Improve sanity checks in compiler and visitor

lib/handlebars/compiler/compiler.js

@@ -90,6 +90,11 @@ Compiler.prototype = {
   },
 
   accept: function(node) {
+    /* istanbul ignore next: Sanity code */
+    if (!this[node.type]) {
+      throw new Exception('Unknown type: ' + node.type, node);
+    }
+
     this.sourceNode.unshift(node);
     let ret = this[node.type](node);
     this.sourceNode.shift();

lib/handlebars/compiler/visitor.js

@@ -12,8 +12,9 @@ Visitor.prototype = {
   acceptKey: function(node, name) {
     let value = this.accept(node[name]);
     if (this.mutating) {
-      // Hacky sanity check:
-      if (value && typeof value.type !== 'string') {
+      // Hacky sanity check: This may have a few false positives for type for the helper
+      // methods but will generally do the right thing without a lot of overhead.
+      if (value && !Visitor.prototype[value.type]) {
         throw new Exception('Unexpected node type "' + value.type + '" found when accepting ' + name + ' on ' + node.type);
       }
       node[name] = value;
@@ -49,6 +50,11 @@ Visitor.prototype = {
       return;
     }
 
+    /* istanbul ignore next: Sanity code */
+    if (!this[object.type]) {
+      throw new Exception('Unknown type: ' + object.type, object);
+    }
+
     if (this.current) {
       this.parents.unshift(this.current);
     }