`noImplicitAny` and generic arrow functions misbehave

[zerkms]

TypeScript Version: playground (2.1.4-insiders.20161201)

Code

The following code should be run with the noImplicitAny set:

let f1: <T>(a: T) => T = a => a;

function f2<T>(a: T): T {
    return a;
};

Expected behavior:

Both functions should compile fine.

Actual behavior:

The f1 arrow function fails the type check as the compiler thinks a is of any type.

[mhegazy]

When the compiler compares any generic signature, it erases the generic type parameters, and replaces them with any. the result is that the parameter on the right hand-side here gets a type any implicitly. the error is telling you that this has happened.

If the compiler gets "smarter" comparing generic signatures, the error would go away.

[zpdDG4gta8XKpMCd]

If the compiler gets "smarter" comparing generic signatures, the error would go away.

what are the chances?

[zerkms]

@mhegazy what is the final resolution?

[mhegazy]

@mhegazy what is the final resolution?

resolutions, just like types, are always open in TS :D

Should be tracked under #9366