AST: Add TupleType::containsPackExpansionType() utility method

Author: slavapestov

include/swift/AST/Types.h

@@ -2323,6 +2323,8 @@ class TupleType final : public TypeBase, public llvm::FoldingSetNode,
   static void Profile(llvm::FoldingSetNodeID &ID, 
                       ArrayRef<TupleTypeElt> Elements);
 
+  bool containsPackExpansionType() const;
+
 private:
   TupleType(ArrayRef<TupleTypeElt> elements, const ASTContext *CanCtx,
             RecursiveTypeProperties properties)

lib/AST/Type.cpp

@@ -3459,6 +3459,15 @@ int TupleType::getNamedElementId(Identifier I) const {
   return -1;
 }
 
+bool TupleType::containsPackExpansionType() const {
+  for (auto elt : getElements()) {
+    if (elt.getType()->is<PackExpansionType>())
+      return true;
+  }
+
+  return false;
+}
+
 ArchetypeType::ArchetypeType(TypeKind Kind,
                              const ASTContext &Ctx,
                              RecursiveTypeProperties properties,