Always use the second result

Author: gaearon

packages/react-reconciler/src/ReactFiberClassComponent.new.js

@@ -169,21 +169,21 @@ function applyDerivedStateFromProps(
   nextProps: any,
 ) {
   const prevState = workInProgress.memoizedState;
-  const partialState = getDerivedStateFromProps(nextProps, prevState);
+  let partialState = getDerivedStateFromProps(nextProps, prevState);
   if (__DEV__) {
-    warnOnUndefinedDerivedState(ctor, partialState);
     if (
       debugRenderPhaseSideEffectsForStrictMode &&
       workInProgress.mode & StrictLegacyMode
     ) {
       disableLogs();
       try {
         // Invoke the function an extra time to help detect side-effects.
-        getDerivedStateFromProps(nextProps, prevState);
+        partialState = getDerivedStateFromProps(nextProps, prevState);
       } finally {
         reenableLogs();
       }
     }
+    warnOnUndefinedDerivedState(ctor, partialState);
   }
   // Merge the partial state and the previous state.
   const memoizedState =
@@ -318,7 +318,7 @@ function checkShouldComponentUpdate(
 ) {
   const instance = workInProgress.stateNode;
   if (typeof instance.shouldComponentUpdate === 'function') {
-    const shouldUpdate = instance.shouldComponentUpdate(
+    let shouldUpdate = instance.shouldComponentUpdate(
       newProps,
       newState,
       nextContext,
@@ -338,7 +338,11 @@ function checkShouldComponentUpdate(
         disableLogs();
         try {
           // Invoke the function an extra time to help detect side-effects.
-          instance.shouldComponentUpdate(newProps, newState, nextContext);
+          shouldUpdate = instance.shouldComponentUpdate(
+            newProps,
+            newState,
+            nextContext,
+          );
         } finally {
           reenableLogs();
         }
@@ -651,7 +655,7 @@ function constructClassInstance(
       : emptyContextObject;
   }
 
-  const instance = new ctor(props, context);
+  let instance = new ctor(props, context);
   // Instantiate twice to help detect side-effects.
   if (__DEV__) {
     if (
@@ -660,7 +664,7 @@ function constructClassInstance(
     ) {
       disableLogs();
       try {
-        new ctor(props, context); // eslint-disable-line no-new
+        instance = new ctor(props, context); // eslint-disable-line no-new
       } finally {
         reenableLogs();
       }

packages/react-reconciler/src/ReactFiberClassComponent.old.js

@@ -169,21 +169,21 @@ function applyDerivedStateFromProps(
   nextProps: any,
 ) {
   const prevState = workInProgress.memoizedState;
-  const partialState = getDerivedStateFromProps(nextProps, prevState);
+  let partialState = getDerivedStateFromProps(nextProps, prevState);
   if (__DEV__) {
-    warnOnUndefinedDerivedState(ctor, partialState);
     if (
       debugRenderPhaseSideEffectsForStrictMode &&
       workInProgress.mode & StrictLegacyMode
     ) {
       disableLogs();
       try {
         // Invoke the function an extra time to help detect side-effects.
-        getDerivedStateFromProps(nextProps, prevState);
+        partialState = getDerivedStateFromProps(nextProps, prevState);
       } finally {
         reenableLogs();
       }
     }
+    warnOnUndefinedDerivedState(ctor, partialState);
   }
   // Merge the partial state and the previous state.
   const memoizedState =
@@ -318,7 +318,7 @@ function checkShouldComponentUpdate(
 ) {
   const instance = workInProgress.stateNode;
   if (typeof instance.shouldComponentUpdate === 'function') {
-    const shouldUpdate = instance.shouldComponentUpdate(
+    let shouldUpdate = instance.shouldComponentUpdate(
       newProps,
       newState,
       nextContext,
@@ -338,7 +338,11 @@ function checkShouldComponentUpdate(
         disableLogs();
         try {
           // Invoke the function an extra time to help detect side-effects.
-          instance.shouldComponentUpdate(newProps, newState, nextContext);
+          shouldUpdate = instance.shouldComponentUpdate(
+            newProps,
+            newState,
+            nextContext,
+          );
         } finally {
           reenableLogs();
         }
@@ -651,7 +655,7 @@ function constructClassInstance(
       : emptyContextObject;
   }
 
-  const instance = new ctor(props, context);
+  let instance = new ctor(props, context);
   // Instantiate twice to help detect side-effects.
   if (__DEV__) {
     if (
@@ -660,7 +664,7 @@ function constructClassInstance(
     ) {
       disableLogs();
       try {
-        new ctor(props, context); // eslint-disable-line no-new
+        instance = new ctor(props, context); // eslint-disable-line no-new
       } finally {
         reenableLogs();
       }