[SR-12736] cannot add constraint 'Self.Model.Float32Components == Self.Model.Float32Components.Model.Float32Components' on 'Self'

[SusanDoggie]

Previous ID	SR-12736
Radar	rdar://problem/62894047
Original Reporter	@SusanDoggie
Type	Bug
Status	Resolved
Resolution	Done

Environment

swift 5.1
swift 5.2.3
Xcode 11.4.1

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, TypeChecker
Assignee	None
Priority	Medium

md5: 81036c9f59b1c54443089757184cc9ce

Issue Description:

The following code will produce a compilation error, but it should not happen.

public protocol ColorModel {
    
    associatedtype Float32Components: ColorComponents where Float32Components.Model == Self, Float32Components.Scalar == Float
    
    init<T: ColorComponents>(_ components: T) where T.Model == Self
    
    var float32Components: Float32Components { get set }
}

public protocol ColorComponents {
    
    associatedtype Model: ColorModel
    
    associatedtype Scalar
    
}

public protocol ColorPixel {
    
    associatedtype Model: ColorModel
    
    init(color: Model, opacity: Double)
    
    init<C: ColorPixel>(_ color: C) where C.Model == Model
}

[beccadax]

@swift-ci create

[typesanitizer]

Seems like a declaration type-checking bug. If I minimize the example:

protocol P1 {
    associatedtype AT1: P2 where AT1.AT2 == Self
}

protocol P2 {
    associatedtype AT2: P1
}

protocol P3 {
    associatedtype AT3: P1
    init<T: P3>(_ t: T) where T.AT3 == AT3 // error: initializer requirement 'init(_:)' cannot add constraint 'Self.AT3.AT1 == Self.AT3.AT1.AT2.AT1' on 'Self'
}

On the other hand, if you add the initializer to an extension with a default implementation, that's fine.

protocol P1 {
    associatedtype AT1: P2 where AT1.AT2 == Self
}

protocol P2 {
    associatedtype AT2: P1
}

protocol P3 {
    associatedtype AT3: P1
}

extension P3 {
    init<T: P3>(_ t: T) where T.AT3 == AT3 {
        fatalError("AAAAA")
    }
}

[SusanDoggie]

I think this bug maybe related to SR-10532

[CodaFi]

The order of constraints matters, though why I'm not quite sure as yet. This compiles:

public protocol ColorModel {
    
    associatedtype Float32Components: ColorComponents where Float32Components.Model == Self, Float32Components.Scalar == Float
    
    init<T: ColorComponents>(_ components: T) where T.Model == Self
    
    var float32Components: Float32Components { get set }
}

public protocol ColorComponents {
    
    associatedtype Model: ColorModel
    
    associatedtype Scalar
    
}

public protocol ColorPixel {
    
    associatedtype Model: ColorModel
    
    init(color: Model, opacity: Double)
    
    init<C: ColorPixel>(_ color: C) where Self.Model == C.Model
}

[slavapestov]

#42113