From d09b5c14531f361dad2fae7ee7dfc284672eb5e2 Mon Sep 17 00:00:00 2001
From: Alexey Ochapov <alexez@alexez.com>
Date: Sun, 27 Dec 2020 18:23:28 +0300
Subject: [PATCH] Fix std::byte formatting with compile-time API (#2072)

* add test for byte formatting with `FMT_COMPILE`

* fix byte formatting with `FMT_COMPILE`, use `__cpp_lib_byte` macro

* use is not custom mapped type check

* workaround MSVC bug
---
 include/fmt/format.h | 13 +++++++++----
 test/compile-test.cc |  3 +++
 test/format-test.cc  |  2 +-
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index 580e9f29..3d18b9e1 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2113,9 +2113,14 @@ FMT_CONSTEXPR OutputIt write(OutputIt out, T value) {
   return base_iterator(out, it);
 }
 
-template <typename Char, typename OutputIt, typename T,
-          FMT_ENABLE_IF(std::is_enum<T>::value &&
-                        !std::is_same<T, Char>::value)>
+// FMT_ENABLE_IF() condition separated to workaround MSVC bug
+template <
+    typename Char, typename OutputIt, typename T,
+    bool check =
+        std::is_enum<T>::value && !std::is_same<T, Char>::value &&
+        mapped_type_constant<T, basic_format_context<OutputIt, Char>>::value !=
+            type::custom_type,
+    FMT_ENABLE_IF(check)>
 FMT_CONSTEXPR OutputIt write(OutputIt out, T value) {
   return write<Char>(
       out, static_cast<typename std::underlying_type<T>::type>(value));
@@ -3570,7 +3575,7 @@ 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::std_string_view<Char>, basic_string_view<Char>);
-#if __cplusplus >= 201703L
+#ifdef __cpp_lib_byte
 FMT_FORMAT_AS(std::byte, unsigned);
 #endif
 
diff --git a/test/compile-test.cc b/test/compile-test.cc
index c2e1ec1c..df76f085 100644
--- a/test/compile-test.cc
+++ b/test/compile-test.cc
@@ -130,6 +130,9 @@ TEST(CompileTest, FormatDefault) {
   EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), "foo"));
   EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), std::string("foo")));
   EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), test_formattable()));
+#  ifdef __cpp_lib_byte
+  EXPECT_EQ("42", fmt::format(FMT_COMPILE("{}"), std::byte{42}));
+#  endif
 }
 
 TEST(CompileTest, FormatWideString) {
diff --git a/test/format-test.cc b/test/format-test.cc
index 81bc406f..e821e773 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1762,7 +1762,7 @@ TEST(FormatTest, JoinArg) {
 #endif
 }
 
-#if __cplusplus >= 201703L
+#ifdef __cpp_lib_byte
 TEST(FormatTest, JoinBytes) {
   std::vector<std::byte> v = {std::byte(1), std::byte(2), std::byte(3)};
   EXPECT_EQ("1, 2, 3", fmt::format("{}", fmt::join(v, ", ")));