[SR-8705] Attempt to use same type requirement in the method description causes compiler error

[swift-ci]

Previous ID	SR-8705
Radar	None
Original Reporter	spiceginger (JIRA User)
Type	Bug

Attachment: Download

Additional Detail from JIRA

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

md5: 8df8fbcda4ed1cc019b6f866dad7f962

Issue Description:

import UIKit

protocol Factory {
    
    associatedtype ViewController: UIViewController
    
    associatedtype Context

    func build(with context: Context) -> ViewController

}

struct NavigationFactory: Factory {
    
    func build(with context: Any?) -> UINavigationController {
        return UINavigationController(nibName: nil, bundle: nil)
    }
    
}

struct Duplicator<VC: UIViewController, C>: Factory {
    typealias ViewController = VC
    typealias Context = C
    func build(with context: Context) -> ViewController {
        return ViewController(nibName: nil, bundle: nil)
    }
}

struct MergerWorks<F1: Factory, F2: Factory> where F1.ViewController == F2.ViewController, F1.Context == F2.Context {
    let vc1: UIViewController
    let vc2: UIViewController
    init(factory1: F1, factory2:F2, context: F1.Context) {
        self.vc1 = factory1.build(with: context)
        self.vc2 = factory2.build(with: context)
    }
}

struct MergerBroken  {
    let vc1: UIViewController
    let vc2: UIViewController
    init<F1: Factory, F2: Factory>(factory1: F1, factory2:F2, context: F1.Context) where F1.ViewController == F2.ViewController, F1.Context == F2.Context {
        self.vc1 = factory1.build(with: context)
        self.vc2 = factory2.build(with: context)
    }
    
}

let mergerWorks = MergerWorks(factory1: NavigationFactory(), factory2: Duplicator(), context: nil)
let mergerBroken = MergerBroken(factory1: NavigationFactory(), factory2: Duplicator(), context: nil) // Causes error: error: generic parameter 'C' could not be inferred, note: explicitly specify the generic arguments to fix this issue

Implicitly specifying the type of `Duplicator` helps:

let mergerBroken = MergerBroken(factory1: NavigationFactory(), factory2: Duplicator<UINavigationController, Any?>(), context: nil)

But expected the same behaviour as in MergerWorks where compiler is able to resolve the type of Duplicator.

[swift-ci]

Comment by Evgeny Kaz (JIRA)

cc @DougGregor