Ignore jsx-key if inside React.Children.toArray()

jsx-key rule should always succeed if we're inside
React.Children.toArray() because omitting the key there doesn't cause a
React warning.

Fixes jsx-eslint#1574.

Author: silvenon

lib/rules/jsx-key.js

@@ -36,8 +36,31 @@ module.exports = {
       return body.filter(item => item.type === 'ReturnStatement')[0];
     }
 
+    const childrenToArraySelector = `:matches(
+      CallExpression
+        [callee.object.object.name=React]
+        [callee.object.property.name=Children]
+        [callee.property.name=toArray],
+      CallExpression
+        [callee.object.name=Children]
+        [callee.property.name=toArray]
+    )`.replace(/\s/g, '');
+    let isWithinChildrenToArray = false;
+
     return {
+      [childrenToArraySelector]: function() {
+        isWithinChildrenToArray = true;
+      },
+
+      [`${childrenToArraySelector}:exit`]: function() {
+        isWithinChildrenToArray = false;
+      },
+
       JSXElement: function(node) {
+        if (isWithinChildrenToArray) {
+          return;
+        }
+
         if (hasProp(node.openingElement.attributes, 'key')) {
           return;
         }
@@ -52,6 +75,10 @@ module.exports = {
 
       // Array.prototype.map
       CallExpression: function (node) {
+        if (isWithinChildrenToArray) {
+          return;
+        }
+
         if (node.callee && node.callee.type !== 'MemberExpression') {
           return;
         }

tests/lib/rules/jsx-key.js

@@ -37,7 +37,15 @@ ruleTester.run('jsx-key', rule, {
     {code: '[1, 2, 3].foo(x => <App />);'},
     {code: 'var App = () => <div />;'},
     {code: '[1, 2, 3].map(function(x) { return; });'},
-    {code: 'foo(() => <div />);'}
+    {code: 'foo(() => <div />);'},
+    // #1574
+    {code: 'React.Children.toArray([1, 2 ,3].map(x => <App />));'},
+    {
+      code: `
+      import { Children } from "react";
+      Children.toArray([1, 2 ,3].map(x => <App />));
+      `
+    }
   ],
   invalid: [{
     code: '[<App />];',