More helpful message when passing an element to createElement() (#13131)

* [#13130] Add a more helpful message when passing an element to createElement()

* better conditional flow

* update after review

* move last condition inside last else clause

* Added test case

* compare 25132typeof to REACT_ELEMENT_TYPE

* runs prettier

* remove unrelated changes

* Tweak the message

Author: DCtheTall

packages/react/src/ReactElementValidator.js

@@ -19,6 +19,7 @@ import {
   getIteratorFn,
   REACT_FORWARD_REF_TYPE,
   REACT_FRAGMENT_TYPE,
+  REACT_ELEMENT_TYPE,
 } from 'shared/ReactSymbols';
 import checkPropTypes from 'prop-types/checkPropTypes';
 import warning from 'shared/warning';
@@ -286,6 +287,10 @@ export function createElementWithValidation(type, props, children) {
       typeString = 'null';
     } else if (Array.isArray(type)) {
       typeString = 'array';
+    } else if (type !== undefined && type.$$typeof === REACT_ELEMENT_TYPE) {
+      typeString = `<${getComponentName(type.type) || 'Unknown'} />`;
+      info =
+        ' Did you accidentally export a JSX literal instead of a component?';
     } else {
       typeString = typeof type;
     }

packages/react/src/__tests__/ReactElementValidator-test.internal.js

@@ -229,12 +229,17 @@ describe('ReactElementValidator', () => {
   });
 
   it('gives a helpful error when passing invalid types', () => {
+    function Foo() {}
     expect(() => {
       React.createElement(undefined);
       React.createElement(null);
       React.createElement(true);
       React.createElement({x: 17});
       React.createElement({});
+      React.createElement(React.createElement('div'));
+      React.createElement(React.createElement(Foo));
+      React.createElement(React.createElement(React.createContext().Consumer));
+      React.createElement({$$typeof: 'non-react-thing'});
     }).toWarnDev(
       [
         'Warning: React.createElement: type is invalid -- expected a string ' +
@@ -256,6 +261,21 @@ describe('ReactElementValidator', () => {
           'components) but got: object. You likely forgot to export your ' +
           "component from the file it's defined in, or you might have mixed up " +
           'default and named imports.',
+        'Warning: React.createElement: type is invalid -- expected a string ' +
+          '(for built-in components) or a class/function (for composite ' +
+          'components) but got: <div />. Did you accidentally export a JSX literal ' +
+          'instead of a component?',
+        'Warning: React.createElement: type is invalid -- expected a string ' +
+          '(for built-in components) or a class/function (for composite ' +
+          'components) but got: <Foo />. Did you accidentally export a JSX literal ' +
+          'instead of a component?',
+        'Warning: React.createElement: type is invalid -- expected a string ' +
+          '(for built-in components) or a class/function (for composite ' +
+          'components) but got: <Context.Consumer />. Did you accidentally ' +
+          'export a JSX literal instead of a component?',
+        'Warning: React.createElement: type is invalid -- expected a string ' +
+          '(for built-in components) or a class/function (for composite ' +
+          'components) but got: object.',
       ],
       {withoutStack: true},
     );