Issue Description:

• • Struct.swift --

    struct Struct {
        private var _property = Wrapper<Property?>()
        var isArray: Bool { _property.isArray }
    }

  • main.swift --

    protocol Protocol {
        associatedtype ElementValue: Singular
        static var isArray: Bool { get }
    }
    
    protocol Singular: Equatable, NonOptional {
        associatedtype ElementValue = Self
    }
    
    extension Singular {
        static var isArray: Bool { false }
        public static func == (lhs: Self, rhs: Self) -> Bool {
            fatalError()
        }
    }
    
    protocol NonOptional: Protocol {
        associatedtype ElementValue = Self
    }
    
    extension Optional: Protocol where Wrapped: NonOptional {
        typealias ElementValue = Wrapped.ElementValue
        static var isArray: Bool { Wrapped.isArray }
    }
    
    struct Wrapper <T: Protocol> {
        var wrappedValue: T { fatalError() }
        var isArray: Bool { T.isArray }
    }
    
    struct Property {
        var value: Int
    }
    
    extension Property: Singular { }
    
    assert(Struct().isArray == false)

    Above source compiles fine but crashes at runtime. The title may be misleading. Actually if we perform any of the below actions, the program executes as expected:

1. Combine the source code into one single file (move `Struct` definition either to the top or bottom of `main.swift`).

2. Remove `Equatable`

3. Remove `ElementValue` typealias & associatedtype