Emits broken declaration for class that extends from function that returns a constructor signature.

[rzvc]

TypeScript Version: nightly (2.4.0-dev.20170509)

Code

namespace Test
{
	export interface IFace
	{
	}

	export class SomeClass implements IFace
	{
	}

	export class Derived extends getClass<IFace>()
	{
	}

	export function getClass<T>() : new() => T
	{
		return SomeClass as (new() => T);
	}
}

Expected output:

declare namespace Test {
    interface IFace {
    }
    class SomeClass implements IFace {
    }
    const Derived_base: new () => IFace;
    class Derived extends Derived_base {
    }
    function getClass<T>(): new () => T;
}

Actual behavior:

declare namespace Test {
    interface IFace {
    }
    class SomeClass implements IFace {
    }
    declare const Derived_base: new () => IFace;
    class Derived extends Derived_base {
    }
    function getClass<T>(): new () => T;
}

Notice the extra declare, in front of the "const Derived_base" declaration.
That makes the compiler complain about the declare modifier being inside an already ambient context.

Edit: related to #15572.

[mhegazy]

looks like a regression from #15537