Prevent context overwrite by replaceStack

Fixes #408.

lib/handlebars/compiler/compiler.js

@@ -886,21 +886,28 @@ Handlebars.JavaScriptCompiler = function() {};
     },
 
     pushStack: function(item) {
-      this.source.push(this.incrStack() + " = " + item + ";");
-      this.compileStack.push("stack" + this.stackSlot);
-      return "stack" + this.stackSlot;
+      var stack = this.incrStack();
+      this.source.push(stack + " = " + item + ";");
+      this.compileStack.push(stack);
+      return stack;
     },
 
     replaceStack: function(callback) {
-      var item = callback.call(this, this.topStack());
+      var stack = this.topStack(),
+          item = callback.call(this, stack);
 
-      this.source.push(this.topStack() + " = " + item + ";");
-      return "stack" + this.stackSlot;
+      // Prevent modification of the context depth variable. Through replaceStack
+      if (this.compileStack.length <= 1) {
+        stack = this.nextStack();
+      }
+
+      this.source.push(stack + " = " + item + ";");
+      return stack;
     },
 
     nextStack: function(skipCompileStack) {
       var name = this.incrStack();
-      this.compileStack.push("stack" + this.stackSlot);
+      this.compileStack.push(name);
       return name;
     },
 

spec/qunit_spec.js

@@ -1282,3 +1282,15 @@ test("Passing falsy values to Handlebars.compile throws an error", function() {
     CompilerContext.compile(null);
   }, "You must pass a string to Handlebars.compile. You passed null");
 });
+
+test('GH-408: Multiple loops fail', function() {
+  var context = [
+    { name: "John Doe", location: { city: "Chicago" } },
+    { name: "Jane Doe", location: { city: "New York"} }
+  ];
+
+  var template = CompilerContext.compile('{{#.}}{{name}}{{/.}}{{#.}}{{name}}{{/.}}');
+
+  var result = template(context);
+  equals(result, "John DoeJane DoeJohn DoeJane Doe", 'It should output twice');
+});