From 404a1d022ab0f450d70885e9fe0ab105a485109e Mon Sep 17 00:00:00 2001
From: Brian Vaughn <bvaughn@fb.com>
Date: Thu, 6 Aug 2020 14:50:05 -0400
Subject: [PATCH] Warn about undefined return value for memo and forwardRef

---
 .../src/__tests__/ReactEmptyComponent-test.js | 20 +++++++++++++++++++
 .../src/ReactChildFiber.new.js                | 10 +++++++---
 .../src/ReactChildFiber.old.js                | 10 +++++++---
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/packages/react-dom/src/__tests__/ReactEmptyComponent-test.js b/packages/react-dom/src/__tests__/ReactEmptyComponent-test.js
index 10e95f7cf7ba..0c0b1d1a9273 100644
--- a/packages/react-dom/src/__tests__/ReactEmptyComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactEmptyComponent-test.js
@@ -316,4 +316,24 @@ describe('ReactEmptyComponent', () => {
     const noscript2 = container.firstChild;
     expect(noscript2).toBe(null);
   });
+
+  it('should warn about React.forwardRef that returns undefined', () => {
+    const Empty = () => {};
+    const EmptyForwardRef = React.forwardRef(Empty);
+
+    expect(() => {
+      ReactTestUtils.renderIntoDocument(<EmptyForwardRef />);
+    }).toThrowError(
+      'ForwardRef(Empty)(...): Nothing was returned from render.',
+    );
+  });
+
+  it('should warn about React.memo that returns undefined', () => {
+    const Empty = () => {};
+    const EmptyMemo = React.memo(Empty);
+
+    expect(() => {
+      ReactTestUtils.renderIntoDocument(<EmptyMemo />);
+    }).toThrowError('Empty(...): Nothing was returned from render.');
+  });
 });
diff --git a/packages/react-reconciler/src/ReactChildFiber.new.js b/packages/react-reconciler/src/ReactChildFiber.new.js
index e39660ba0b56..3bef3545fc3a 100644
--- a/packages/react-reconciler/src/ReactChildFiber.new.js
+++ b/packages/react-reconciler/src/ReactChildFiber.new.js
@@ -29,7 +29,9 @@ import {
   ClassComponent,
   HostText,
   HostPortal,
+  ForwardRef,
   Fragment,
+  SimpleMemoComponent,
   Block,
 } from './ReactWorkTags';
 import invariant from 'shared/invariant';
@@ -1393,14 +1395,16 @@ function ChildReconciler(shouldTrackSideEffects) {
         // Intentionally fall through to the next case, which handles both
         // functions and classes
         // eslint-disable-next-lined no-fallthrough
-        case FunctionComponent: {
-          const Component = returnFiber.type;
+        case Block:
+        case FunctionComponent:
+        case ForwardRef:
+        case SimpleMemoComponent: {
           invariant(
             false,
             '%s(...): Nothing was returned from render. This usually means a ' +
               'return statement is missing. Or, to render nothing, ' +
               'return null.',
-            Component.displayName || Component.name || 'Component',
+            getComponentName(returnFiber.type) || 'Component',
           );
         }
       }
diff --git a/packages/react-reconciler/src/ReactChildFiber.old.js b/packages/react-reconciler/src/ReactChildFiber.old.js
index fc597b0a7d36..6af9a6ab9fee 100644
--- a/packages/react-reconciler/src/ReactChildFiber.old.js
+++ b/packages/react-reconciler/src/ReactChildFiber.old.js
@@ -29,7 +29,9 @@ import {
   ClassComponent,
   HostText,
   HostPortal,
+  ForwardRef,
   Fragment,
+  SimpleMemoComponent,
   Block,
 } from './ReactWorkTags';
 import invariant from 'shared/invariant';
@@ -1385,14 +1387,16 @@ function ChildReconciler(shouldTrackSideEffects) {
         // Intentionally fall through to the next case, which handles both
         // functions and classes
         // eslint-disable-next-lined no-fallthrough
-        case FunctionComponent: {
-          const Component = returnFiber.type;
+        case Block:
+        case FunctionComponent:
+        case ForwardRef:
+        case SimpleMemoComponent: {
           invariant(
             false,
             '%s(...): Nothing was returned from render. This usually means a ' +
               'return statement is missing. Or, to render nothing, ' +
               'return null.',
-            Component.displayName || Component.name || 'Component',
+            getComponentName(returnFiber.type) || 'Component',
           );
         }
       }