From 60740b7c24030b9fde5e7288e1cf41aef84fe7ba Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sun, 1 Sep 2024 19:35:00 -0700
Subject: [PATCH] Cleanup base API

---
 include/fmt/base.h   | 30 +++++++++++++-----------------
 include/fmt/ranges.h |  9 +++++++--
 test/base-test.cc    |  9 ---------
 test/format-test.cc  |  4 ++--
 test/ranges-test.cc  |  3 +--
 5 files changed, 23 insertions(+), 32 deletions(-)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index 965ada139201..378d79f94ea2 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -529,6 +529,8 @@ inline FMT_CONSTEXPR20 auto get_container(OutputIt it) ->
 }
 }  // namespace detail
 
+FMT_BEGIN_EXPORT
+
 // Checks whether T is a container with contiguous storage.
 template <typename T> struct is_contiguous : std::false_type {};
 
@@ -539,7 +541,6 @@ template <typename T> struct is_contiguous : std::false_type {};
  * compiled with a different `-std` option than the client code (which is not
  * recommended).
  */
-FMT_EXPORT
 template <typename Char> class basic_string_view {
  private:
   const Char* data_;
@@ -633,7 +634,7 @@ template <typename Char> class basic_string_view {
   }
 };
 
-FMT_EXPORT using string_view = basic_string_view<char>;
+using string_view = basic_string_view<char>;
 
 /// Specifies if `T` is a character type. Can be specialized by users.
 template <typename T> struct is_char : std::false_type {};
@@ -657,28 +658,21 @@ using buffered_context =
     conditional_t<std::is_same<Char, char>::value, context,
                   generic_context<basic_appender<Char>, Char>>;
 
-FMT_EXPORT template <typename Context> class basic_format_arg;
-FMT_EXPORT template <typename Context> class basic_format_args;
-FMT_EXPORT template <typename Context> class dynamic_format_arg_store;
+template <typename Context> class basic_format_arg;
+template <typename Context> class basic_format_args;
+template <typename Context> class dynamic_format_arg_store;
 
 // A separate type would result in shorter symbols but break ABI compatibility
 // between clang and gcc on ARM (#1919).
 using format_args = basic_format_args<context>;
 
 // A formatter for objects of type T.
-FMT_EXPORT
 template <typename T, typename Char = char, typename Enable = void>
 struct formatter {
   // A deleted default constructor indicates a disabled formatter.
   formatter() = delete;
 };
 
-// Specifies if T has an enabled formatter specialization. A type can be
-// formattable even if it doesn't have a formatter e.g. via a conversion.
-template <typename T, typename Context>
-using has_formatter =
-    std::is_constructible<typename Context::template formatter_type<T>>;
-
 // This is defined in base.h instead of format.h to avoid injecting in std.
 // It is a template to avoid undesirable implicit conversions to std::byte.
 #ifdef __cpp_lib_byte
@@ -688,6 +682,8 @@ inline auto format_as(T b) -> unsigned char {
 }
 #endif
 
+FMT_END_EXPORT
+
 namespace detail {
 
 // Constructs fmt::basic_string_view<Char> from types implicitly convertible
@@ -1005,9 +1001,10 @@ template <typename Context> struct arg_mapper {
   }
 
   template <typename T, typename U = remove_const_t<T>>
-  struct formattable : bool_constant<has_const_formatter<U, Context>() ||
-                                     (has_formatter<U, Context>::value &&
-                                      !std::is_const<T>::value)> {};
+  struct formattable
+      : bool_constant<has_const_formatter<U, Context>() ||
+                      (std::is_constructible<formatter<U, char_type>>::value &&
+                       !std::is_const<T>::value)> {};
 
   template <typename T, FMT_ENABLE_IF(formattable<T>::value)>
   FMT_MAP_API auto do_map(T& val) -> T& {
@@ -1790,8 +1787,7 @@ struct compile_string {};
 template <typename T, typename Char>
 FMT_VISIBILITY("hidden")  // Suppress an ld warning on macOS (#3769).
 FMT_CONSTEXPR auto invoke_parse(parse_context<Char>& ctx) -> const Char* {
-  using mapper = arg_mapper<buffered_context<Char>>;
-  using mapped_type = remove_cvref_t<decltype(mapper::map(std::declval<T&>()))>;
+  using mapped_type = remove_cvref_t<mapped_t<T, Char>>;
 #if defined(__cpp_if_constexpr)
   if constexpr (std::is_default_constructible<formatter<mapped_type, Char>>())
     return formatter<mapped_type, Char>().parse(ctx);
diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index cbc12b2a6072..56340e1b50bc 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -358,16 +358,21 @@ template <typename T, typename Char> struct is_range {
 };
 
 namespace detail {
+
+template <typename T, typename Char>
+using has_formatter = std::is_constructible<formatter<T, Char>>;
+
 template <typename Context> struct range_mapper {
   using mapper = arg_mapper<Context>;
+  using char_type = typename Context::char_type;
 
   template <typename T,
-            FMT_ENABLE_IF(has_formatter<remove_cvref_t<T>, Context>::value)>
+            FMT_ENABLE_IF(has_formatter<remove_cvref_t<T>, char_type>::value)>
   static auto map(T&& value) -> T&& {
     return static_cast<T&&>(value);
   }
   template <typename T,
-            FMT_ENABLE_IF(!has_formatter<remove_cvref_t<T>, Context>::value)>
+            FMT_ENABLE_IF(!has_formatter<remove_cvref_t<T>, char_type>::value)>
   static auto map(T&& value) -> decltype(mapper::map(static_cast<T&&>(value))) {
     return mapper::map(static_cast<T&&>(value));
   }
diff --git a/test/base-test.cc b/test/base-test.cc
index 357185d45f0d..3d5a74ab83e1 100644
--- a/test/base-test.cc
+++ b/test/base-test.cc
@@ -604,15 +604,6 @@ template <> struct formatter<enabled_ptr_formatter*> {
 };
 FMT_END_NAMESPACE
 
-TEST(base_test, has_formatter) {
-  using fmt::has_formatter;
-  using context = fmt::format_context;
-  static_assert(has_formatter<enabled_formatter, context>::value, "");
-  static_assert(!has_formatter<disabled_formatter, context>::value, "");
-  static_assert(!has_formatter<disabled_formatter_convertible, context>::value,
-                "");
-}
-
 struct const_formattable {};
 struct nonconst_formattable {};
 
diff --git a/test/format-test.cc b/test/format-test.cc
index 75baa290cce7..6491449ff052 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -2022,8 +2022,8 @@ TEST(format_test, named_arg_udl) {
 TEST(format_test, enum) { EXPECT_EQ(fmt::format("{}", foo), "0"); }
 
 TEST(format_test, formatter_not_specialized) {
-  static_assert(!fmt::has_formatter<fmt::formatter<test_enum>,
-                                    fmt::format_context>::value,
+  static_assert(!fmt::is_formattable<fmt::formatter<test_enum>,
+                                     fmt::format_context>::value,
                 "");
 }
 
diff --git a/test/ranges-test.cc b/test/ranges-test.cc
index 40d545b146ab..0b6c32c16145 100644
--- a/test/ranges-test.cc
+++ b/test/ranges-test.cc
@@ -363,8 +363,7 @@ TEST(ranges_test, enum_range) {
 
 #if !FMT_MSC_VERSION
 TEST(ranges_test, unformattable_range) {
-  EXPECT_FALSE((fmt::has_formatter<std::vector<unformattable>,
-                                   fmt::format_context>::value));
+  EXPECT_FALSE((fmt::is_formattable<std::vector<unformattable>, char>::value));
 }
 #endif