[Tests] NFC: Add a test-case for regression when TypeSubstituter::transformSubstitutionMap() is enabled

Author: xedin

test/Generics/rdar158774099.swift

@@ -0,0 +1,74 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -typecheck -verify \
+// RUN:     %t/View.swift %t/Modifier.swift %t/MyStorage.swift %t/Storage.swift %t/WrappedStorage.swift
+
+//--- Storage.swift
+
+protocol Representable {
+  associatedtype Outputs
+  typealias Context = RepresentableContext<Self>
+}
+
+struct RepresentableContext<R: Representable> {}
+
+struct Inputs<Outputs> {
+}
+
+protocol Storage<Value> {
+  associatedtype Value
+  associatedtype R: Representable
+
+  func body(content: Content) -> Value
+
+  typealias Content = Inputs<R.Outputs>
+}
+
+//--- WrappedStorage.swift
+private struct WrappedStorage<Base: Storage>: Storage where Base.Value == MyStorage.Value {
+  typealias R = Base.R
+
+  init(base: Base, body: @escaping (Base.Value) -> Void) {
+  }
+
+  func body(content: Content) -> Base.Value { fatalError() }
+}
+
+extension Storage where Value == MyStorage.Value {
+  func withStorage(body: @escaping (Value) -> Void) -> some Storage<Value> {
+    WrappedStorage(base: self, body: body)
+  }
+}
+
+//--- MyStorage.swift
+struct MyRepresentable: Representable {
+  struct Outputs {}
+}
+
+struct MyStorage: Storage {
+  typealias R = MyRepresentable
+
+  struct Value: Equatable {}
+
+  func body(content: Content) -> Value {
+    fatalError()
+  }
+}
+
+//--- Modifier.swift
+extension P {
+  func storage(_: some Storage) -> some P { Test() }
+}
+
+//--- View.swift
+protocol P {
+}
+
+struct Test: P {
+}
+
+func test() -> some P {
+  let storage = MyStorage().withStorage { value in }
+  return Test().storage(storage)
+}