Support Frontmatter

[muuvmuuv]

Subject of the feature

I'm currently creating a new eslint setup in my project and everything seems fine but when I lint .mdx files I'm getting the below warning. I couldn't find anything in the docs or if it is even already supported but frontmatter support is necessary.

.../src/pages/about.mdx
  1:3  error  Parsing error: Invalid left-hand side in prefix operation

> 1 | ---
    |   ^
  2 | title: 'About Me'
  3 | ---
  4 |

Problem

No frontmatter support

Expected behavior

Should ignore the frontmatter section or lint it if it is possible (indention etc.)

Alternatives

What are the alternative solutions? Please describe what else you have considered?

Additional information

My eslint config:

{
  "parser": "babel-eslint",
  "plugins": [
    "import"
  ],
  "extends": [
    "eslint:recommended",
    "plugin:import/errors",
    "plugin:import/warnings",
    "plugin:react/recommended",
    "plugin:mdx/recommended",
    "plugin:jsx-a11y/strict",
    "plugin:prettier/recommended"
  ],
  "env": {
    "es6": true,
    "browser": true,
    "commonjs": true,
    "serviceworker": true
  },
  "parserOptions": {
    "sourceType": "module",
    "ecmaVersion": 2020
  },
  "settings": {
    "react": {
      "version": "detect"
    },
    "import/resolver": {
      "node": {
        "extensions": [
          ".js",
          ".jsx"
        ]
      }
    }
  },
  "rules": {
    "react/display-name": "off",
    "react/prop-types": "off",
    "import/order": [
      "error",
      {
        "groups": [
          [
            "builtin",
            "external",
            "internal"
          ]
        ]
      }
    ],
    "default-case": "off"
  }

[JounQin]

Try to use overrides of ESLint first.

First option:

{
  "parser": "babel-eslint",
  "extends": [],
  "overrides": {
    "files": "*.mdx",
    "extends": "plugin:mdx/recommended"
  }
}

Another option:

{
  "extends": ["other configs", "plugin:mdx/recommended"],
  "parserOptions": {
    "parser": "babel-eslint" // This is actually redundant, `eslint-mdx` parser will try it automatically
  }
}

The parser for .mdx files should be eslint-mdx.

And, a minimal runnable reproduction is required.

[kate-hall]

I'm also having this issue. I think there are flaws in the code suggested by JounQin above if anyone is banging their heads on this: plugin/mdx:recommended should be plugin:mdx/recommended

Note that neither suggested solution allowed frontmatter in MDX files to pass through the linter successfully.

[JounQin]

@kate-hall Hah, thanks for pointing out my typo.

Would you like to post a new issue with a minimal and runnable reproduction?