`configs` field is wrongly optional in the type definition

[rhysd]

Repro

Run tsc on this eslint.config.mjs.

import ts from 'typescript-eslint';
import mocha from 'eslint-plugin-mocha';

export default ts.config(
    mocha.configs['recommended'],
);

Expected behavior

Type check should pass.

Actual behavior

Got the following errors.

eslint.config.mjs:10:5 - error TS18048: 'mocha.configs' is possibly 'undefined'.

10     mocha.configs['recommended'],
       ~~~~~~~~~~~~~

eslint.config.mjs:10:5 - error TS2345: Argument of type 'LegacyConfig<RulesRecord, RulesRecord> | Config<RulesRecord> | Config<RulesRecord>[]' is not assignable to parameter of type 'InfiniteDepthConfigWithExtends'.
  Type 'LegacyConfig<RulesRecord, RulesRecord>' is not assignable to type 'InfiniteDepthConfigWithExtends'.
    Type 'LegacyConfig<RulesRecord, RulesRecord>' is not assignable to type 'ConfigWithExtends'.
      Types of property 'extends' are incompatible.
        Type 'string | string[] | undefined' is not assignable to type 'InfiniteDepthConfigWithExtends[] | undefined'.
          Type 'string' is not assignable to type 'InfiniteDepthConfigWithExtends[]'.

10     mocha.configs['recommended'],
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 2 errors in the same file, starting at: eslint.config.mjs:10

Description

These errors were caused because the mocha instance is typed as ESLint.Plugin.

eslint-plugin-mocha/source/plugin.ts

Line 81 in 1e5a3a1

const mochaPlugin: ESLint.Plugin = {

ESLint.Plugin is a generic eslint plugin object which knows nothing about eslint-plugin-mocha. So it types configs field as optional. However eslint-plugin-mocha actually sets the configs field and the field should not be optional.