TypeError: Cannot redefine plugin

[zwaittt]

happens when migrate legacy eslintrc config with flat configs.

const { FlatCompat } = require("@eslint/eslintrc");
const antfu = require('@antfu/eslint-config').default;

const compat = new FlatCompat({});

module.exports = [
  ...compat.config({
    "extends": "next/core-web-vitals"
  }),
  ...antfu({
    typescript: true,
  }),
];

Oops! Something went wrong! :(

ESLint: 8.53.0

TypeError: Cannot redefine plugin "import".

both legacy and flat from @antfu/eslint-config contains eslint-plugin-import, but seems this was fixed in #91

[nzakas]

If it seems it was fixed, then what is this issue reporting?

[zwaittt]

My bad, I mean maybe the issue related in #91 is't fixed actually. The following stackblitz project shows the error I encountered.
https://stackblitz.com/edit/stackblitz-starters-79aqit?file=package.json

[nzakas]

Thanks, that's very helpful. I'll take a look.

[nzakas]

Okay, so there is an issue here. As part of loading configuration information, we normalize the plugin:

eslintrc/lib/config-array-factory.js

Lines 410 to 430 in af564ff

	function normalizePlugin(plugin) {
	// first check the cache
	let normalizedPlugin = normalizedPlugins.get(plugin);
	if (normalizedPlugin) {
	return normalizedPlugin;
	}
	normalizedPlugin = {
	configs: plugin.configs || {},
	environments: plugin.environments || {},
	processors: plugin.processors || {},
	rules: plugin.rules || {}
	};
	// save the reference for later
	normalizedPlugins.set(plugin, normalizedPlugin);
	return normalizedPlugin;
	}

This is actually problematic for a couple of reasons:

1. We lose the original plugin reference
2. We lose any meta information that might be on the object.

I know the intent of this normalization was to prevent us from needing to check if a plugin had properly defined configs, rules, etc.

I see two potential solutions to this:

1. Stop normalizing plugins. It appears that the only place that uses this information is config-array.js, so I think we can make this change without affecting ESLint as a whole.
2. Normalize smarter. We could normalize in a way that retains the original plugin reference, perhaps by using Object.create() on the plugin first. This would also require a corresponding change in ESLint to check for the prototype (or wherever we store the original plugin reference).

I'd appreciate some thoughts from @eslint/eslint-team on this.

[mdjermanovic]

Maybe we could add new property ConfigDependency#originalDefinition (the original plugin reference) and use it in FlatCompat instead of the normalized definition.

eslintrc/lib/flat-compat.js

Line 135 in af564ff

const { definition: plugin, error } = eslintrcConfig.plugins[pluginName];

I think that would be the change with the least chance of breaking something.

I just tried it and the stackblitz example seems to be working well after the change.

[nzakas]

Ah, that's a great idea variation of option 2. I'll put together a PR.

[matthew-dean]

This issue is driving me crazy. I'm migrating to the flat config file format, and I have lots of errors like:

Cannot redefine plugin "vue"
...
Cannot redefine plugin "storybook"

I think the issue is that sub-configs, such as @nuxt/eslint-config use plugins like eslint-plugin-vue, with a different version. However, IMO that should be perfectly valid, especially when the "final" configuration for me .vue files is applying @nuxt/eslint-config.

This is an issue that's brand new to the eslint flat config and is not fixed yet. Please re-open.

[matthew-dean]

Note that I've run pnpm why eslint-plugin-storybook -r and there's only one version of this plugin installed.

Hmm, it seems that's because my root eslint.config.js has:

  ...compat.config({
    overrides: [
      {
        extends: ['standard', 'plugin:storybook/recommended'],
        files: ['*.js']
      }
    ]
  }),

And a package eslint.config.js has:

  ...compat.extends(
    '@nuxt/eslint-config',
    'plugin:storybook/recommended'
  ),

Removing the root fixes it, but regardless:

1. This was not previously a problem.
2. There's still only one plugin being referenced, but ESLint still gets confused.