From db5b8993acc5faea26501489077a094932912129 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Thu, 24 Mar 2022 17:22:44 -0700
Subject: [PATCH] Fix formatting of std::byte via format_as

---
 include/fmt/core.h   | 7 +++++++
 include/fmt/format.h | 6 ------
 test/format-test.cc  | 8 +++++++-
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 3feb2a7d..18c9ae6c 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -8,6 +8,7 @@
 #ifndef FMT_CORE_H_
 #define FMT_CORE_H_
 
+#include <cstddef>  // std::byte
 #include <cstdio>   // std::FILE
 #include <cstring>  // std::strlen
 #include <iterator>
@@ -1275,6 +1276,12 @@ enum { long_short = sizeof(long) == sizeof(int) };
 using long_type = conditional_t<long_short, int, long long>;
 using ulong_type = conditional_t<long_short, unsigned, unsigned long long>;
 
+#ifdef __cpp_lib_byte
+inline auto format_as(std::byte b) -> unsigned char {
+  return static_cast<unsigned char>(b);
+}
+#endif
+
 // Maps formatting arguments to core types.
 // arg_mapper reports errors by returning unformattable instead of using
 // static_assert because it's used in the is_formattable trait.
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 67e5bcca..60e9b3d7 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -34,7 +34,6 @@
 #define FMT_FORMAT_H_
 
 #include <cmath>         // std::signbit
-#include <cstddef>       // std::byte
 #include <cstdint>       // uint32_t
 #include <cstring>       // std::memcpy
 #include <limits>        // std::numeric_limits
@@ -2997,11 +2996,6 @@ constexpr auto format_as(Enum e) noexcept -> underlying_t<Enum> {
 }
 }  // namespace enums
 
-#ifdef __cpp_lib_byte
-inline auto format_as(std::byte b) -> unsigned char { return underlying(b); }
-FMT_FORMAT_AS(std::byte, unsigned char);
-#endif
-
 class bytes {
  private:
   string_view data_;
diff --git a/test/format-test.cc b/test/format-test.cc
index 09553af4..1bee1aa4 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1760,9 +1760,15 @@ TEST(format_test, join) {
 }
 
 #ifdef __cpp_lib_byte
+TEST(format_test, format_byte) {
+  using arg_mapper = fmt::detail::arg_mapper<fmt::format_context>;
+  EXPECT_EQ(arg_mapper().map(std::byte(42)), 42);
+  EXPECT_EQ(fmt::format("{}", std::byte(42)), "42");
+}
+
 TEST(format_test, join_bytes) {
   auto v = std::vector<std::byte>{std::byte(1), std::byte(2), std::byte(3)};
-  EXPECT_EQ("1, 2, 3", fmt::format("{}", fmt::join(v, ", ")));
+  EXPECT_EQ(fmt::format("{}", fmt::join(v, ", ")), "1, 2, 3");
 }
 #endif