Add LiteralList and JoinUnion types

[benzaria]

Closes #904

Added:

• LiteralList a validator to check if a Tuple have exactly one of each member in given Union, No duplicate, Extras, or Less elements.
• JoinUnion join a union members with the given delimiter (default: ',').

Example:

type Union = 'a' | 'b' | 'c' | 'd';

declare function func<const T extends unknown[]>(x: LiteralList<T, Union>): typeof x;
const bar1 = ['b', 'd', 'a', 'c'] as const
const bar2 = ['a', 'b', 'c', 'c'] as const
const bar3 = ['a', 'b', 'c'] as const

func(bar1); // Fine
func(bar2); // Error: Type ['a', 'b', 'c', 'c'] is missing Properties: ['d']
func(bar3); // Error: Type ['a', 'b', 'c'] is not the required Length of: 4

Errors example

[som-sm]

This PR doesn't look like it's ready.

Also, this needs further discussion about whether we want to do a type that returns error strings. And, this doesn't really close #904.

[benzaria]

This PR doesn't look like it's ready.

Also, this needs further discussion about whether we want to do a type that returns error strings. And, this doesn't really close #904.

ur right this is a weird scenario to return strings as Errors, like they are not needed actually but they can add a visual reason why the type is erroring. we can remove them in case @sindresorhus refuses.

and lets be honest making the type #904 as suggested is not wort the effort for 4/5 union members

[benzaria]

@sindresorhus Can u give a thought on returning the string Errors so we can go forward.

[sindresorhus]

I agree that returning Error is kinda weird, but since there is no other way to report errors to the users, I'm kinda willing to do it, because some weird Error is better than no indication of what's wrong.

I assume this solution does not suffer from performance issues like the one proposed in #904?

[som-sm]

Here's a quick demo of how it looks with a custom error string vs never.

Custom Error String Example

never Example

Surely feels better with the custom error string, just that we'd have to ensure the error string is built properly.

[benzaria]

@som-sm @sindresorhus I improved the errors! I think they look good and match with ts errors look

[benzaria]

@som-sm PR is ready, can u review !

[sindresorhus]

Please run everything through AI, as requested multiple times on other pull requests (please do it on all your pull requests).

[benzaria]

@sindresorhus Fixed Capitalized words in Error phrases

[benzaria]

@som-sm Approved !

[som-sm]

Yeah, I'm aware. I'll get to this sometime this week.

[benzaria]

@som-sm, Hey 👋 just following up on this, you mentioned you’d review it next week, but I haven’t seen any updates yet.
No rush if you’re busy, I just wanted to check whether there’s anything else needed from my side to move this forward.

[benzaria]

@som-sm Could you please take some time to review this PR when you get a chance, so we can move it forward?