fix: v3 admonitions should support v2 title syntax for nested admonitions (#9535)

Fix admonition title mdx v1 compat option when admonition is nested

packages/docusaurus-utils/src/__tests__/markdownUtils.test.ts

@@ -1288,17 +1288,23 @@ describe('admonitionTitleToDirectiveLabel', () => {
     `);
   });
 
-  it('does not transform left-padded directives', () => {
+  it('transforms space indented directives', () => {
     expect(
       admonitionTitleToDirectiveLabel(
         dedent`
         before
 
-         :::note Title
+         :::note 1 space
 
-        content
+         content
 
-        :::
+         :::
+
+          :::note 2 spaces
+
+          content
+
+          :::
 
         after
     `,
@@ -1307,16 +1313,63 @@ describe('admonitionTitleToDirectiveLabel', () => {
     ).toEqual(dedent`
         before
 
-         :::note Title
+         :::note[1 space]
 
-        content
+         content
 
-        :::
+         :::
+
+          :::note[2 spaces]
+
+          content
+
+          :::
 
         after
     `);
   });
 
+  it('transforms tab indented directives', () => {
+    expect(
+      admonitionTitleToDirectiveLabel(
+        `
+before
+
+\t:::note 1 tab
+
+\tcontent
+
+\t:::
+
+\t\t:::note 2 tabs
+
+\t\tcontent
+
+\t\t:::
+
+after
+    `,
+        directives,
+      ),
+    ).toBe(`
+before
+
+\t:::note[1 tab]
+
+\tcontent
+
+\t:::
+
+\t\t:::note[2 tabs]
+
+\t\tcontent
+
+\t\t:::
+
+after
+    `);
+  });
+
   it('does not transform admonition without title', () => {
     expect(
       admonitionTitleToDirectiveLabel(

packages/docusaurus-utils/src/markdownUtils.ts

@@ -97,14 +97,14 @@ export function admonitionTitleToDirectiveLabel(
 
   const directiveNameGroup = `(${admonitionContainerDirectives.join('|')})`;
   const regexp = new RegExp(
-    `^(?<directive>:{3,}${directiveNameGroup}) +(?<title>.*)$`,
+    `^(?<indentation>( +|\t+))?(?<directive>:{3,}${directiveNameGroup}) +(?<title>.*)$`,
     'gm',
   );
 
   return content.replaceAll(regexp, (substring, ...args: any[]) => {
     const groups = args.at(-1);
 
-    return `${groups.directive}[${groups.title}]`;
+    return `${groups.indentation ?? ''}${groups.directive}[${groups.title}]`;
   });
 }