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Link to the rule's documentation

https://typescript-eslint.io/rules/no-unnecessary-type-parameters

Description

Splitting out of #9536 (comment) -> #9529 (comment), there are two usability improvements we'd like for @typescript-eslint/no-unnecessary-type-parameters:

• Enhancement: [no-unnecessary-type-parameters] Special case tuples and parameter arrays as a "single use" generic type #9529 itself: changing the default behavior of the rule
• This issue, separately: adding an opt-in option to mark some more types as "single-use"

For context, the rule right now is surprisingly limited in functionality because of types like arrays actually having multiple uses of their type parameters: https://typescript-eslint.io/rules/no-unnecessary-type-parameters/#limitations. Being able to mark known safe types as "single-use" would let people opt into a stricter form of the rule.

Fail

/* @typescript-eslint/no-unnecessary-type-parameters: "error", { "allow": [{ "from": "lib", "name": "Array" }] */
class ClassyArray<T> {
  arr: T[];
}

Pass

/* @typescript-eslint/no-unnecessary-type-parameters: "error" */
class ClassyArray<T> {
  arr: T[];
}

Additional Info

I think we'd want to special-case the report message for the rule in these cases. If someone is using it configured to ignore arrays, then is surprised that it complains on a construct using arrays, they should know it's from their custom config - not faulty rule logic.

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