feat(v2): allow specifying TOC max depth (themeConfig + frontMatter) (#5578)

* feat: add all TOC levels to MDX loader

* feat: add theme-level config for heading depth

* test: add remark MDX loader test

* fix: limit maxDepth validation to H2 - H6

* refactor: set default `maxDepth` using `joi`

* refactor: `maxDepth` -> `maxHeadingLevel

* refactor: invert underlying TOC depth API

* refactor: make TOC algorithm level-aware

* feat: add support for per-doc TOC heading levels

* feat: support document-level heading levels for blog

* fix: correct validation for toc level frontmatter

* fix: ensure TOC doesn't generate redundant DOM

* perf: simpler TOC heading search alg

* docs: document heading level props for `TOCInline`

* Update website/docs/guides/markdown-features/markdown-features-inline-toc.mdx

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>

* docs: fix docs (again)

* create dedicated  test file for heading searching logic: exhaustive tests will be simpler to write

* toc search: add real-world test

* fix test

* add dogfooding tests for toc min/max

* add test for min/max toc frontmatter

* reverse min/max order

* add theme minHeadingLevel + tests

* simpler TOC rendering logic

* simplify TOC implementation (temp, WIP)

* reverse unnatural order for minHeadingLevel/maxHeadingLevel

* add TOC dogfooding tests to all content plugins

* expose toc min/max heading level frontmatter to all 3 content plugins

* refactor blogLayout: accept toc ReactElement directly

* move toc utils to theme-common

* add tests for filterTOC

* create new generic TOCItems component

* useless css file copied

* fix toc highlighting className conflicts

* update doc

* fix types

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>
Co-authored-by: slorber <lorber.sebastien@gmail.com>

packages/docusaurus-theme-classic/src/theme/TOCItems/index.tsx

@@ -0,0 +1,96 @@
+/**
+ * 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 React, {useMemo} from 'react';
+import type {TOCItemsProps} from '@theme/TOCItems';
+import {TOCItem} from '@docusaurus/types';
+import {
+  TOCHighlightConfig,
+  useThemeConfig,
+  useTOCFilter,
+  useTOCHighlight,
+} from '@docusaurus/theme-common';
+
+// Recursive component rendering the toc tree
+/* eslint-disable jsx-a11y/control-has-associated-label */
+function TOCItemList({
+  toc,
+  className = 'table-of-contents table-of-contents__left-border',
+  linkClassName = 'table-of-contents__link',
+  isChild,
+}: {
+  readonly toc: readonly TOCItem[];
+  readonly className: string;
+  readonly linkClassName: string;
+  readonly isChild?: boolean;
+}): JSX.Element | null {
+  if (!toc.length) {
+    return null;
+  }
+  return (
+    <ul className={isChild ? '' : className}>
+      {toc.map((heading) => (
+        <li key={heading.id}>
+          <a
+            href={`#${heading.id}`}
+            className={linkClassName}
+            // Developer provided the HTML, so assume it's safe.
+            // eslint-disable-next-line react/no-danger
+            dangerouslySetInnerHTML={{__html: heading.value}}
+          />
+          <TOCItemList
+            isChild
+            toc={heading.children}
+            className={className}
+            linkClassName={linkClassName}
+          />
+        </li>
+      ))}
+    </ul>
+  );
+}
+
+export default function TOCItems({
+  toc,
+  className = 'table-of-contents table-of-contents__left-border',
+  linkClassName = 'table-of-contents__link',
+  linkActiveClassName = undefined,
+  minHeadingLevel: minHeadingLevelOption,
+  maxHeadingLevel: maxHeadingLevelOption,
+  ...props
+}: TOCItemsProps): JSX.Element | null {
+  const themeConfig = useThemeConfig();
+
+  const minHeadingLevel =
+    minHeadingLevelOption ?? themeConfig.tableOfContents.minHeadingLevel;
+  const maxHeadingLevel =
+    maxHeadingLevelOption ?? themeConfig.tableOfContents.maxHeadingLevel;
+
+  const tocFiltered = useTOCFilter({toc, minHeadingLevel, maxHeadingLevel});
+
+  const tocHighlightConfig: TOCHighlightConfig | undefined = useMemo(() => {
+    if (linkClassName && linkActiveClassName) {
+      return {
+        linkClassName,
+        linkActiveClassName,
+        minHeadingLevel,
+        maxHeadingLevel,
+      };
+    }
+    return undefined;
+  }, [linkClassName, linkActiveClassName, minHeadingLevel, maxHeadingLevel]);
+  useTOCHighlight(tocHighlightConfig);
+
+  return (
+    <TOCItemList
+      toc={tocFiltered}
+      className={className}
+      linkClassName={linkClassName}
+      {...props}
+    />
+  );
+}