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While I definitely like the idea of this, ultimately this doesn't actually do anything.

The type of Token['value'] is string.
Because TypeScript doesn't support exclusions from the primitive types - Excludes<string, '=>'> just results in string.

Exclude<TSESTree.Token, TSESTree.Comment> OTOH does do something as Comment is a distinct type in the union, which can be excluded.

@bradzacher You think there's another way of getting the correct type then?

Edit: posted https://twitter.com/MichaelDeBoey93/status/1401920255404953604 to get some help

There is unfortunately not right now.
There was a TS issue about "negative" types a while back. It's something the TS team has thought about but has not implemented.

Edit: orta dug up the issue: microsoft/TypeScript#29317

@bradzacher microsoft/TypeScript#29317 is the issue as mentioned by @orta in https://twitter.com/orta/status/1401934733634846723

So there's no other way to do this then?
Not even when it's a complicated way?

@bradzacher Making the value of PunctuatorToken equal to '=>' | '}' | ']' | ')' | ':' | ',' | '{' | '[' | ... for instance? 🤔

interface PunctuatorToken extends BaseToken {
  type: AST_TOKEN_TYPES.Punctuator;
  value: '=>' | '}' | ']' | ')' | ':' | ',' | '{' | '[' | ...;
}

Correct, but then we would have to attempt to list out every single possible token string and keep it up to date.

Not an impossible task, just a (relatively) low value one.

Also it's not a great thing because custom parsers (babel, Vue, markdown, angular) may add new tokens, which then causes our types to be wrong. By-and-large our rules shouldn't make assumptions about the parser.

@bradzacher This PR adds type-safety and type guards for those functions.
I know I'm biased, but I think the "low value maintenance" of the value type is subordinate to the extra value you get from having the type guards I think?

What do you think?
Should we proceed here?

I'm happy to create another PR to update the value type if that's preferred btw.

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@bradzacher Now that #3496 is merged, this one can be merged too I think?