fix(theme-classic): inconsistent code block wrapping (#7485)

Co-authored-by: sebastienlorber <lorber.sebastien@gmail.com>

packages/docusaurus-theme-common/src/contexts/navbarSecondaryMenu/content.tsx

@@ -9,11 +9,10 @@ import React, {
   useState,
   useContext,
   useEffect,
-  useMemo,
   type ReactNode,
   type ComponentType,
 } from 'react';
-import {ReactContextError} from '../../utils/reactUtils';
+import {ReactContextError, useShallowMemoObject} from '../../utils/reactUtils';
 
 // This context represents a "global layout store". A component (usually a
 // layout component) can request filling this store through
@@ -61,15 +60,6 @@ export function useNavbarSecondaryMenuContent(): Content {
   return value[0];
 }
 
-function useShallowMemoizedObject<O>(obj: O) {
-  return useMemo(
-    () => obj,
-    // Is this safe?
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-    [...Object.keys(obj), ...Object.values(obj)],
-  );
-}
-
 /**
  * This component renders nothing by itself, but it fills the placeholder in the
  * generic secondary menu layout. This reduces coupling between the main layout
@@ -94,7 +84,7 @@ export function NavbarSecondaryMenuFiller<P extends object>({
   const [, setContent] = context;
 
   // To avoid useless context re-renders, props are memoized shallowly
-  const memoizedProps = useShallowMemoizedObject(props);
+  const memoizedProps = useShallowMemoObject(props);
 
   useEffect(() => {
     // @ts-expect-error: this context is hard to type

packages/docusaurus-theme-common/src/hooks/useCodeWordWrap.ts

@@ -4,9 +4,53 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  */
-
 import type {RefObject} from 'react';
 import {useState, useCallback, useEffect, useRef} from 'react';
+import {useMutationObserver} from './useMutationObserver';
+
+// Callback fires when the "hidden" attribute of a tabpanel changes
+// See https://github.com/facebook/docusaurus/pull/7485
+function useTabBecameVisibleCallback(
+  codeBlockRef: RefObject<HTMLPreElement>,
+  callback: () => void,
+) {
+  const [hiddenTabElement, setHiddenTabElement] = useState<
+    Element | null | undefined
+  >();
+
+  const updateHiddenTabElement = useCallback(() => {
+    // No need to observe non-hidden tabs
+    // + we want to force a re-render when a tab becomes visible
+    setHiddenTabElement(
+      codeBlockRef.current?.closest('[role=tabpanel][hidden]'),
+    );
+  }, [codeBlockRef, setHiddenTabElement]);
+
+  useEffect(() => {
+    updateHiddenTabElement();
+  }, [updateHiddenTabElement]);
+
+  useMutationObserver(
+    hiddenTabElement,
+    (mutations: MutationRecord[]) => {
+      mutations.forEach((mutation) => {
+        if (
+          mutation.type === 'attributes' &&
+          mutation.attributeName === 'hidden'
+        ) {
+          callback();
+          updateHiddenTabElement();
+        }
+      });
+    },
+    {
+      attributes: true,
+      characterData: false,
+      childList: false,
+      subtree: false,
+    },
+  );
+}
 
 export function useCodeWordWrap(): {
   readonly codeBlockRef: RefObject<HTMLPreElement>;
@@ -38,6 +82,8 @@ export function useCodeWordWrap(): {
     setIsCodeScrollable(isScrollable);
   }, [codeBlockRef]);
 
+  useTabBecameVisibleCallback(codeBlockRef, updateCodeIsScrollable);
+
   useEffect(() => {
     updateCodeIsScrollable();
   }, [isEnabled, updateCodeIsScrollable]);

packages/docusaurus-theme-common/src/hooks/useMutationObserver.ts

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+import {useEffect} from 'react';
+import {useDynamicCallback, useShallowMemoObject} from '../utils/reactUtils';
+
+type Options = MutationObserverInit;
+
+const DefaultOptions: Options = {
+  attributes: true,
+  characterData: true,
+  childList: true,
+  subtree: true,
+};
+
+export function useMutationObserver(
+  target: Element | undefined | null,
+  callback: MutationCallback,
+  options: Options = DefaultOptions,
+): void {
+  const stableCallback = useDynamicCallback(callback);
+
+  // MutationObserver options are not nested much
+  // so this should be to memo options in 99%
+  // TODO handle options.attributeFilter array
+  const stableOptions: Options = useShallowMemoObject(options);
+
+  useEffect(() => {
+    const observer = new MutationObserver(stableCallback);
+    if (target) {
+      observer.observe(target, stableOptions);
+    }
+    return () => observer.disconnect();
+  }, [target, stableCallback, stableOptions]);
+}

packages/docusaurus-theme-common/src/utils/__tests__/reactUtils.test.ts

@@ -6,7 +6,7 @@
  */
 
 import {renderHook} from '@testing-library/react-hooks';
-import {usePrevious} from '../reactUtils';
+import {usePrevious, useShallowMemoObject} from '../reactUtils';
 
 describe('usePrevious', () => {
   it('returns the previous value of a variable', () => {
@@ -20,3 +20,37 @@ describe('usePrevious', () => {
     expect(result.current).toBe(2);
   });
 });
+
+describe('useShallowMemoObject', () => {
+  it('can memoize object', () => {
+    const someObj = {hello: 'world'};
+    const someArray = ['hello', 'world'];
+
+    const obj1 = {a: 1, b: '2', someObj, someArray};
+    const {result, rerender} = renderHook((val) => useShallowMemoObject(val), {
+      initialProps: obj1,
+    });
+    expect(result.current).toBe(obj1);
+
+    const obj2 = {a: 1, b: '2', someObj, someArray};
+    rerender(obj2);
+    expect(result.current).toBe(obj1);
+
+    const obj3 = {a: 1, b: '2', someObj, someArray};
+    rerender(obj3);
+    expect(result.current).toBe(obj1);
+
+    // Current implementation is basic and sensitive to order
+    const obj4 = {b: '2', a: 1, someObj, someArray};
+    rerender(obj4);
+    expect(result.current).toBe(obj4);
+
+    const obj5 = {b: '2', a: 1, someObj, someArray};
+    rerender(obj5);
+    expect(result.current).toBe(obj4);
+
+    const obj6 = {b: '2', a: 1, someObj: {...someObj}, someArray};
+    rerender(obj6);
+    expect(result.current).toBe(obj6);
+  });
+});

packages/docusaurus-theme-common/src/utils/reactUtils.tsx

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {useCallback, useEffect, useLayoutEffect, useRef} from 'react';
+import {useCallback, useEffect, useLayoutEffect, useMemo, useRef} from 'react';
 import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
 
 /**
@@ -74,3 +74,23 @@ export class ReactContextError extends Error {
     } is called outside the <${providerName}>. ${additionalInfo ?? ''}`;
   }
 }
+
+/**
+ * Shallow-memoize an object
+ *
+ * This means the returned object will be the same as the previous render
+ * if the attribute names and identities did not change.
+ *
+ * This works for simple cases: when attributes are primitives or stable objects
+ *
+ * @param obj
+ */
+export function useShallowMemoObject<O>(obj: O): O {
+  return useMemo(
+    () => obj,
+    // Is this safe?
+    // TODO make this implementation not order-dependent?
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [...Object.keys(obj), ...Object.values(obj)],
+  );
+}