[ConstraintSystem] Strip pack expansions off of pack reference types in

getUnopenedTypeOfReference.

Author: hborla

lib/Sema/CSBindings.cpp

@@ -1428,9 +1428,6 @@ void PotentialBindings::infer(Constraint *constraint) {
       // Produce a potential binding to the opened element archetype corresponding
       // to the pack type.
       packType = packType->mapTypeOutOfContext();
-      if (auto *expansion = packType->getAs<PackExpansionType>())
-        packType = expansion->getPatternType();
-
       auto *elementEnv = openedElement->getGenericEnvironment();
       auto elementType = elementEnv->mapPackTypeIntoElementContext(packType);
       addPotentialBinding({elementType, AllowedBindingKind::Exact, constraint});

lib/Sema/CSGen.cpp

@@ -3012,8 +3012,7 @@ namespace {
       Type packType;
       if (!expr->getPackElements().empty()) {
         auto packReference = expr->getPackElements().front()->getPackRefExpr();
-        packType = CS.simplifyType(CS.getType(packReference))
-            ->castTo<PackExpansionType>()->getPatternType();
+        packType = CS.simplifyType(CS.getType(packReference));
       } else {
         // FIXME: The generic environment needs to be per-shape-class.
         llvm::SmallVector<GenericEnvironment::PackElementBinding, 2> bindings;

lib/Sema/CSSimplify.cpp

@@ -8613,8 +8613,6 @@ ConstraintSystem::simplifyPackElementOfConstraint(Type first, Type second,
 
   // This constraint only exists to vend bindings.
   auto *packEnv = DC->getGenericEnvironmentOfContext();
-  if (auto *expansion = packType->getAs<PackExpansionType>())
-    packType = expansion->getPatternType();
   if (packType->isEqual(packEnv->mapElementTypeIntoPackContext
                         (elementType->mapTypeOutOfContext()))) {
     return SolutionKind::Solved;

lib/Sema/ConstraintSystem.cpp

@@ -1282,6 +1282,10 @@ Type ConstraintSystem::getUnopenedTypeOfReference(
   Type requestedType =
       getType(value)->getWithoutSpecifierType()->getReferenceStorageReferent();
 
+  // Strip pack expansion types off of pack references.
+  if (auto *expansion = requestedType->getAs<PackExpansionType>())
+    requestedType = expansion->getPatternType();
+
   // Adjust the type for concurrency if requested.
   if (adjustForPreconcurrency)
     requestedType = adjustVarTypeForConcurrency(

test/Constraints/variadic_generic_functions.swift

@@ -27,15 +27,19 @@ func invalidPacks() {
 }
 
 func call() {
-  func multipleParameters<T...>(xs: T..., ys: T...) -> (T...) { return (_: xs) }
+  func multipleParameters<T...>(xs: T..., ys: T...) -> (T...) {
+    return ((each xs)...)
+  }
   multipleParameters()
 
   let x: (_: String) = multipleParameters(xs: "", ys: "")
   let (one, two) = multipleParameters(xs: "", 5.0, ys: "", 5.0)
   multipleParameters(xs: "", 5.0, ys: 5.0, "") // expected-error {{type of expression is ambiguous without more context}}
 
-  func multipleSequences<T..., U...>(xs: T..., ys: U...) -> (T...) { return (_: ys) }
-  // expected-error@-1 {{cannot convert return expression of type '(U...)' to return type '(T...)'}}
+  func multipleSequences<T..., U...>(xs: T..., ys: U...) -> (T...) {
+    return ((each ys)...)
+    // expected-error@-1 {{cannot convert return expression of type '(U...)' to return type '(T...)'}}
+  }
 
   multipleSequences()
   _ = multipleSequences(xs: "", ys: "")