Class without setter property incorrectly allowed to implement interface

[MastroLindus]

TypeScript Version: reproduced on 2.7.0-dev, and on 2.2.1

Code

interface A {
  readonly foo: string;
}

interface B {
  foo: string;
}

class C implements A,B {
  public get foo() { return "bla";}
}

const baz = (p: B) => p.foo = "blabla";

baz(new C());

Expected behavior:
-Compiler complains that C doesn't implement properly B since it has no setter (and now we have a proper way to define an interface with a readonly property as A shows).
-Compiler complains if you try to pass a C to function baz.

In general with or without the "implements" declaration, C should not be assignable to B if it doesn't implement a setter for foo.

Actual behavior:
No Compile Errors.
Runtime error when baz tries to set the foo property.

I am not really sure this is a bug or some design choice, but I would definitely expect the type system to catch this, especially since we have the "readonly" keyword to mark properties that cannot be set.

[mhegazy]

Please see #13347

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.