refactor: mark toc in loaded MDX as non-optional (#7524)

packages/docusaurus-mdx-loader/src/index.ts

@@ -21,7 +21,7 @@ export type LoadedMDXContent<FrontMatter, Metadata, Assets = undefined> = {
   /** As provided by the content plugin. */
   readonly metadata: Metadata;
   /** A list of TOC items (headings). */
-  readonly toc?: readonly TOCItem[];
+  readonly toc: readonly TOCItem[];
   /** First h1 title before any content. */
   readonly contentTitle: string | undefined;
   /**

packages/docusaurus-mdx-loader/src/remark/toc/__tests__/__fixtures__/no-heading.md

@@ -0,0 +1,7 @@
+foo
+
+`bar`
+
+```js
+baz
+```

packages/docusaurus-mdx-loader/src/remark/toc/__tests__/__snapshots__/index.test.ts.snap

@@ -119,6 +119,19 @@ Content.
 "
 `;
 
+exports[`toc remark plugin outputs empty array for no TOC 1`] = `
+"export const toc = [];
+
+foo
+
+\`bar\`
+
+\`\`\`js
+baz
+\`\`\`
+"
+`;
+
 exports[`toc remark plugin works on non text phrasing content 1`] = `
 "export const toc = [
 	{

packages/docusaurus-mdx-loader/src/remark/toc/__tests__/index.test.ts

@@ -25,6 +25,11 @@ const processFixture = async (name: string) => {
 };
 
 describe('toc remark plugin', () => {
+  it('outputs empty array for no TOC', async () => {
+    const result = await processFixture('no-heading');
+    expect(result).toMatchSnapshot();
+  });
+
   it('works on non text phrasing content', async () => {
     const result = await processFixture('non-text-content');
     expect(result).toMatchSnapshot();

packages/docusaurus-mdx-loader/src/remark/toc/index.ts

@@ -89,10 +89,8 @@ export default function plugin(): Transformer {
     const {children} = root as Parent<Literal>;
     const targetIndex = getOrCreateExistingTargetIndex(children);
 
-    if (headings.length) {
-      children[targetIndex]!.value = `export const ${name} = ${stringifyObject(
-        headings,
-      )};`;
-    }
+    children[targetIndex]!.value = `export const ${name} = ${stringifyObject(
+      headings,
+    )};`;
   };
 }