Improve separation between code unit types

test/wchar-test.cc

@@ -9,6 +9,18 @@
 
 #include "gtest/gtest.h"
 
+TEST(format_test, vformat_to) {
+  using wcontext = fmt::wformat_context;
+  fmt::basic_format_arg<wcontext> warg = fmt::detail::make_arg<wcontext>(42);
+  auto wargs = fmt::basic_format_args<wcontext>(&warg, 1);
+  auto w = std::wstring();
+  fmt::vformat_to(std::back_inserter(w), L"{}", wargs);
+  EXPECT_EQ(L"42", w);
+  w.clear();
+  fmt::vformat_to(std::back_inserter(w), FMT_STRING(L"{}"), wargs);
+  EXPECT_EQ(L"42", w);
+}
+
 #if FMT_USE_USER_DEFINED_LITERALS
 TEST(format_test, format_udl) {
   using namespace fmt::literals;