Add option for state-in-constructor rule

Author: lukyth

lib/rules/state-in-constructor.js

@@ -1,5 +1,5 @@
 /**
- * @fileoverview State initialization in an ES6 class component should be in a constructor
+ * @fileoverview Enforce the state initialization style to be either in a constructor or with a class property
  * @author Kanitkorn Sujautra
  */
 'use strict';
@@ -19,21 +19,41 @@ module.exports = {
       recommended: false,
       url: docsUrl('state-in-constructor')
     },
-    schema: []
+    schema: [{
+      enum: ['always', 'never']
+    }]
   },
 
-  create: Components.detect((context, components, utils) => ({
-    ClassProperty: function (node) {
-      if (
-        !node.static &&
-        node.key.name === 'state' &&
-        utils.isES6Component(node.parent.parent)
-      ) {
-        context.report({
-          node,
-          message: 'State initialization should be in a constructor'
-        });
+  create: Components.detect((context, components, utils) => {
+    const option = context.options[0] || 'always';
+    return {
+      ClassProperty: function (node) {
+        if (
+          option === 'always' &&
+          !node.static &&
+          node.key.name === 'state' &&
+          utils.isES6Component(node.parent.parent)
+        ) {
+          context.report({
+            node,
+            message: 'State initialization should be in a constructor'
+          });
+        }
+      },
+      AssignmentExpression(node) {
+        if (
+          option === 'never' &&
+          node.left.object.type === 'ThisExpression' &&
+          node.left.property.name === 'state' &&
+          node.parent.parent.parent.parent.kind === 'constructor' &&
+          utils.isES6Component(node.parent.parent.parent.parent.parent.parent)
+        ) {
+          context.report({
+            node,
+            message: 'State initialization should be in a class property'
+          });
+        }
       }
-    }
-  }))
+    };
+  })
 };