Lint markdown with eslint

.github/copilot-instructions.md

@@ -51,7 +51,7 @@ Always reference these instructions first and fallback to search or bash command
 
 ### Repository Structure
 
-```
+```text
 packages/
 ├── babel-plugin-display-name/     # Babel plugin for component display names
 ├── babel-plugin-minify-errors/    # Babel plugin for error minification

packages/code-infra/README.md

@@ -5,10 +5,9 @@ Scripts and configs to be used across MUI repos.
 ## Publishing packages
 
 1. Go to the publish action -
-
-- [Base UI](https://github.com/mui/base-ui/actions/workflows/publish.yml)
-- [Core](https://github.com/mui/material-ui/actions/workflows/publish.yml)
-- [MUI X](https://github.com/mui/mui-x/actions/workflows/publish.yml)
+   - [Base UI](https://github.com/mui/base-ui/actions/workflows/publish.yml)
+   - [Core](https://github.com/mui/material-ui/actions/workflows/publish.yml)
+   - [MUI X](https://github.com/mui/mui-x/actions/workflows/publish.yml)
 
 2. Choose "Run workflow" dropdown
 
@@ -22,7 +21,8 @@ Scripts and configs to be used across MUI repos.
 4. Refresh the page to see the newly created workflow, and click it.
 5. The next screen shows "@username requested your review to deploy to npm-publish", click "Review deployments" and authorize your workflow run. **Never approve workflow runs you didn't initiaite.**
 
-> [!IMPORTANT]  
+> [!IMPORTANT] <!-- eslint-disable-line markdown/no-missing-label-refs  --><!-- See https://github.com/eslint/markdown/issues/294 -->
+>
 > Go through the below steps if there is an error that says `The following packages are new and need to be published manually first` in the publish flow.
 
 ### Adding and publishing new packages
@@ -31,13 +31,13 @@ Whenever news packages are added to the repo (that will get published to npm) or
 
 1. Goto your repo's code base on your system, open terminal and run:
 
-```bash
-pnpm code-infra publish-new-package
-```
+   ```bash
+   pnpm code-infra publish-new-package
+   ```
 
-This command detects the new public packages in the repo and asks for your confirmation before publishing them to the npm registry. Add the `--dryRun` flag to skip the actual publishing.
+   This command detects the new public packages in the repo and asks for your confirmation before publishing them to the npm registry. Add the `--dryRun` flag to skip the actual publishing.
 
-2. Goto the settings link for each packages, ie, https://www.npmjs.com/package/<pkg-name>/access , and setup `Trusted Publisher`.
+2. Goto the settings link for each packages, ie, `https://www.npmjs.com/package/<pkg-name>/access` , and setup `Trusted Publisher`.
 3. In `Select your publisher` step in the above link, click on the `Github Actions` button to configure Github actions based trusted publishing.
 4. Fill in the details of the repo -
    1. `Organization or user` as `mui`,

packages/code-infra/package.json

@@ -63,6 +63,7 @@
     "@eslint/compat": "^1.4.0",
     "@eslint/js": "^9.36.0",
     "@eslint/json": "^0.13.2",
+    "@eslint/markdown": "^7.4.0",
     "@inquirer/confirm": "^5.1.19",
     "@mui/internal-babel-plugin-display-name": "workspace:*",
     "@mui/internal-babel-plugin-minify-errors": "workspace:*",
@@ -109,6 +110,7 @@
     "typescript": "^5.0.0"
   },
   "devDependencies": {
+    "@octokit/types": "^15.0.0",
     "@types/babel__core": "^7.20.5",
     "@types/babel__preset-env": "^7.10.0",
     "@types/eslint-plugin-jsx-a11y": "^6.10.0",
@@ -119,7 +121,6 @@
     "@typescript-eslint/parser": "^8.45.0",
     "@typescript-eslint/rule-tester": "^8.45.0",
     "eslint": "^9.36.0",
-    "@octokit/types": "^15.0.0",
     "prettier": "^3.6.2",
     "typescript-eslint": "^8.45.0"
   },

packages/code-infra/src/eslint/baseConfig.mjs

@@ -5,6 +5,7 @@ import prettier from 'eslint-config-prettier/flat';
 import importPlugin from 'eslint-plugin-import';
 import jsxA11yPlugin from 'eslint-plugin-jsx-a11y';
 import reactPlugin from 'eslint-plugin-react';
+import markdown from '@eslint/markdown';
 import { configs as reactCompilerPluginConfigs } from 'eslint-plugin-react-compiler';
 import reactHooks from 'eslint-plugin-react-hooks';
 import globals from 'globals';
@@ -42,6 +43,14 @@ export function createBaseConfig({
     includeIgnoreIfExists(path.join(baseDirectory, '.lintignore'), `Ignore rules from .lintignore`),
     createJsonConfig(),
     prettier,
+    // Track https://github.com/eslint/markdown/issues/316 for MDX support
+    markdown.configs.recommended,
+    {
+      files: ['**/*.md'],
+      rules: {
+        'markdown/no-duplicate-headings': 'error',
+      },
+    },
     {
       name: 'Base config',
       files: [`**/*${EXTENSION_TS}`],