Regression: Allow specifying empty object in Data.TaggedEnum about effect HOT 5 CLOSED

You should not use Record<string, never> in a tagged enum declaration, as that is not equivalent to {} (an object with no keys).

from effect.

The ESLint rules enabled by plugin:@typescript-eslint/recommended includes the ban-types rule, and this specifically bans {}. I'm no expert in TypeScript internals, so I'll defer to existing discussions.

This comment explains their logic behind banning {}: typescript-eslint/typescript-eslint#2063 (comment)

There is additional discussion here: microsoft/TypeScript#47486.

If Record<string, never> is indeed correct, then we can certainly ignore the rule when using taggedEnum.

from effect.

If you have to use Record, then the correct type would be Record<never, never>.

from effect.

I tested that as well, and it seems Record<never, never> is equivalent to {}. It allows any non-nullish value.

// allows any key (does not enforce empty object)
const objectTest: Record<never, never> = { x: 1 }
// allows non-object values
const stringTest: Record<never, never> = "hello"
const boolTest: Record<never, never> = true
const numberTest: Record<never, never> = 1
const arrayTest: Record<never, never> = [1, 2, 3]
// this fails - `null` is not allowed
const fails: Record<never, never> = null

from effect.

While general usage of the type {} may be discouraged in this case it is really not an issue, at the end the type you'll work with is { _tag: yourTag } so this is rather an issue with a too strict eslint rule, as Tim suggested if you want to keep such rule you can use Record<never, never>

from effect.