Type constrain will cause the inferred type to be less specific

[weichensw]

TypeScript Version: 3.2.0-dev.20181107

Search Terms:
Type constrain inferred
Code

function test1<P extends any[], R>(
  t: ((...args: P) => R),
): (...args: P) => R {
    return t;
}

function wrap1<T extends (...args: any[]) => any>(resultFn: T): T{
    return resultFn;
}

const test11 = wrap1(test1);

function wrap2<T>(resultFn: T): T{
    return resultFn;
}

const test12 = wrap2(test1);

Expected behavior:
typeof test11 should be the same as typeof test1 as the wrap1 function takes T and return T.
Actual behavior:
typeof test11 is more generic than typeof test1. Meanwhile, wrap2 works as intended, except it doesn't have type constrain.

Playground Link:
Playground Link

Related Issues:
N/A

[RyanCavanaugh]

Either this is a bug or the logic for moving type parameters to the return type intentionally considers the constraint to be a request from the signature to effectively instantiate the generic function. Not sure which.

[ahejlsberg]

Fixed by #33228.