Generic function parameters seem to ignore typecheck

[deplinenoise]

The type checker seems fine with this use of a generic type in a function parameter:

function callMe<T>(value: T, fn: (value: T) => void) : void {
 fn(value);
}

// No error!
callMe(17, (n: string) => console.log(n) );

If callMe is made non-generic and uses hardcoded types then an error is issued as expected:

function callMeConcrete(value: number, fn: (value: number) => void) : void {
 fn(value);
}

// Error as expected!
// TS2345: Argument of type '(n: string) => void' is not assignable to parameter of type '(value: number) => void'.
callMeConcrete(17, (n: string) => console.log(n) );

[RyanCavanaugh]

This was fixed as part of the union types work, see PR #824

[deplinenoise]

Confirmed fix on HEAD - sorry about the noise.

[deplinenoise]

I think I spoke too soon - this still fails to generate an error on HEAD:

function callMe<T>(value: T, fn: (value: T) => void) : void {
 fn(value);
}

callMe([1, "foo"], (n: number[]) => console.log(n) );

[RyanCavanaugh]

That is example considered by design due to function bivariance.

Basically, when we check assignability of a function, we check its parameter types in "both" directions. The type of [1, "foo"] is Array<number|string> so its element type is number|string, and the type number|string is assignable from number, so the check succeeds.

We have an outstanding feature request #222 for turning off function argument type bivariance, which would make this an error.