When clicking the sidebar caret, open the category index page if available

src/theme/DocSidebarItem/Category/index.tsx

@@ -0,0 +1,210 @@
+import React, { type ComponentProps, useEffect, useMemo } from 'react';
+import clsx from 'clsx';
+import {
+  ThemeClassNames,
+  useThemeConfig,
+  usePrevious,
+  Collapsible,
+  useCollapsible,
+} from '@docusaurus/theme-common';
+import {
+  isActiveSidebarItem,
+  findFirstCategoryLink,
+  useDocSidebarItemsExpandedState,
+  isSamePath,
+} from '@docusaurus/theme-common/internal';
+import Link from '@docusaurus/Link';
+import { translate } from '@docusaurus/Translate';
+import useIsBrowser from '@docusaurus/useIsBrowser';
+import DocSidebarItems from '@theme/DocSidebarItems';
+import type { Props } from '@theme/DocSidebarItem/Category';
+import { useHistory } from '@docusaurus/router';
+
+// If we navigate to a category and it becomes active, it should automatically
+// expand itself
+function useAutoExpandActiveCategory({
+  isActive,
+  collapsed,
+  updateCollapsed,
+}: {
+  isActive: boolean;
+  collapsed: boolean;
+  updateCollapsed: (b: boolean) => void;
+}) {
+  const wasActive = usePrevious(isActive);
+  useEffect(() => {
+    const justBecameActive = isActive && !wasActive;
+    if (justBecameActive && collapsed) {
+      updateCollapsed(false);
+    }
+  }, [isActive, wasActive, collapsed, updateCollapsed]);
+}
+
+/**
+ * When a collapsible category has no link, we still link it to its first child
+ * during SSR as a temporary fallback. This allows to be able to navigate inside
+ * the category even when JS fails to load, is delayed or simply disabled
+ * React hydration becomes an optional progressive enhancement
+ * see https://github.com/facebookincubator/infima/issues/36#issuecomment-772543188
+ * see https://github.com/facebook/docusaurus/issues/3030
+ */
+function useCategoryHrefWithSSRFallback(
+  item: Props['item']
+): string | undefined {
+  const isBrowser = useIsBrowser();
+  return useMemo(() => {
+    if (item.href) {
+      return item.href;
+    }
+    // In these cases, it's not necessary to render a fallback
+    // We skip the "findFirstCategoryLink" computation
+    if (isBrowser || !item.collapsible) {
+      return undefined;
+    }
+    return findFirstCategoryLink(item);
+  }, [item, isBrowser]);
+}
+
+function CollapseButton({
+  categoryLabel,
+  onClick,
+}: {
+  categoryLabel: string;
+  onClick: ComponentProps<'button'>['onClick'];
+}) {
+  return (
+    <button
+      aria-label={translate(
+        {
+          id: 'theme.DocSidebarItem.toggleCollapsedCategoryAriaLabel',
+          message: "Toggle the collapsible sidebar category '{label}'",
+          description:
+            'The ARIA label to toggle the collapsible sidebar category',
+        },
+        { label: categoryLabel }
+      )}
+      type="button"
+      className="clean-btn menu__caret"
+      onClick={onClick}
+    />
+  );
+}
+
+export default function DocSidebarItemCategory({
+  item,
+  onItemClick,
+  activePath,
+  level,
+  index,
+  ...props
+}: Props): JSX.Element {
+  const { items, label, collapsible, className, href } = item;
+  const {
+    docs: {
+      sidebar: { autoCollapseCategories },
+    },
+  } = useThemeConfig();
+  const hrefWithSSRFallback = useCategoryHrefWithSSRFallback(item);
+
+  const isActive = isActiveSidebarItem(item, activePath);
+  const isCurrentPage = isSamePath(href, activePath);
+  const history = useHistory();
+
+  const { collapsed, setCollapsed } = useCollapsible({
+    // Active categories are always initialized as expanded. The default
+    // (`item.collapsed`) is only used for non-active categories.
+    initialState: () => {
+      if (!collapsible) {
+        return false;
+      }
+      return isActive ? false : item.collapsed;
+    },
+  });
+
+  const { expandedItem, setExpandedItem } = useDocSidebarItemsExpandedState();
+  // Use this instead of `setCollapsed`, because it is also reactive
+  const updateCollapsed = (toCollapsed: boolean = !collapsed) => {
+    setExpandedItem(toCollapsed ? null : index);
+    setCollapsed(toCollapsed);
+  };
+  useAutoExpandActiveCategory({ isActive, collapsed, updateCollapsed });
+  useEffect(() => {
+    if (
+      collapsible &&
+      expandedItem != null &&
+      expandedItem !== index &&
+      autoCollapseCategories
+    ) {
+      setCollapsed(true);
+    }
+  }, [collapsible, expandedItem, index, setCollapsed, autoCollapseCategories]);
+
+  return (
+    <li
+      className={clsx(
+        ThemeClassNames.docs.docSidebarItemCategory,
+        ThemeClassNames.docs.docSidebarItemCategoryLevel(level),
+        'menu__list-item',
+        {
+          'menu__list-item--collapsed': collapsed,
+        },
+        className
+      )}
+    >
+      <div
+        className={clsx('menu__list-item-collapsible', {
+          'menu__list-item-collapsible--active': isCurrentPage,
+        })}
+      >
+        <Link
+          className={clsx('menu__link', {
+            'menu__link--sublist': collapsible,
+            'menu__link--sublist-caret': !href && collapsible,
+            'menu__link--active': isActive,
+          })}
+          onClick={
+            collapsible
+              ? (e) => {
+                  onItemClick?.(item);
+                  if (href) {
+                    updateCollapsed(false);
+                  } else {
+                    e.preventDefault();
+                    updateCollapsed();
+                  }
+                }
+              : () => {
+                  onItemClick?.(item);
+                }
+          }
+          aria-current={isCurrentPage ? 'page' : undefined}
+          aria-expanded={collapsible ? !collapsed : undefined}
+          href={collapsible ? hrefWithSSRFallback ?? '#' : hrefWithSSRFallback}
+          {...props}
+        >
+          {label}
+        </Link>
+        {href && collapsible && (
+          <CollapseButton
+            categoryLabel={label}
+            onClick={(e) => {
+              e.preventDefault();
+              updateCollapsed();
+              collapsed && history.push(hrefWithSSRFallback);
+            }}
+          />
+        )}
+      </div>
+
+      <Collapsible lazy as="ul" className="menu__list" collapsed={collapsed}>
+        <DocSidebarItems
+          items={items}
+          tabIndex={collapsed ? -1 : 0}
+          onItemClick={onItemClick}
+          activePath={activePath}
+          level={level + 1}
+        />
+      </Collapsible>
+    </li>
+  );
+}