From 571c02d475708fba0a84d518fdf20587800ccecd Mon Sep 17 00:00:00 2001
From: Vladislav Shchapov <vladislav@shchapov.ru>
Date: Tue, 24 Jun 2025 02:02:11 +0500
Subject: [PATCH] Add xchar support for std::byte formatter (#4480)

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
---
 include/fmt/format.h | 5 +++--
 test/xchar-test.cc   | 7 +++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index 8ee403e8..6a9d8bc6 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -3904,13 +3904,14 @@ constexpr auto format_as(Enum e) noexcept -> underlying_t<Enum> {
 }  // namespace enums
 
 #ifdef __cpp_lib_byte
-template <> struct formatter<std::byte> : formatter<unsigned> {
+template <typename Char>
+struct formatter<std::byte, Char> : formatter<unsigned, Char> {
   static auto format_as(std::byte b) -> unsigned char {
     return static_cast<unsigned char>(b);
   }
   template <typename Context>
   auto format(std::byte b, Context& ctx) const -> decltype(ctx.out()) {
-    return formatter<unsigned>::format(format_as(b), ctx);
+    return formatter<unsigned, Char>::format(format_as(b), ctx);
   }
 };
 #endif
diff --git a/test/xchar-test.cc b/test/xchar-test.cc
index 44b19e87..a94c1bd2 100644
--- a/test/xchar-test.cc
+++ b/test/xchar-test.cc
@@ -171,6 +171,13 @@ TEST(xchar_test, join) {
   EXPECT_EQ(fmt::format(L"({})", fmt::join(t, L", ")), L"(a, 1, 2)");
 }
 
+#ifdef __cpp_lib_byte
+TEST(xchar_test, join_bytes) {
+  auto v = std::vector<std::byte>{std::byte(1), std::byte(2), std::byte(3)};
+  EXPECT_EQ(fmt::format(L"{}", fmt::join(v, L", ")), L"1, 2, 3");
+}
+#endif
+
 enum streamable_enum {};
 
 std::wostream& operator<<(std::wostream& os, streamable_enum) {