Overload on constants requires cast for resolution

[NoelAbrahams]

Hi,

TS Version: 1.4

In the following the first call to doFoo fails to compile because the overload resolution algorithm picks the general case:

interface Bar {
    bar?: number;
    baz?: string;
}

interface Foo {
    foo(): string;
}

declare function doFoo(kind: 'Foo', bar?: Bar): Foo;
declare function doFoo(kind: string, bar: any): {}

var x = doFoo('Foo', { bar: 1 });
x.foo(); // Error: Property 'foo' does not exist on type '{}'.

var y = doFoo('Foo', <Bar> { bar: 1 });
y.foo(); // Okay

This is a breaking change because it used to work without the need for the cast in 1.3.

I feel this should compile because { bar: 1 } is compatible with the Bar interface.

[RyanCavanaugh]

Doesn't seem specific to string overloads. This has the potential to break a lot of scenarios.

declare function doFoo(bar?: { baz?: string; bar: number; }): string;
declare function doFoo(bar?: any): number;

var x = doFoo({ bar: 1 }); // x: number, should be x: string
x = 3; // should error

[RyanCavanaugh]

Bisected to 81eaae0 from #919

[ahejlsberg]

@JsonFreeman @RyanCavanaugh @mhegazy I have a proposed fix for this in #1774.

[JsonFreeman]

Here is a similar case without any:

declare function doFoo(bar?: { bar: number; baz?: string; }): string;
declare function doFoo(bar?: { bar: number }): number;

var x = doFoo({ bar: 1 }); // x: number, should be x: string
x = 3; // should error