IRGen: Handle PackArchetypeType in getExemplarArchetype()

Author: slavapestov

lib/IRGen/GenType.cpp

@@ -1966,14 +1966,14 @@ const TypeInfo &TypeConverter::getCompleteTypeInfo(CanType T) {
 }
 
 ArchetypeType *TypeConverter::getExemplarArchetype(ArchetypeType *t) {
-  // Get the primary archetype.
-  auto root = t->getRoot();
-
-  // If there is no primary (IOW, it's an opened archetype), the archetype is
-  // an exemplar.
-  if (!isa<PrimaryArchetypeType>(root) && !isa<VariadicSequenceType>(root))
+  if (isa<LocalArchetypeType>(t) || isa<OpaqueTypeArchetypeType>(t))
     return t;
 
+  assert(isa<PrimaryArchetypeType>(t) || isa<PackArchetypeType>(t));
+
+  // Get the root archetype.
+  auto root = t->getRoot();
+
   // Retrieve the generic environment of the archetype.
   auto genericEnv = root->getGenericEnvironment();
 

test/IRGen/pack_archetype_canonicalization.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend -emit-ir %s -enable-experimental-feature VariadicGenerics
+
+// Because of -enable-experimental-feature VariadicGenerics
+// REQUIRES: asserts
+
+// This would crash.
+public struct G<T> {}
+
+public struct GG<each T> {
+  public var variables: (repeat G<each T>)
+
+  public init() {
+    fatalError()
+  }
+}