Before You File a Proposal Please Confirm You Have Done The Following...

• I have searched for related issues and found none that match my proposal.
• I have searched the current rule list and found no rules that match my proposal.
• I have read the FAQ and my problem is not listed.

Relevant Package

typescript-eslint

My proposal is suitable for this project

• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Description

With ESLint v9.22 they added their own defineConfig config helper (similar to config), which does again support extends. I of course immediately tried to rewrite my ESLint config to use the new helper:

import { defineConfig, globalIgnores } from "eslint/config";
import ts from "typescript-eslint";

export default defineConfig(
    {
        plugins: {
            ts: ts.plugin
        },
        extends: [
            "ts/strict",
            "ts/stylistic",
        ],
        rules: {
            "ts/no-inferrable-types": [
                "error",
                { ignoreParameters: true, ignoreProperties: true },
            ],
        },
    },
);

Running npx eslint fails with the following error:

Oops! Something went wrong! :(

ESLint: 9.22.0

TypeError: Plugin config "ts/strict" is an eslintrc config and cannot be used in this context.
    at deepNormalizePluginConfig (C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:231:9)
    at findPluginConfig (C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:262:9)
    at C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:394:25
    at Array.map (<anonymous>)
    at processExtends (C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:392:36)
    at C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:464:38
    at Array.flatMap (<anonymous>)
    at processConfigList (C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:464:20)
    at defineConfig (C:\Users\niklaswimmer\Dev\test\node_modules\@eslint\config-helpers\dist\cjs\index.cjs:499:9)
    at file:///C:/Users/niklaswimmer/Dev/test/eslint.config.mjs?mtime=1741610408364:37:16

My understandig is that when given ts/strict ESLint tries to access ts.plugin.configs.strict, which is not the same as ts.configs.strict and not compatible with flat configs.

Additional Info

I marked this as enhancement and not as bug because the "fix" is to simply use ts.configs.strict instead of "ts/strict" (and use the full rule namespace instead of just "ts"), but I expect the current behavior to be confusing for new users (ESLint shows both options in their docs, but if one of them does not work, it will be confusing).