From 1557ab764422d5087619fea3994012066644a11e Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Fri, 28 Jan 2022 06:31:29 -0800
Subject: [PATCH] Add format_as for enums

---
 include/fmt/core.h | 33 +++++++++++++++++----------------
 test/core-test.cc  | 19 +++++++++++++++++--
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index e27578ed..2da3dc62 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -51,7 +51,7 @@
 
 #ifdef __NVCOMPILER
 #  define FMT_NVCOMPILER_VERSION \
-        (__NVCOMPILER_MAJOR__ * 100 + __NVCOMPILER_MINOR__)
+    (__NVCOMPILER_MAJOR__ * 100 + __NVCOMPILER_MINOR__)
 #else
 #  define FMT_NVCOMPILER_VERSION 0
 #endif
@@ -336,8 +336,8 @@ FMT_BEGIN_DETAIL_NAMESPACE
 // (void)var does not work on many Intel compilers.
 template <typename... T> FMT_CONSTEXPR void ignore_unused(const T&...) {}
 
-constexpr FMT_INLINE auto is_constant_evaluated(bool default_value = false)
-    noexcept -> bool {
+constexpr FMT_INLINE auto is_constant_evaluated(
+    bool default_value = false) noexcept -> bool {
 #ifdef __cpp_lib_is_constant_evaluated
   ignore_unused(default_value);
   return std::is_constant_evaluated();
@@ -443,8 +443,7 @@ template <typename Char> class basic_string_view {
 
   /** Constructs a string reference object from a C string and a size. */
   constexpr basic_string_view(const Char* s, size_t count) noexcept
-      : data_(s),
-        size_(count) {}
+      : data_(s), size_(count) {}
 
   /**
     \rst
@@ -465,13 +464,12 @@ template <typename Char> class basic_string_view {
   template <typename Traits, typename Alloc>
   FMT_CONSTEXPR basic_string_view(
       const std::basic_string<Char, Traits, Alloc>& s) noexcept
-      : data_(s.data()),
-        size_(s.size()) {}
+      : data_(s.data()), size_(s.size()) {}
 
   template <typename S, FMT_ENABLE_IF(std::is_same<
                                       S, detail::std_string_view<Char>>::value)>
-  FMT_CONSTEXPR basic_string_view(S s) noexcept : data_(s.data()),
-                                                      size_(s.size()) {}
+  FMT_CONSTEXPR basic_string_view(S s) noexcept
+      : data_(s.data()), size_(s.size()) {}
 
   /** Returns a pointer to the string data. */
   constexpr auto data() const noexcept -> const Char* { return data_; }
@@ -640,9 +638,7 @@ class basic_format_parse_context : private ErrorHandler {
   /**
     Returns an iterator past the end of the format string range being parsed.
    */
-  constexpr auto end() const noexcept -> iterator {
-    return format_str_.end();
-  }
+  constexpr auto end() const noexcept -> iterator { return format_str_.end(); }
 
   /** Advances the begin iterator to ``it``. */
   FMT_CONSTEXPR void advance_to(iterator it) {
@@ -771,10 +767,8 @@ template <typename T> class buffer {
   FMT_MSC_WARNING(suppress : 26495)
   buffer(size_t sz) noexcept : size_(sz), capacity_(sz) {}
 
-  FMT_CONSTEXPR20 buffer(T* p = nullptr, size_t sz = 0,
-                         size_t cap = 0) noexcept : ptr_(p),
-                                                        size_(sz),
-                                                        capacity_(cap) {}
+  FMT_CONSTEXPR20 buffer(T* p = nullptr, size_t sz = 0, size_t cap = 0) noexcept
+      : ptr_(p), size_(sz), capacity_(cap) {}
 
   FMT_CONSTEXPR20 ~buffer() = default;
   buffer(buffer&&) = default;
@@ -1428,6 +1422,13 @@ template <typename Context> struct arg_mapper {
     return map(static_cast<typename std::underlying_type<T>::type>(val));
   }
 
+  template <typename T, typename U = decltype(format_as(T())),
+            FMT_ENABLE_IF(std::is_enum<T>::value&& std::is_integral<U>::value)>
+  FMT_CONSTEXPR FMT_INLINE auto map(const T& val)
+      -> decltype(std::declval<arg_mapper>().map(U())) {
+    return map(format_as(val));
+  }
+
   FMT_CONSTEXPR FMT_INLINE auto map(detail::byte val) -> unsigned {
     return map(static_cast<unsigned char>(val));
   }
diff --git a/test/core-test.cc b/test/core-test.cc
index c9eea8ff..fc874071 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -755,7 +755,16 @@ template <> struct formatter<convertible_to_pointer_formattable> {
 };
 FMT_END_NAMESPACE
 
-enum class test_scoped_enum {};
+enum class unformattable_scoped_enum {};
+
+namespace test {
+enum class formattable_scoped_enum {};
+auto format_as(formattable_scoped_enum) -> int { return 42; }
+
+struct convertible_to_enum {
+  operator formattable_scoped_enum() const { return {}; }
+};
+}  // namespace test
 
 TEST(core_test, is_formattable) {
 #if 0
@@ -796,7 +805,9 @@ TEST(core_test, is_formattable) {
   struct s;
   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, "");
+  static_assert(!fmt::is_formattable<unformattable_scoped_enum>::value, "");
+  static_assert(fmt::is_formattable<test::formattable_scoped_enum>::value, "");
+  static_assert(!fmt::is_formattable<test::convertible_to_enum>::value, "");
 }
 
 TEST(core_test, format) { EXPECT_EQ(fmt::format("{}", 42), "42"); }
@@ -807,6 +818,10 @@ TEST(core_test, format_to) {
   EXPECT_EQ(s, "42");
 }
 
+TEST(core_test, format_as) {
+  EXPECT_EQ(fmt::format("{}", test::formattable_scoped_enum()), "42");
+}
+
 struct convertible_to_int {
   operator int() const { return 42; }
 };