Provide better error on unexpected template

Fixes #806

lib/handlebars/runtime.js

@@ -27,6 +27,9 @@ export function template(templateSpec, env) {
   if (!env) {
     throw new Exception("No environment passed to template");
   }
+  if (!templateSpec || !templateSpec.main) {
+    throw new Exception('Unknown template object: ' + typeof templateSpec);
+  }
 
   // Note: Using env.VM references rather than local var references throughout this section to allow
   // for external users to override these as psuedo-supported APIs.
@@ -151,6 +154,7 @@ export function template(templateSpec, env) {
       throw new Exception('_child can not be used with depthed methods');
     }
 
+    // TODO : Fix this
     return container.programWithDepth(i);
   };
   return ret;

spec/runtime.js

@@ -0,0 +1,36 @@
+/*globals Handlebars, shouldThrow */
+
+describe('runtime', function() {
+  describe('#template', function() {
+    it('should throw on invalid templates', function() {
+      shouldThrow(function() {
+        Handlebars.template({});
+      }, Error, 'Unknown template object: object');
+      shouldThrow(function() {
+        Handlebars.template();
+      }, Error, 'Unknown template object: undefined');
+      shouldThrow(function() {
+        Handlebars.template('');
+      }, Error, 'Unknown template object: string');
+    });
+    it('should throw on version mismatch', function() {
+      shouldThrow(function() {
+        Handlebars.template({
+          main: true,
+          compiler: [Handlebars.COMPILER_REVISION + 1]
+        });
+      }, Error, /Template was precompiled with a newer version of Handlebars than the current runtime/);
+      shouldThrow(function() {
+        Handlebars.template({
+          main: true,
+          compiler: [Handlebars.COMPILER_REVISION - 1]
+        });
+      }, Error, /Template was precompiled with an older version of Handlebars than the current runtime/);
+      shouldThrow(function() {
+        Handlebars.template({
+          main: true
+        });
+      }, Error, /Template was precompiled with an older version of Handlebars than the current runtime/);
+    });
+  });
+});