Add rule no-class-prototype-attributes

[closes #2]

README.md

@@ -58,3 +58,11 @@ Then configure the rules you want to use under the rules section.
     }.property('firstName', 'lastName')
   })
   ```
+
+* `no-class-prototype-attributes` - For certain Ember objects, some properties
+  must be set on the prototype when extending a factory (`classNames`,
+  `actions`). However when setting default properties for an object, in most
+  cases one should use the `init` hook. This is especially important when
+  setting values to objects or arrays that will be shared (likely inadvertently)
+  across instances.  This rule warns when properties are set on the prototype
+  that should instead be initialized inside of the `init` hook.

lib/rules/no-class-prototype-attributes.js

@@ -0,0 +1,45 @@
+"use strict";
+
+var prohibitedPrototypeSyntax = {
+  'ArrayExpression': true,
+  'ObjectExpression': true,
+  'Literal': true
+}
+
+var whitelistedProperties = {
+  'actions': true,
+  'attributeBindings': true,
+  'classNameBindings': true,
+  'classNames': true,
+  'concatenatedProperties': true,
+  'mergedProperties': true,
+  'queryParams': true
+}
+
+module.exports = function(context) {
+  function isInsideObjectExtension(node) {
+    return (
+      node.parent.type === 'ObjectExpression' &&
+      node.parent.parent.type === 'CallExpression' &&
+      node.parent.parent.callee.type === 'MemberExpression' &&
+      node.parent.parent.callee.property.name === 'extend'
+    );
+  }
+
+  function isWhitelistedProperty(node) {
+    return whitelistedProperties.hasOwnProperty(node.key.name);
+  }
+
+  return {
+    'Property': function(node) {
+      if (isInsideObjectExtension(node) && !isWhitelistedProperty(node)) {
+        if (prohibitedPrototypeSyntax.hasOwnProperty(node.value.type)) {
+          context.report({
+            node: node,
+            message: 'error'
+          });
+        }
+      }
+    }
+  };
+};

tests/lib/rules/no-class-prototype-attributes.js

@@ -0,0 +1,43 @@
+"use strict";
+
+var rule = require("../../../lib/rules/no-class-prototype-attributes");
+var RuleTester = require("eslint").RuleTester;
+
+var ruleTester = new RuleTester();
+
+ruleTester.run("no-class-prototype-attributes", rule, {
+  valid: [
+    "Class.extend({});",
+    "{ a: [] };",
+    "var b = { a: [] };",
+    "{ a: {} };",
+    "var a = {};",
+    "Class.extend({ a: computed() })",
+    "Class.extend({ a: identifier })",
+    "Class.extend({ a: identifier })",
+    "Class.extend({ actions: [] })",
+    "Class.extend({ attributeBindings: [] })",
+    "Class.extend({ classNameBindings: [] })",
+    "Class.extend({ classNames: [] })",
+    "Class.extend({ concatenatedProperties: [] })",
+    "Class.extend({ mergedProperties: [] })",
+    "Class.extend({ queryParams: [] })"
+  ],
+
+  invalid: [{
+    code: "Class.extend({ a: [] })",
+    errors: ["error"]
+  }, {
+    code: "Class.extend({ a: {} })",
+    errors: ["error"]
+  }, {
+    code: "Class.extend({ a: 1 })",
+    errors: ["error"]
+  }, {
+    code: "Class.extend({ a: true })",
+    errors: ["error"]
+  }, {
+    code: "Class.extend({ a: null })",
+    errors: ["error"]
+  }]
+});