+
+    if (objectArgs) {
+      params = [];
+    }
 
     options.name = this.quotedString(helper);
     options.hash = this.popStack();
@@ -985,6 +1042,10 @@ JavaScriptCompiler.prototype = {
       }
     }
 
+    if (objectArgs) {
+      options.args = this.source.generateArray(params);
+    }
+
     if (this.trackIds) {
       options.ids = this.source.generateArray(ids);
     }
@@ -1009,9 +1070,11 @@ JavaScriptCompiler.prototype = {
       this.useRegister('options');
       params.push('options');
       return ['options=', options];
-    } else {
+    } else if (params) {
       params.push(options);
       return '';
+    } else {
+      return options;
     }
   }
 };