Merge pull request swiftlang#33538 from slavapestov/regression-test-rdar62268062

Add regression test for rdar://problem/62268062

Author: slavapestov

validation-test/compiler_crashers_2_fixed/rdar62268062.swift

@@ -0,0 +1,41 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+public protocol HorseSaddle {}
+public enum EnglishSaddle : HorseSaddle {}
+
+public enum WesternSaddle<A, B> : HorseSaddle {}
+
+public protocol Horse {
+    associatedtype Body : Horse
+
+    associatedtype Saddle: HorseSaddle
+
+    var body: Body { get }
+}
+
+extension Horse {
+    typealias Saddle = Body.Saddle
+}
+
+public struct DraftHorse<T> : Pony {
+    public typealias Saddle = EnglishSaddle
+    public typealias Body = Never
+    var contents: T
+}
+
+// MARK: - Implementation detail
+
+extension Never : Horse {
+    public typealias Saddle = EnglishSaddle
+    public typealias Body = Never
+
+    public var body: Never {
+        switch self {}
+    }
+}
+
+protocol Pony : Horse where Body == Never {}
+extension Pony {
+    public var body: Never { fatalError() }
+}
+