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

The following is neither a type nor runtime error:

tseslint.config({
  extends: [
    {
      extends: [
        {
          rules: {
            rule1: "error",
          },
        },
      ],
    },
  ],
})

and it results in

[
  {
    extends: [
      {
        rules: {
          rule1: "error",
        },
      },
    ],
  },
]

This means that

tseslint.config(
  tseslint.config({
    extends: [
      {
        extends: [
          {
            rules: {
              rule1: "error",
            },
          },
        ],
      },
    ],
  }),
)

results in

[
  {
    rules: {
      rule1: "error",
    },
  },
]

and, therefore tseslint.config() is not idempotent. I think we want to avoid this behavior, especially since it means that defineConfig(tseslint.config()), which is now being promoted against our recommendation, will be similarly problematic.

Additional Info

Note that eslint core defineConfig() does explicitly error on this case: https://github.com/eslint/rewrite/blob/0496201974aad87fdcf3aa2a63ec74e91b54825e/packages/config-helpers/src/define-config.js#L452-L454