Add stack addendum to invalid element type warning

- Show stack of element if element’s _source available (`in Unknown (at
file.js:10)
- Show parent’s generated stack when no _source available (since `in
Unknown` is useless)

src/isomorphic/classic/element/ReactElementValidator.js

@@ -184,24 +184,31 @@ function validatePropTypes(element) {
 var ReactElementValidator = {
 
   createElement: function(type, props, children) {
+    var element = ReactElement.createElement.apply(this, arguments);
+
     var validType =
       typeof type === 'string' ||
       typeof type === 'function' ||
       type !== null && typeof type === 'object' && typeof type.tag === 'number';
     // We warn in this case but don't throw. We expect the element creation to
     // succeed and there will likely be errors in render.
     if (!validType) {
+      var info = '';
+      if (element._source !== null) {
+        info = ReactComponentTreeHook.getCurrentStackAddendum(element);
+      } else {
+        info = ReactComponentTreeHook.getCurrentStackAddendum();
+      }
       warning(
         false,
         'React.createElement: type should not be null, undefined, boolean, or ' +
           'number. It should be a string (for DOM elements) or a ReactClass ' +
-          '(for composite components).%s',
-        getDeclarationErrorAddendum()
+          '(for composite components).%s%s',
+        getDeclarationErrorAddendum(),
+        info
       );
     }
 
-    var element = ReactElement.createElement.apply(this, arguments);
-
     // The result can be nullish if a mock or a custom function is used.
     // TODO: Drop this when these are no longer allowed as the type argument.
     if (element == null) {

src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js

@@ -339,7 +339,8 @@ describe('ReactElementValidator', () => {
       'Warning: React.createElement: type should not be null, undefined, ' +
       'boolean, or number. It should be a string (for DOM elements) or a ' +
       'ReactClass (for composite components). Check the render method of ' +
-      '`ParentComp`.'
+      '`ParentComp`.' +
+      '\n    in ParentComp'
     );
   });
 
@@ -535,12 +536,21 @@ describe('ReactElementValidator', () => {
     spyOn(console, 'error');
     var Foo = undefined;
     void <Foo>{[<div />]}</Foo>;
+
+    var info = console.error.calls.argsFor(0)[0];
+    var lines = info.split('\n');
+
     expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toBe(
+    expectDev(lines.length).toBe(2);
+    expectDev(lines[0]).toBe(
       'Warning: React.createElement: type should not be null, undefined, ' +
       'boolean, or number. It should be a string (for DOM elements) or a ' +
       'ReactClass (for composite components).'
     );
+    // The format is '    in Unknown (at ReactElementValidator-test.js:539)'
+    expectDev(lines[1]).toMatch(
+      /in Unknown \(at ReactElementValidator-test\.js\:\d+\)/
+    );
   });
 
 });

src/isomorphic/hooks/ReactComponentTreeHook.js

@@ -169,6 +169,8 @@ function getDisplayName(element: ?ReactElement): string {
     return '#text';
   } else if (typeof element.type === 'string') {
     return element.type;
+  } else if (element.type === null || typeof element.type === 'undefined') {
+    return 'Unknown';
   } else {
     return element.type.displayName || element.type.name || 'Unknown';
   }