Open Radar

 
Summary:
This is a wooly one that I can‘t really describe more succinctly, so just write these files and compile them and enjoy the stack trace.


File one:

protocol C : Collection {}

extension Array : C {}


File two:

struct A<T> {
	let a: B<Array<T>>
	
	init() {
		a = B()
	}
}

struct B<T : Collection> {}


Weirdest corner case I’ve seen yet, but not the only one I’ve seen involving Collection.


Steps to Reproduce:
Put these two files in a project and build.


Expected Results:
I expected it to compile.


Actual Results:
The compiler crashed.


Regression:
There are many workarounds:

1. Put these both into a single file
2. Don’t constrain B<T>’s parameter to Collection
3. Remove A’s property a
4. Parameterize A’s property a by any other type conformed to C
5. Don’t write the init method for A
6. Conform C to Printable instead
7. Don’t conform C to any protocol
8. Don’t extend Array to conform to C


Notes:
Sample project will be uploaded shortly. Thank you for bearing with me.