fix: preserve capitalization after heading prefixes

src/index.ts

@@ -9,6 +9,7 @@ const AST_FORMAT = 'heading-case-mdast';
 
 type MarkdownNode = {
   children?: MarkdownNode[];
+  referenceType?: string;
   type?: string;
   value?: string;
 };
@@ -29,7 +30,20 @@ const collectWordNodes = (node: MarkdownNode, words: MarkdownNode[]) => {
 
 const formatHeading = (heading: MarkdownNode) => {
   const wordNodes: MarkdownNode[] = [];
-  collectWordNodes(heading, wordNodes);
+  const children = heading.children ?? [];
+
+  // A leading `[Label]` can be parsed as a shortcut link reference when the
+  // document contains a matching reference definition. Treat it as a heading
+  // prefix either way, so the word after it remains the first English word.
+  const contentNodes =
+    children[0]?.type === 'linkReference' &&
+    children[0].referenceType === 'shortcut'
+      ? children.slice(1)
+      : children;
+
+  for (const child of contentNodes) {
+    collectWordNodes(child, wordNodes);
+  }
 
   const words: WordMeta[] = wordNodes.map((node) => ({
     type: node.type === 'whitespace' ? 'space' : 'word',

test/index.test.js

@@ -36,6 +36,12 @@ test('should format line as expected', () => {
   // Number
   assert.deepStrictEqual(formatLine('# 1. Hello World'), '# 1. Hello world');
 
+  // Prefix
+  assert.deepStrictEqual(
+    formatLine('## [Important] Package name'),
+    '## [Important] Package name',
+  );
+
   // Chinese
   assert.deepStrictEqual(
     formatLine('# 你好 Hello World'),

test/prettier.test.js

@@ -13,6 +13,8 @@ test('should format Markdown and MDX headings with Prettier', async () => {
     '',
     '# Hello **Bold World** and React Router',
     '',
+    '## [Important] Package name',
+    '',
     'Setext Heading',
     '==============',
     '',
@@ -29,6 +31,8 @@ test('should format Markdown and MDX headings with Prettier', async () => {
     '',
     '# Hello **bold world** and React Router',
     '',
+    '## [Important] Package name',
+    '',
     'Setext heading',
     '==============',
     '',
@@ -67,6 +71,30 @@ test('should format Markdown and MDX headings with Prettier', async () => {
   );
 });
 
+test('should preserve the first word after a bracketed heading prefix', async () => {
+  const markdown = [
+    '## [Important] Package Name',
+    '',
+    '[Important]: https://example.com',
+    '',
+  ].join('\n');
+
+  const expected = [
+    '## [Important] Package name',
+    '',
+    '[Important]: https://example.com',
+    '',
+  ].join('\n');
+
+  assert.strictEqual(
+    await prettier.format(markdown, {
+      parser: 'markdown',
+      plugins: [plugin],
+    }),
+    expected,
+  );
+});
+
 test('should load the package entry as a Prettier plugin through rs fmt', async () => {
   const projectRoot = path.resolve(import.meta.dirname, '..');
   const cwd = await fs.mkdtemp(path.join(projectRoot, '.heading-case-rs-fmt-'));