Mention actual prop type in element type checker (#7319)

(cherry picked from commit 8bcea5310e)

src/isomorphic/classic/types/ReactPropTypes.js

@@ -236,11 +236,13 @@ function createArrayOfTypeChecker(typeChecker) {
 
 function createElementTypeChecker() {
   function validate(props, propName, componentName, location, propFullName) {
-    if (!ReactElement.isValidElement(props[propName])) {
+    var propValue = props[propName];
+    if (!ReactElement.isValidElement(propValue)) {
       var locationName = ReactPropTypeLocationNames[location];
+      var propType = getPropType(propValue);
       return new Error(
-        `Invalid ${locationName} \`${propFullName}\` supplied to ` +
-        `\`${componentName}\`, expected a single ReactElement.`
+        `Invalid ${locationName} \`${propFullName}\` of type ` +
+        `\`${propType}\` supplied to \`${componentName}\`, expected a single ReactElement.`
       );
     }
     return null;

src/isomorphic/classic/types/__tests__/ReactPropTypes-test.js

@@ -356,12 +356,30 @@ describe('ReactPropTypes', function() {
     });
 
     it('should not support multiple components or scalar values', () => {
-      var message = 'Invalid prop `testProp` supplied to `testComponent`, ' +
-        'expected a single ReactElement.';
-      typeCheckFail(PropTypes.element, [<div />, <div />], message);
-      typeCheckFail(PropTypes.element, 123, message);
-      typeCheckFail(PropTypes.element, 'foo', message);
-      typeCheckFail(PropTypes.element, false, message);
+      typeCheckFail(
+        PropTypes.element,
+        [<div />, <div />],
+        'Invalid prop `testProp` of type `array` supplied to `testComponent`, ' +
+        'expected a single ReactElement.'
+      );
+      typeCheckFail(
+        PropTypes.element,
+        123,
+        'Invalid prop `testProp` of type `number` supplied to `testComponent`, ' +
+        'expected a single ReactElement.'
+      );
+      typeCheckFail(
+        PropTypes.element,
+        'foo',
+        'Invalid prop `testProp` of type `string` supplied to `testComponent`, ' +
+        'expected a single ReactElement.'
+      );
+      typeCheckFail(
+        PropTypes.element,
+        false,
+        'Invalid prop `testProp` of type `boolean` supplied to `testComponent`, ' +
+        'expected a single ReactElement.'
+      );
     });
 
     it('should be able to define a single child as label', () => {