Start doing earlier work on helpers

lib/handlebars/compiler/ast.js

@@ -11,12 +11,26 @@ var Handlebars = require('./base');
     if(inverse) { this.inverse = new Handlebars.AST.ProgramNode(inverse); }
   };
 
-  Handlebars.AST.MustacheNode = function(params, hash, unescaped) {
+  Handlebars.AST.MustacheNode = function(rawParams, hash, unescaped) {
     this.type = "mustache";
-    this.id = params[0];
-    this.params = params.slice(1);
-    this.hash = hash;
     this.escaped = !unescaped;
+    this.hash = hash;
+
+    var id = this.id = rawParams[0];
+    var params = this.params = rawParams.slice(1);
+
+    // a mustache is an eligible helper if:
+    // * its id is simple (a single part, not `this` or `..`)
+    var eligibleHelper = this.eligibleHelper = id.isSimple;
+
+    // a mustache is definitely a helper if:
+    // * it is an eligible helper, and
+    // * it has at least one parameter or hash segment
+    this.isHelper = eligibleHelper && (params.length || hash);
+
+    // if a mustache is an eligible helper but not a definite
+    // helper, it is ambiguous, and will be resolved in a later
+    // pass or at runtime.
   };
 
   Handlebars.AST.PartialNode = function(id, context) {
@@ -75,7 +89,10 @@ var Handlebars = require('./base');
     this.parts    = dig;
     this.string   = dig.join('.');
     this.depth    = depth;
-    this.isSimple = (dig.length === 1) && (depth === 0);
+
+    // an ID is simple if it only has one part, and that part is not
+    // `..` or `this`.
+    this.isSimple = parts.length === 1 && !this.isScoped && depth === 0;
   };
 
   Handlebars.AST.StringNode = function(string) {