Allow this.state assignment on constructor

see #832

docs/rules/no-direct-mutation-state.md

@@ -1,8 +1,10 @@
 # Prevent direct mutation of this.state (react/no-direct-mutation-state)
 
-NEVER mutate `this.state` directly, as calling `setState()` afterwards may replace
+Don't mutate `this.state` directly, as calling `setState()` afterwards may replace
 the mutation you made. Treat `this.state` as if it were immutable.
 
+The only place that it's acceptable to assign this.state is on a ES6 class component constructor
+
 ## Rule Details
 
 This rule is aimed to forbid the use of mutating `this.state` directly.
@@ -34,4 +36,14 @@ var Hello = createReactClass({
     return <div>Hello {this.state.name}</div>;
   }
 });
+
+class Hello extends React.Component {
+  constructor(props) {
+    super(props)
+
+    this.state = {
+      foo: 'bar',
+    }
+  }
+}
 ```

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

@@ -1,10 +1,10 @@
 /**
  * @fileoverview Prevent direct mutation of this.state
  * @author David Petersen
+ * @author Nicolas Fernandez <@burabure>
  */
 'use strict';
 
-var has = require('has');
 var Components = require('../util/Components');
 
 // ------------------------------------------------------------------------------
@@ -49,11 +49,18 @@ module.exports = {
     // --------------------------------------------------------------------------
     // Public
     // --------------------------------------------------------------------------
+    var inConstructor = false;
 
     return {
-      AssignmentExpression: function(node) {
-        var item;
-        if (!node.left || !node.left.object || !node.left.object.object) {
+      MethodDefinition(node) {
+        if (node.kind === 'constructor') {
+          inConstructor = true;
+        }
+      },
+
+      AssignmentExpression(node) {
+        let item;
+        if (inConstructor || !node.left || !node.left.object || !node.left.object.object) {
           return;
         }
         item = node.left.object;
@@ -64,26 +71,32 @@ module.exports = {
           item.object.type === 'ThisExpression' &&
           item.property.name === 'state'
         ) {
-          var component = components.get(utils.getParentComponent());
-          var mutations = component && component.mutations || [];
+          const component = components.get(utils.getParentComponent());
+          const mutations = (component && component.mutations) || [];
           mutations.push(node.left.object);
           components.set(node, {
             mutateSetState: true,
-            mutations: mutations
+            mutations
           });
         }
       },
 
-      'Program:exit': function() {
-        var list = components.list();
-        for (var component in list) {
-          if (!has(list, component) || isValid(list[component])) {
-            continue;
-          }
-          reportMutations(list[component]);
+      'MethodDefinition:exit': function (node) {
+        if (node.kind === 'constructor') {
+          inConstructor = false;
         }
+      },
+
+      'Program:exit': function () {
+        const list = components.list();
+
+        Object.keys(list).forEach((key) => {
+          if (isValid(list[key])) {
+            return;
+          }
+          reportMutations(list[key]);
+        });
       }
     };
-
   })
 };

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

@@ -61,6 +61,14 @@ ruleTester.run('no-direct-mutation-state', rule, {
       '  }',
       '}'
     ].join('\n')
+  }, {
+    code: [
+      'class Hello extends React.Component {',
+      '  constructor() {',
+      '    this.state.foo = "bar"',
+      '  }',
+      '}'
+    ].join('\n')
   }],
 
   invalid: [{