Double-render function components with Hooks in DEV in StrictMode (#1…

…4643)

* Double-render functions in strict mode

* Double-invoke first function component render too

* Mark TestRendererAsync test as internal and revert changes to it

TestRenderer is built with strict mode doublerender off.

We could change that but I'm not sure we want to. So I'll just flip the flag off for this test.

* Only double-invoke components using Hooks

* Revert unintentional change

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(
@@ -1207,6 +1241,25 @@ 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);

packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js

@@ -660,4 +660,224 @@ describe('ReactHooks', () => {
       'Hooks can only be called inside the body of a function component',
     );
   });
+
+  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
+  });
 });