Fix a case where left side of assignment is not MemberExpression

This commit also move `isStateMemberExpression` from
`no-direct-mutation-state` rule into `util/Components` so that the logic
could be share with other rules.

Author: lukyth

lib/rules/no-direct-mutation-state.js

@@ -59,15 +59,6 @@ module.exports = {
       return node;
     }
 
-    /**
-     * Determine if this MemberExpression is for `this.state`
-     * @param {Object} node The node to process
-     * @returns {Boolean}
-     */
-    function isStateMemberExpression(node) {
-      return node.object.type === 'ThisExpression' && node.property.name === 'state';
-    }
-
     /**
      * Determine if we should currently ignore assignments in this component.
      * @param {?Object} component The component to process
@@ -101,7 +92,7 @@ module.exports = {
           return;
         }
         const item = getOuterMemberExpression(node.left);
-        if (isStateMemberExpression(item)) {
+        if (utils.isStateMemberExpression(item)) {
           const mutations = (component && component.mutations) || [];
           mutations.push(node.left.object);
           components.set(node, {
@@ -117,7 +108,7 @@ module.exports = {
           return;
         }
         const item = getOuterMemberExpression(node.argument);
-        if (isStateMemberExpression(item)) {
+        if (utils.isStateMemberExpression(item)) {
           const mutations = (component && component.mutations) || [];
           mutations.push(item);
           components.set(node, {

lib/rules/state-in-constructor.js

@@ -43,8 +43,7 @@ module.exports = {
       AssignmentExpression(node) {
         if (
           option === 'never' &&
-          node.left.object.type === 'ThisExpression' &&
-          node.left.property.name === 'state' &&
+          utils.isStateMemberExpression(node.left) &&
           utils.inConstructor() &&
           utils.getParentES6Component()
         ) {

lib/util/Components.js

@@ -321,6 +321,15 @@ function componentRule(rule, context) {
       return false;
     },
 
+    /**
+     * Determine if the node is MemberExpression of `this.state`
+     * @param {Object} node The node to process
+     * @returns {Boolean}
+     */
+    isStateMemberExpression: function(node) {
+      return node.type === 'MemberExpression' && node.object.type === 'ThisExpression' && node.property.name === 'state';
+    },
+
     getReturnPropertyAndNode(ASTnode) {
       let property;
       let node = ASTnode;

tests/lib/rules/state-in-constructor.js

@@ -198,6 +198,31 @@ ruleTester.run('state-in-constructor', rule, {
         }
       }
     `
+  }, {
+    code: `
+      class Foo extends React.Component {
+        constructor(props) {
+          super(props)
+          foobar = { bar: 0 }
+        }
+        render() {
+          return <div>Foo</div>
+        }
+      }
+    `
+  }, {
+    code: `
+      class Foo extends React.Component {
+        constructor(props) {
+          super(props)
+          foobar = { bar: 0 }
+        }
+        render() {
+          return <div>Foo</div>
+        }
+      }
+    `,
+    options: ['never']
   }],
 
   invalid: [{