Protect context-lookups from undefined values

Fixes #166
Fixes #587

lib/handlebars/compiler/javascript-compiler.js

@@ -10,13 +10,25 @@ JavaScriptCompiler.prototype = {
   // PUBLIC API: You can override these methods in a subclass to provide
   // alternative compiled forms for name lookup and buffering semantics
   nameLookup: function(parent, name /* , type*/) {
+    var wrap,
+        ret;
+    if (parent.indexOf('depth') === 0) {
+      wrap = true;
+    }
+
     if (/^[0-9]+$/.test(name)) {
-      return parent + "[" + name + "]";
+      ret = parent + "[" + name + "]";
     } else if (JavaScriptCompiler.isValidJavaScriptVariableName(name)) {
-      return parent + "." + name;
+      ret = parent + "." + name;
     }
     else {
-      return parent + "['" + name + "']";
+      ret = parent + "['" + name + "']";
+    }
+
+    if (wrap) {
+      return '(' + parent + ' && ' + ret + ')';
+    } else {
+      return ret;
     }
   },
 

spec/basic.js

@@ -22,6 +22,12 @@ describe("basic context", function() {
                     "It works if all the required keys are provided");
   });
 
+  it("compiling with an undefined context", function() {
+    shouldCompileTo("Goodbye\n{{cruel}}\n{{world.bar}}!", undefined, "Goodbye\n\n!");
+
+    shouldCompileTo("{{#unless foo}}Goodbye{{../test}}{{test2}}{{/unless}}", undefined, "Goodbye");
+  });
+
   it("comments", function() {
     shouldCompileTo("{{! Goodbye}}Goodbye\n{{cruel}}\n{{world}}!",
       {cruel: "cruel", world: "world"}, "Goodbye\ncruel\nworld!",

spec/partials.js

@@ -16,6 +16,13 @@ describe('partials', function() {
                     "Partials can be passed a context");
   });
 
+  it("partials with undefined context", function() {
+    var string = "Dudes: {{>dude dudes}}";
+    var partial = "{{foo}} Empty";
+    var hash = {};
+    shouldCompileToWithPartials(string, [hash, {}, {dude: partial}], true, "Dudes:  Empty");
+  });
+
   it("partial in a partial", function() {
     var string = "Dudes: {{#dudes}}{{>dude}}{{/dudes}}";
     var dude = "{{name}} {{> url}} ";