From 10ae68a73cb57132651b0f698890e787386d6b5f Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@me.com>
Date: Tue, 30 Jun 2020 16:08:49 +0100
Subject: [PATCH 1/2] Fix development mode hang when iframe is removed

---
 packages/shared/invokeGuardedCallbackImpl.js | 28 ++++++++++++++++----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/packages/shared/invokeGuardedCallbackImpl.js b/packages/shared/invokeGuardedCallbackImpl.js
index 8ba03aa8d9dd..117663abc1f8 100644
--- a/packages/shared/invokeGuardedCallbackImpl.js
+++ b/packages/shared/invokeGuardedCallbackImpl.js
@@ -9,7 +9,7 @@
 
 import invariant from 'shared/invariant';
 
-let invokeGuardedCallbackImpl = function<A, B, C, D, E, F, Context>(
+function invokeGuardedCallbackProd<A, B, C, D, E, F, Context>(
   name: string | null,
   func: (a: A, b: B, c: C, d: D, e: E, f: F) => mixed,
   context: Context,
@@ -26,7 +26,9 @@ let invokeGuardedCallbackImpl = function<A, B, C, D, E, F, Context>(
   } catch (error) {
     this.onError(error);
   }
-};
+}
+
+let invokeGuardedCallbackImpl = invokeGuardedCallbackProd;
 
 if (__DEV__) {
   // In DEV mode, we swap out invokeGuardedCallback for a special version
@@ -58,7 +60,15 @@ if (__DEV__) {
   ) {
     const fakeNode = document.createElement('react');
 
-    const invokeGuardedCallbackDev = function<A, B, C, D, E, F, Context>(
+    invokeGuardedCallbackImpl = function invokeGuardedCallbackDev<
+      A,
+      B,
+      C,
+      D,
+      E,
+      F,
+      Context,
+    >(
       name: string | null,
       func: (a: A, b: B, c: C, d: D, e: E, f: F) => mixed,
       context: Context,
@@ -85,6 +95,7 @@ if (__DEV__) {
       );
       const evt = document.createEvent('Event');
 
+      let didCall = false;
       // Keeps track of whether the user-provided callback threw an error. We
       // set this to true at the beginning, then set it to false right after
       // calling the function. If the function errors, `didError` will never be
@@ -110,6 +121,7 @@ if (__DEV__) {
       // call the user-provided callback.
       const funcArgs = Array.prototype.slice.call(arguments, 3);
       function callCallback() {
+        didCall = true;
         // We immediately remove the callback from event listeners so that
         // nested `invokeGuardedCallback` calls do not clash. Otherwise, a
         // nested call would trigger the fake event handlers of any call higher
@@ -208,9 +220,15 @@ if (__DEV__) {
 
       // Remove our event listeners
       window.removeEventListener('error', handleWindowError);
-    };
 
-    invokeGuardedCallbackImpl = invokeGuardedCallbackDev;
+      if (!didCall) {
+        // Something went really wrong, and our event was not dispatched.
+        // https://github.com/facebook/react/issues/16734
+        // https://github.com/facebook/react/issues/16585
+        // Fall back to the production implementation.
+        return invokeGuardedCallbackProd.apply(this, arguments);
+      }
+    };
   }
 }
 

From af5748830ecdf9add29dcb92c5db39015b2397ed Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@me.com>
Date: Tue, 30 Jun 2020 16:32:11 +0100
Subject: [PATCH 2/2] Also fix #16734

---
 packages/shared/invokeGuardedCallbackImpl.js | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/packages/shared/invokeGuardedCallbackImpl.js b/packages/shared/invokeGuardedCallbackImpl.js
index 117663abc1f8..60e32e0a5528 100644
--- a/packages/shared/invokeGuardedCallbackImpl.js
+++ b/packages/shared/invokeGuardedCallbackImpl.js
@@ -116,12 +116,7 @@ if (__DEV__) {
         'event',
       );
 
-      // Create an event handler for our fake event. We will synchronously
-      // dispatch our fake event using `dispatchEvent`. Inside the handler, we
-      // call the user-provided callback.
-      const funcArgs = Array.prototype.slice.call(arguments, 3);
-      function callCallback() {
-        didCall = true;
+      function restoreAfterDispatch() {
         // We immediately remove the callback from event listeners so that
         // nested `invokeGuardedCallback` calls do not clash. Otherwise, a
         // nested call would trigger the fake event handlers of any call higher
@@ -138,7 +133,15 @@ if (__DEV__) {
         ) {
           window.event = windowEvent;
         }
+      }
 
+      // Create an event handler for our fake event. We will synchronously
+      // dispatch our fake event using `dispatchEvent`. Inside the handler, we
+      // call the user-provided callback.
+      const funcArgs = Array.prototype.slice.call(arguments, 3);
+      function callCallback() {
+        didCall = true;
+        restoreAfterDispatch();
         func.apply(context, funcArgs);
         didError = false;
       }
@@ -195,7 +198,7 @@ if (__DEV__) {
         Object.defineProperty(window, 'event', windowEventDescriptor);
       }
 
-      if (didError) {
+      if (didCall && didError) {
         if (!didSetError) {
           // The callback errored, but the error event never fired.
           error = new Error(
@@ -226,6 +229,7 @@ if (__DEV__) {
         // https://github.com/facebook/react/issues/16734
         // https://github.com/facebook/react/issues/16585
         // Fall back to the production implementation.
+        restoreAfterDispatch();
         return invokeGuardedCallbackProd.apply(this, arguments);
       }
     };