From fd62fba9855c9cf8fe17eb9363e03f93563d9dc3 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Thu, 9 Dec 2021 11:11:17 -0800
Subject: [PATCH] Don't convert scoped enums to integers

---
 include/fmt/core.h   | 10 ++++++++++
 include/fmt/format.h |  1 +
 test/core-test.cc    |  3 +++
 test/ranges-test.cc  |  2 +-
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index e87b706c4b85..179adab1247f 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>
 #include <iterator>
@@ -367,6 +368,12 @@ FMT_NORETURN FMT_API void assert_fail(const char* file, int line,
 #  endif
 #endif
 
+#ifdef __cpp_lib_byte
+using byte = std::byte;
+#else
+enum class byte : unsigned char {};
+#endif
+
 #if defined(FMT_USE_STRING_VIEW)
 template <typename Char> using std_string_view = std::basic_string_view<Char>;
 #elif defined(FMT_USE_EXPERIMENTAL_STRING_VIEW)
@@ -1403,6 +1410,9 @@ template <typename Context> struct arg_mapper {
 
   template <typename T,
             FMT_ENABLE_IF(std::is_enum<T>::value &&
+                          (std::is_convertible<T, int>::value
+                           || std::is_same<T, detail::byte>::value
+                           ) &&
                           !has_formatter<T, Context>::value &&
                           !has_fallback_formatter<T, char_type>::value)>
   FMT_CONSTEXPR FMT_INLINE auto map(const T& val)
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 0678f229b21b..08fba7ca13a5 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2606,6 +2606,7 @@ FMT_FORMAT_AS(unsigned long, unsigned long long);
 FMT_FORMAT_AS(Char*, const Char*);
 FMT_FORMAT_AS(std::basic_string<Char>, basic_string_view<Char>);
 FMT_FORMAT_AS(std::nullptr_t, const void*);
+FMT_FORMAT_AS(detail::byte, unsigned char);
 FMT_FORMAT_AS(detail::std_string_view<Char>, basic_string_view<Char>);
 
 template <typename Char>
diff --git a/test/core-test.cc b/test/core-test.cc
index decf31a744e8..78ec3de26523 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -737,6 +737,8 @@ struct convertible_to_pointer {
   operator const int*() const { return nullptr; }
 };
 
+enum class test_scoped_enum {};
+
 TEST(core_test, is_formattable) {
   static_assert(fmt::is_formattable<signed char*>::value, "");
   static_assert(fmt::is_formattable<unsigned char*>::value, "");
@@ -777,6 +779,7 @@ TEST(core_test, is_formattable) {
 
   static_assert(!fmt::is_formattable<int(s::*)>::value, "");
   static_assert(!fmt::is_formattable<int (s::*)()>::value, "");
+  static_assert(!fmt::is_formattable<test_scoped_enum>::value, "");
 }
 
 TEST(core_test, format) { EXPECT_EQ(fmt::format("{}", 42), "42"); }
diff --git a/test/ranges-test.cc b/test/ranges-test.cc
index f8e67390d6e2..de785c0f511f 100644
--- a/test/ranges-test.cc
+++ b/test/ranges-test.cc
@@ -190,7 +190,7 @@ TEST(ranges_test, range) {
   EXPECT_EQ(fmt::format("{}", z), "[0, 0, 0]");
 }
 
-enum class test_enum { foo };
+enum test_enum { foo };
 
 TEST(ranges_test, enum_range) {
   auto v = std::vector<test_enum>{test_enum::foo};