Open Radar

 
Summary:
A protocol specifying a curried function can be conformed to by a class which uses a normal function return instead. If you try this with a struct or enum, it crashes the compiler.

Steps to Reproduce:
enum S<T> : P {
	func f<T>() -> T -> T {
		return { x in x }
	}
}
protocol P {
	func f<T>()(T) -> T
}

Expected Results:
I expected this would work.

Actual Results:
The compiler crashed.

Regression:
- Doesn’t crash if you use a class.
- Doesn’t crash without the protocol conformance.
- Doesn’t crash if the protocol specifies a normal function return.
- Doesn’t crash if the protocol specifies a normal function return and the value type does a curried return, BUT, you have to explicitly specify the argument labels in the function return in the protocol because the compiler treats it as a labelled tuple; this is pretty frustrating.

Notes:
N/A