From afbd59a742d412157e5d4bb86ab4cf33ca167698 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Fri, 18 Jan 2019 22:20:43 +0000
Subject: [PATCH 1/2] Fix handling of sync rejection

Reverts #14632 and adds a regression test.
---
 .../src/ReactFiberLazyComponent.js            |  2 +-
 .../src/__tests__/ReactLazy-test.internal.js  | 31 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/packages/react-reconciler/src/ReactFiberLazyComponent.js b/packages/react-reconciler/src/ReactFiberLazyComponent.js
index 07fd7a70762..179262fa449 100644
--- a/packages/react-reconciler/src/ReactFiberLazyComponent.js
+++ b/packages/react-reconciler/src/ReactFiberLazyComponent.js
@@ -47,6 +47,7 @@ export function readLazyComponentType<T>(lazyComponent: LazyComponent<T>): T {
       lazyComponent._status = Pending;
       const ctor = lazyComponent._ctor;
       const thenable = ctor();
+      lazyComponent._result = thenable;
       thenable.then(
         moduleObject => {
           if (lazyComponent._status === Pending) {
@@ -77,7 +78,6 @@ export function readLazyComponentType<T>(lazyComponent: LazyComponent<T>): T {
       if (lazyComponent._status === Resolved) {
         return lazyComponent._result;
       }
-      lazyComponent._result = thenable;
       throw thenable;
     }
   }
diff --git a/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js b/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
index 8fb4210f929..58460cc0928 100644
--- a/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
@@ -78,6 +78,37 @@ describe('ReactLazy', () => {
     expect(root).toMatchRenderedOutput('Hi');
   });
 
+  it('can handle synchronous thenable rejection', async () => {
+    const LazyText = lazy(() => ({
+      then(resolve, reject) {
+        reject(new Error('oh no'));
+      },
+    }));
+
+    class ErrorBoundary extends React.Component {
+      state = {};
+      static getDerivedStateFromError(error) {
+        return {message: error.message};
+      }
+      render() {
+        return this.state.message
+          ? `Error: ${this.state.message}`
+          : this.props.children;
+      }
+    }
+
+    const root = ReactTestRenderer.create(
+      <ErrorBoundary>
+        <Suspense fallback={<Text text="Loading..." />}>
+          <LazyText text="Hi" />
+        </Suspense>
+      </ErrorBoundary>,
+    );
+    // TODO: ideally we could make it skip this commit.
+    expect(ReactTestRenderer).toHaveYielded(['Loading...']);
+    expect(root).toMatchRenderedOutput('Error: oh no');
+  });
+
   it('multiple lazy components', async () => {
     function Foo() {
       return <Text text="Foo" />;

From 842d1e2e57bc6c63ead4bf55aaa83f5b0fc13b27 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Fri, 18 Jan 2019 22:24:35 +0000
Subject: [PATCH 2/2] Handle rejection synchronously too

Fewer footguns and seems like nicer behavior anyway.
---
 .../react-reconciler/src/ReactFiberLazyComponent.js   | 11 +++++++----
 .../src/__tests__/ReactLazy-test.internal.js          |  5 ++---
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/packages/react-reconciler/src/ReactFiberLazyComponent.js b/packages/react-reconciler/src/ReactFiberLazyComponent.js
index 179262fa449..1db5ecd35ca 100644
--- a/packages/react-reconciler/src/ReactFiberLazyComponent.js
+++ b/packages/react-reconciler/src/ReactFiberLazyComponent.js
@@ -47,7 +47,6 @@ export function readLazyComponentType<T>(lazyComponent: LazyComponent<T>): T {
       lazyComponent._status = Pending;
       const ctor = lazyComponent._ctor;
       const thenable = ctor();
-      lazyComponent._result = thenable;
       thenable.then(
         moduleObject => {
           if (lazyComponent._status === Pending) {
@@ -74,10 +73,14 @@ export function readLazyComponentType<T>(lazyComponent: LazyComponent<T>): T {
           }
         },
       );
-      // Check if it resolved synchronously
-      if (lazyComponent._status === Resolved) {
-        return lazyComponent._result;
+      // Handle synchronous thenables.
+      switch (lazyComponent._status) {
+        case Resolved:
+          return lazyComponent._result;
+        case Rejected:
+          throw lazyComponent._result;
       }
+      lazyComponent._result = thenable;
       throw thenable;
     }
   }
diff --git a/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js b/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
index 58460cc0928..4ce78581544 100644
--- a/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
@@ -78,7 +78,7 @@ describe('ReactLazy', () => {
     expect(root).toMatchRenderedOutput('Hi');
   });
 
-  it('can handle synchronous thenable rejection', async () => {
+  it('can reject synchronously without suspending', async () => {
     const LazyText = lazy(() => ({
       then(resolve, reject) {
         reject(new Error('oh no'));
@@ -104,8 +104,7 @@ describe('ReactLazy', () => {
         </Suspense>
       </ErrorBoundary>,
     );
-    // TODO: ideally we could make it skip this commit.
-    expect(ReactTestRenderer).toHaveYielded(['Loading...']);
+    expect(ReactTestRenderer).toHaveYielded([]);
     expect(root).toMatchRenderedOutput('Error: oh no');
   });