Add test case for rdar://124697829

This was fixed by 6cd5468.

Author: slavapestov

test/Generics/rdar124697829.swift

@@ -0,0 +1,41 @@
+// RUN: %target-swift-frontend -emit-ir %s -disable-availability-checking
+
+// This is a generics test, but only IRGen exercised the substitution of
+// an abstract conformance with a type parameter -- in the type checker and
+// SIL, we only deal with archetypes.
+
+public protocol IteratorProtocol {
+  associatedtype Element
+}
+
+public protocol Sequence {
+  associatedtype Iterator: IteratorProtocol
+  associatedtype Element where Element == Iterator.Element
+}
+
+public struct IndexingIterator<S: Sequence>: IteratorProtocol {
+  public typealias Element = S.Element
+}
+
+public struct Array<Element>: Sequence {
+  public typealias Iterator = IndexingIterator<Self>
+}
+
+public protocol Publisher {
+  associatedtype Output
+}
+
+public struct SequencePublisher<Elements: Sequence>: Publisher {
+  public typealias Output = Elements.Element
+}
+
+public struct Map<Pub: Publisher, Output>: Publisher {}
+
+public func foo<T>(_: T) -> some Publisher {
+  bar(SequencePublisher<Array<T>>())
+}
+
+public func bar<Pub: Publisher>(_: Pub) -> some Publisher {
+  Map<Pub, Pub.Output>()
+}
+