From 8d5a147b79cd80d2f52ada5b286d24ad6f7fbf01 Mon Sep 17 00:00:00 2001
From: Dan Abramov <gaearon@fb.com>
Date: Wed, 7 Jun 2017 21:28:02 +0100
Subject: [PATCH 1/2] Bail out on fibers that returned false from
 shouldComponentUpdate

---
 backend/ReactTypeOfSideEffect.js | 26 ++++++++++++++++++++++++++
 backend/attachRendererFiber.js   |  7 +++++++
 2 files changed, 33 insertions(+)
 create mode 100644 backend/ReactTypeOfSideEffect.js

diff --git a/backend/ReactTypeOfSideEffect.js b/backend/ReactTypeOfSideEffect.js
new file mode 100644
index 0000000000..ac089cb9c4
--- /dev/null
+++ b/backend/ReactTypeOfSideEffect.js
@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+// Copied from React repo.
+
+module.exports = {
+  NoEffect: 0, //           0b00000000
+  Bailout: 1, //            0b00000001
+  Placement: 2, //          0b00000010
+  Update: 4, //             0b00000100
+  PlacementAndUpdate: 6, // 0b00000110
+  Deletion: 8, //           0b00001000
+  ContentReset: 16, //      0b00010000
+  Callback: 32, //          0b00100000
+  Err: 64, //               0b01000000
+  Ref: 128, //              0b10000000
+};
diff --git a/backend/attachRendererFiber.js b/backend/attachRendererFiber.js
index 5a2a0b2898..d447738c33 100644
--- a/backend/attachRendererFiber.js
+++ b/backend/attachRendererFiber.js
@@ -16,6 +16,9 @@ var {
   ClassComponent,
   HostRoot,
 } = require('./ReactTypeOfWork');
+var {
+  Bailout,
+} = require('./ReactTypeOfSideEffect');
 
 function attachRendererFiber(hook: Hook, rid: string, renderer: ReactRenderer): Helpers {
   // This is a slightly annoying indirection.
@@ -39,6 +42,10 @@ function attachRendererFiber(hook: Hook, rid: string, renderer: ReactRenderer):
 
   function hasDataChanged(prevFiber, nextFiber) {
     if (prevFiber.tag === ClassComponent) {
+      // Skip subtrees that bailed out with shouldComponentUpdate.
+      if ((nextFiber.effectTag & Bailout) === Bailout) {
+        return false;
+      }
       // Only classes have context.
       if (prevFiber.stateNode.context !== nextFiber.stateNode.context) {
         return true;

From b397124db304309155b3f1777180ad47ca04d8ba Mon Sep 17 00:00:00 2001
From: Dan Abramov <gaearon@fb.com>
Date: Thu, 8 Jun 2017 21:18:41 +0100
Subject: [PATCH 2/2] Inline constant and flip flag to match React PR

---
 backend/ReactTypeOfSideEffect.js | 26 --------------------------
 backend/attachRendererFiber.js   | 12 +++++++-----
 2 files changed, 7 insertions(+), 31 deletions(-)
 delete mode 100644 backend/ReactTypeOfSideEffect.js

diff --git a/backend/ReactTypeOfSideEffect.js b/backend/ReactTypeOfSideEffect.js
deleted file mode 100644
index ac089cb9c4..0000000000
--- a/backend/ReactTypeOfSideEffect.js
+++ /dev/null
@@ -1,26 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
- */
-'use strict';
-
-// Copied from React repo.
-
-module.exports = {
-  NoEffect: 0, //           0b00000000
-  Bailout: 1, //            0b00000001
-  Placement: 2, //          0b00000010
-  Update: 4, //             0b00000100
-  PlacementAndUpdate: 6, // 0b00000110
-  Deletion: 8, //           0b00001000
-  ContentReset: 16, //      0b00010000
-  Callback: 32, //          0b00100000
-  Err: 64, //               0b01000000
-  Ref: 128, //              0b10000000
-};
diff --git a/backend/attachRendererFiber.js b/backend/attachRendererFiber.js
index d447738c33..c24c827536 100644
--- a/backend/attachRendererFiber.js
+++ b/backend/attachRendererFiber.js
@@ -16,9 +16,9 @@ var {
   ClassComponent,
   HostRoot,
 } = require('./ReactTypeOfWork');
-var {
-  Bailout,
-} = require('./ReactTypeOfSideEffect');
+
+// Inlined from ReactTypeOfSideEffect
+var PerformedWork = 1;
 
 function attachRendererFiber(hook: Hook, rid: string, renderer: ReactRenderer): Helpers {
   // This is a slightly annoying indirection.
@@ -42,10 +42,12 @@ function attachRendererFiber(hook: Hook, rid: string, renderer: ReactRenderer):
 
   function hasDataChanged(prevFiber, nextFiber) {
     if (prevFiber.tag === ClassComponent) {
-      // Skip subtrees that bailed out with shouldComponentUpdate.
-      if ((nextFiber.effectTag & Bailout) === Bailout) {
+      // Skip if the class performed no work (shouldComponentUpdate bailout).
+      // eslint-disable-next-line no-bitwise
+      if ((nextFiber.effectTag & PerformedWork) !== PerformedWork) {
         return false;
       }
+
       // Only classes have context.
       if (prevFiber.stateNode.context !== nextFiber.stateNode.context) {
         return true;