Type inference failure on generic type with multiple optional properties

[Nemo157]

interface Client {
    wrap<T>(interceptor: Interceptor<T>, config?: T): Client;
    typedWrap(interceptor: Interceptor<Config>, config?: Config): Client;
}

interface Interceptor<T> {
    parent(client?: Client, config?: T): Client;
}

interface Config {
    mime?: string;
    accept?: string;
}

var client: Client;
var config: Config = { mime: 'application/json' };
var mime: Interceptor<Config>;

client.wrap(mime, config);
client.wrap(mime, { mime: 'application/json' });

client.typedWrap(mime, config);
client.typedWrap(mime, { mime: 'application/json' });

with tsc version 1.4.1.0 gives

test.ts(20,1): error TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
  Type argument candidate 'Config' is not a valid type argument because it is not a supertype of candidate '{ mime: string; }'.

I can't tell exactly what's going wrong here, but it appears to be some issue at the intersection between generics and plain objects implementing interfaces. I would assume by the fact that both assigning the object to a typed variable and using a specified type in the function that Config is in fact a supertype of the candidate; this fact is just not being picked up during the type inference stage.

[Nemo157]

And by the looks of it this may already be fixed in #1795 😄.

[ahejlsberg]

Yes, #1795 does indeed fix this. It is the same problem reported in #1446.