flat config does not work as documented

[danielrentz]

When using config "flat/recommended-with-json" (eslint.config.js) in an environment linting *.js and *.json together, the plugin fails:

TypeError: Key "rules": Key "jsonc/comma-dangle": Could not find plugin "jsonc".

Root cause seems that the config contains two objects. The first one correctly configures the plugin. However, the second object contains the recommended rules without a "files" property, thus ESLint tries to apply these rules on all JS files.

My current workaround is:

return [
  // ...
  eslintPluginJson.configs["flat/recommended-with-json"][0],

  {
    files: ["**/*.json"],
    rules: {
      ...eslintPluginJson.configs["flat/recommended-with-json"][1].rules,
      // ... extra rules
    },
  }
];

See also ota-meshi/eslint-plugin-yml#310