Merge pull request #41994 from xedin/fix-score-for-archetype-preference

[CSRanking] Fix a bug in archetype vs. concrete type ranking

Author: xedin

lib/Sema/CSRanking.cpp

@@ -1331,7 +1331,7 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
       continue;
     } else if (type2->is<ArchetypeType>() && !type1->is<ArchetypeType>() &&
                !type1->is<PlaceholderType>()) {
-      ++score2;
+      ++score1;
       continue;
     }
 

test/Constraints/ranking.swift

@@ -410,3 +410,33 @@ func useUnsafePointerStruct<U>(_ ptr: UnsafePointer<U>) {
   // CHECK: function_ref @$s7ranking19UnsafePointerStructVyACSPyxGclufC : $@convention(method) <τ_0_0> (UnsafePointer<τ_0_0>, @thin UnsafePointerStruct.Type) -> UnsafePointerStruct
   let _: UnsafePointerStruct = UnsafePointerStruct(ptr)
 }
+
+/// Archetype vs. non-archetype (expect placeholder)
+
+protocol SignalProtocol {
+  associatedtype Element
+  associatedtype Error: Swift.Error
+}
+
+struct Signal<Element, Error: Swift.Error>: SignalProtocol {
+  init<S: Sequence>(sequence: S) where S.Iterator.Element == Element {
+  }
+}
+
+extension SignalProtocol where Element: SignalProtocol, Element.Error == Error {
+  typealias InnerElement = Element.Element
+
+  func flatten() -> Signal<InnerElement, Error> {
+    fatalError()
+  }
+}
+
+extension SignalProtocol where Element: SignalProtocol, Error == Never {
+  func flatten() -> Signal<Element.Element, Element.Error> {
+    fatalError()
+  }
+}
+
+func no_ambiguity_error_vs_never<Element, Error>(_ signals: [Signal<Element, Error>]) -> Signal<Element, Error> {
+  return Signal(sequence: signals).flatten() // Ok
+}