Is ``class A extends (B<T>)<T> {}`` valid code?

[fisker]

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Comment

Currently, there is no syntax error for

class A extends (B<T>)<T> {}

https://www.typescriptlang.org/play/?#code/MYGwhgzhAECC0FMAeAXBA7AJjAFAIQB4AVAPgEpiToBvAXyA

Context: typescript-eslint/typescript-eslint#12012

[fisker]

Not sure if I should open a separate issue, but are the following two cases equivalent?

class A extends (B<T>) {}

class A extends B<T> {}

It's also about the typescript-eslint issue typescript-eslint/typescript-eslint#12012

[mkantor]

there is no syntax error

I see multiple errors in the playground you linked to:

Some can be eliminated by defining B and T, but others remain.

[mkantor]

are the following two cases equivalent?

class A extends (B<T>) {}

class A extends B<T> {}

They aren't.

I'm not certain this is correct, but I believe the parentheses introduce a new type parameter scope where no T is defined (note that class A<T> extends (B<string>) {} is legal). EDIT: Actually, with the parentheses it's probably parsed as an instantiation expression.

[fisker]

I see multiple errors

I mean, the playground didn't refuse to parse.

[fisker]

note that class A extends (B) {} is legal

So, are they equivalent? 😄

class A1<T> extends (B<string>) {}
class A2<T> extends B<string> {}

[RyanCavanaugh]

I don't understand the question in the context of the linked thread

Maybe this can be made to be an explicit semantic error in TS so we can then make it a parser error?

It's already a semantic error. What are you asking for?