Environment

Node version: v20.5.0
npm version: v9.8.0
Local ESLint version: v8.46.0 (Currently used)
Global ESLint version: Not found
Operating System: darwin 22.5.0

What parser are you using?

Default (Espree)

What did you do?

I run eslint . with a config that contains an invalid element in the files array, e.g.:

export default [
    {
        files: [
            "**/*.js",
            undefined
        ]
    }
];

What did you expect to happen?

There should be an error message indicating that files contains an invalid value.

What actually happened?

A generic error message:

Oops! Something went wrong! :(

ESLint: 8.46.0

TypeError: Unexpected matcher type undefined.

For comparison, here is the error message printed by an eslintrc config with overrides: [{ files: ["**/*.js", undefined] }]:

Oops! Something went wrong! :(

ESLint: 8.46.0

Error: ESLint configuration in .eslintrc.js is invalid:
        - Property "overrides[0].files" is the wrong type (expected string but got `["**/*.js",null]`).
        - Property "overrides[0].files[1]" is the wrong type (expected string but got `undefined`).
        - "overrides[0].files" should match exactly one schema in oneOf. Value: ["**/*.js",null].

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-vmehy7?file=eslint.config.js&view=editor

Participation

• I am willing to submit a pull request for this issue.

Additional comments

A similar problem occurs when an ignores pattern is invalid. For example, when running eslint . with this config:

export default [
    {
        files: ["**/*.js"],
        ignores: [1],
    }
];

The error message looks like this:

Oops! Something went wrong! :(

ESLint: 8.46.0

TypeError: matcher.startsWith is not a function