From 73962c36645171a7a897bb0fb58e3442d0bb6bc9 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 23 Jan 2019 19:12:18 +0000
Subject: [PATCH] Revert "Revert "Double-render function components with Hooks
 in DEV in StrictMode" (#14652)" (#14654)

This reverts commit 3fbebb2a0b3b806f428c4154700af8e75e561895.
---
 .../src/ReactFiberBeginWork.js                |  53 +++++
 .../src/__tests__/ReactHooks-test.internal.js | 220 ++++++++++++++++++
 2 files changed, 273 insertions(+)

diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 5fc0fcc871426..9c4a72b7fedcb 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -250,6 +250,23 @@ function updateForwardRef(
       ref,
       renderExpirationTime,
     );
+    if (
+      debugRenderPhaseSideEffects ||
+      (debugRenderPhaseSideEffectsForStrictMode &&
+        workInProgress.mode & StrictMode)
+    ) {
+      // Only double-render components with Hooks
+      if (workInProgress.memoizedState !== null) {
+        renderWithHooks(
+          current,
+          workInProgress,
+          render,
+          nextProps,
+          ref,
+          renderExpirationTime,
+        );
+      }
+    }
     setCurrentPhase(null);
   } else {
     nextChildren = renderWithHooks(
@@ -543,6 +560,23 @@ function updateFunctionComponent(
       context,
       renderExpirationTime,
     );
+    if (
+      debugRenderPhaseSideEffects ||
+      (debugRenderPhaseSideEffectsForStrictMode &&
+        workInProgress.mode & StrictMode)
+    ) {
+      // Only double-render components with Hooks
+      if (workInProgress.memoizedState !== null) {
+        renderWithHooks(
+          current,
+          workInProgress,
+          Component,
+          nextProps,
+          context,
+          renderExpirationTime,
+        );
+      }
+    }
     setCurrentPhase(null);
   } else {
     nextChildren = renderWithHooks(
@@ -1210,6 +1244,25 @@ function mountIndeterminateComponent(
   } else {
     // Proceed under the assumption that this is a function component
     workInProgress.tag = FunctionComponent;
+    if (__DEV__) {
+      if (
+        debugRenderPhaseSideEffects ||
+        (debugRenderPhaseSideEffectsForStrictMode &&
+          workInProgress.mode & StrictMode)
+      ) {
+        // Only double-render components with Hooks
+        if (workInProgress.memoizedState !== null) {
+          renderWithHooks(
+            null,
+            workInProgress,
+            Component,
+            props,
+            context,
+            renderExpirationTime,
+          );
+        }
+      }
+    }
     reconcileChildren(null, workInProgress, value, renderExpirationTime);
     if (__DEV__) {
       validateFunctionComponentInDev(workInProgress, Component);
diff --git a/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js b/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
index bf4483986313e..e7c43ce274233 100644
--- a/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
@@ -841,6 +841,226 @@ describe('ReactHooks', () => {
     );
   });
 
+  it('double-invokes components with Hooks in Strict Mode', () => {
+    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = true;
+
+    const {useState, StrictMode} = React;
+    let renderCount = 0;
+
+    function NoHooks() {
+      renderCount++;
+      return <div />;
+    }
+
+    function HasHooks() {
+      useState(0);
+      renderCount++;
+      return <div />;
+    }
+
+    const FwdRef = React.forwardRef((props, ref) => {
+      renderCount++;
+      return <div />;
+    });
+
+    const FwdRefHasHooks = React.forwardRef((props, ref) => {
+      useState(0);
+      renderCount++;
+      return <div />;
+    });
+
+    const Memo = React.memo(props => {
+      renderCount++;
+      return <div />;
+    });
+
+    const MemoHasHooks = React.memo(props => {
+      useState(0);
+      renderCount++;
+      return <div />;
+    });
+
+    function Factory() {
+      return {
+        state: {},
+        render() {
+          renderCount++;
+          return <div />;
+        },
+      };
+    }
+
+    let renderer = ReactTestRenderer.create(null);
+
+    renderCount = 0;
+    renderer.update(<NoHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<NoHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <NoHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <NoHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+
+    renderCount = 0;
+    renderer.update(<FwdRef />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<FwdRef />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <FwdRef />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <FwdRef />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+
+    renderCount = 0;
+    renderer.update(<Memo arg={1} />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<Memo arg={2} />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <Memo arg={1} />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <Memo arg={2} />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(1);
+
+    renderCount = 0;
+    renderer.update(<Factory />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<Factory />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <Factory />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Treated like a class
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <Factory />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Treated like a class
+
+    renderCount = 0;
+    renderer.update(<HasHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<HasHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <HasHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <HasHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+
+    renderCount = 0;
+    renderer.update(<FwdRefHasHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<FwdRefHasHooks />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <FwdRefHasHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <FwdRefHasHooks />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+
+    renderCount = 0;
+    renderer.update(<MemoHasHooks arg={1} />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(<MemoHasHooks arg={2} />);
+    expect(renderCount).toBe(1);
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <MemoHasHooks arg={1} />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+    renderCount = 0;
+    renderer.update(
+      <StrictMode>
+        <MemoHasHooks arg={2} />
+      </StrictMode>,
+    );
+    expect(renderCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+  });
+
+  it('double-invokes useMemo in DEV StrictMode despite []', () => {
+    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = true;
+    const {useMemo, StrictMode} = React;
+
+    let useMemoCount = 0;
+    function BadUseMemo() {
+      useMemo(() => {
+        useMemoCount++;
+      }, []);
+      return <div />;
+    }
+
+    useMemoCount = 0;
+    ReactTestRenderer.create(
+      <StrictMode>
+        <BadUseMemo />
+      </StrictMode>,
+    );
+    expect(useMemoCount).toBe(__DEV__ ? 2 : 1); // Has Hooks
+  });
+
   it('warns on using differently ordered hooks on subsequent renders', () => {
     const {useState, useReducer} = React;
     function useCustomHook() {