Can't inherit from a protocol with primary associated types using the "generic" notation

[tgrapperon]

It doesn't seem possible for a struct to inherit a protocol with primary associated type using this primary associated type in the declaration. In other words, the following doesn't compile:

protocol P<A> {
  associatedtype A
}
struct B {}

struct T: P<B> {} // Error: Cannot inherit from protocol type with generic argument 'P<B>'

This configuration was however explicitly mentioned in SE-0346, so I don't know if this is a bug, a regression, or feature that was not implemented at the end.

Environment

• Swift compiler version info: swift-driver version: 1.62.15 Apple Swift version 5.7.2 (swiftlang-5.7.2.135.5 clang-1400.0.29.51)
• Xcode version info: Version 14.2 (14C18)
• Deployment target: macOS 13.1

[AnthonyLatsis]

It must be that it isn’t implemented yet.

cc @slavapestov

[joshavant]

This works:

protocol P<A> {
  associatedtype A
}
struct B {}

struct T: P {
    typealias A = B
}

[DevAndArtist]

I think this should also be accepted when this issue is fixed:

protocol P<T> {
  associatedtype T
}

struct S {}

class C: P<S> {
  typealias T = S
}