[Fix] jsx-max-depth: avoid a crash

Fixes #2102.

Author: ljharb

lib/rules/jsx-max-depth.js

@@ -89,7 +89,7 @@ module.exports = {
 
             return jsxUtil.isJSX(writeExpr)
               && writeExpr
-              || writeExpr.type === 'Identifier'
+              || (writeExpr && writeExpr.type === 'Identifier')
               && findJSXElementOrFragment(variables, writeExpr.name);
           }
         }
@@ -103,7 +103,7 @@ module.exports = {
 
     function checkDescendant(baseDepth, children) {
       baseDepth++;
-      children.forEach(node => {
+      (children || []).forEach(node => {
         if (!hasJSX(node)) {
           return;
         }

lib/util/jsx.js

@@ -31,7 +31,7 @@ function isDOMComponent(node) {
  * @returns {boolean} Whether or not the node if a JSX element or fragment.
  */
 function isJSX(node) {
-  return ['JSXElement', 'JSXFragment'].indexOf(node.type) >= 0;
+  return node && ['JSXElement', 'JSXFragment'].indexOf(node.type) >= 0;
 }
 
 module.exports = {

tests/lib/rules/jsx-max-depth.js

@@ -94,6 +94,15 @@ ruleTester.run('jsx-max-depth', rule, {
       </tbody>
     `,
     options: [{max: 2}]
+  }, {
+    code: [
+      'const Example = props => {',
+      '  for (let i = 0; i < length; i++) {',
+      '    return <Text key={i} />;',
+      '  }',
+      '};'
+    ].join('\n'),
+    options: [{max: 1}]
   }],
 
   invalid: [{