feat(mdx-loader): Remark plugin to report unused MDX / Markdown directives (#9394)

Co-authored-by: sebastienlorber <lorber.sebastien@gmail.com>

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

@@ -15,8 +15,10 @@ import details from './remark/details';
 import head from './remark/head';
 import mermaid from './remark/mermaid';
 import transformAdmonitions from './remark/admonitions';
+import unusedDirectivesWarning from './remark/unusedDirectives';
 import codeCompatPlugin from './remark/mdx1Compat/codeCompatPlugin';
 import {getFormat} from './format';
+import type {WebpackCompilerName} from '@docusaurus/utils';
 import type {MDXFrontMatter} from './frontMatter';
 import type {Options} from './loader';
 import type {AdmonitionOptions} from './remark/admonitions';
@@ -37,10 +39,12 @@ type SimpleProcessor = {
     content,
     filePath,
     frontMatter,
+    compilerName,
   }: {
     content: string;
     filePath: string;
     frontMatter: {[key: string]: unknown};
+    compilerName: WebpackCompilerName;
   }) => Promise<SimpleProcessorResult>;
 };
 
@@ -123,6 +127,7 @@ async function createProcessorFactory() {
       gfm,
       options.markdownConfig.mdx1Compat.comments ? comment : null,
       ...(options.remarkPlugins ?? []),
+      unusedDirectivesWarning,
     ].filter((plugin): plugin is MDXPlugin => Boolean(plugin));
 
     // codeCompatPlugin needs to be applied last after user-provided plugins
@@ -167,12 +172,13 @@ async function createProcessorFactory() {
     });
 
     return {
-      process: async ({content, filePath, frontMatter}) => {
+      process: async ({content, filePath, frontMatter, compilerName}) => {
         const vfile = new VFile({
           value: content,
           path: filePath,
           data: {
             frontMatter,
+            compilerName,
           },
         });
         return mdxProcessor.process(vfile).then((result) => ({