Class expressions don't support constructors that return any

[spion]

Example:

function f(T:{new (...args:any[]):any}) {
    return class extends T {}
}

Error:

src/test.ts(2,23): error TS2509: Base constructor return type 'any' is not a class or interface type.

Seemingly arbitrary fix:

interface I {}
function f(T:{new (...args:any[]):I}) {
    return class extends T {}
}

Afaik any should be an acceptable type here?

[mhegazy]

Extend clause only supports object types, no type arguments, no intersection, no union, and since any can be any of these, it is not supported. a target of an extend clause must be something that has a "known shape", so that the extend checks can run when checking the class body, and give meaningful errors about what a class did or did not extend incorrectly.

i think this issue is a duplicate of #4890

[spion]

There is a meaningful way to check whether it extends {}. That doesn't work either though:

function f(T:{new (...args:any[]):{}}) {
    return class extends T {}
}

Yields the same error.

If however you use a named interface, it doesn't. I can maybe accept any not unifying with something (not really, it doesn't make sense, but lets say it does as there is no structure to check), but rejecting an interface just because its anonymous, not defined as an interface { ... } - that part seems way too arbitrary to me.