From a4d947cef00b466f93ed877cea8e556d08a6c359 Mon Sep 17 00:00:00 2001
From: Matthias Moulin <matthias.moulin@gmail.com>
Date: Mon, 27 May 2024 21:15:14 +0200
Subject: [PATCH] Added range_format_string and range_format_debug_string
 formatters

---
 include/fmt/ranges.h | 89 +++++++++++++++++++++++++++++++++-----------
 test/ranges-test.cc  | 29 +++++++++++++++
 2 files changed, 97 insertions(+), 21 deletions(-)

diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index efb37f28f6ca5..ca89258144d0d 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -14,6 +14,9 @@
 #  include <tuple>
 #  include <type_traits>
 #  include <utility>
+#  ifdef __cpp_lib_ranges
+#    include <ranges>
+#  endif
 #endif
 
 #include "format.h"
@@ -171,11 +174,12 @@ template <typename T, typename C> class is_tuple_formattable_<T, C, true> {
   static auto all_true(...) -> std::false_type;
 
   template <size_t... Is>
-  static auto check(index_sequence<Is...>) -> decltype(all_true(
-      index_sequence<Is...>{},
-      integer_sequence<bool,
-                       (is_formattable<typename std::tuple_element<Is, T>::type,
-                                       C>::value)...>{}));
+  static auto check(index_sequence<Is...>)
+      -> decltype(all_true(
+          index_sequence<Is...>{},
+          integer_sequence<
+              bool, (is_formattable<typename std::tuple_element<Is, T>::type,
+                                    C>::value)...>{}));
 
  public:
   static constexpr const bool value =
@@ -335,8 +339,8 @@ struct formatter<Tuple, Char,
   }
 
   template <typename FormatContext>
-  auto format(const Tuple& value, FormatContext& ctx) const
-      -> decltype(ctx.out()) {
+  auto format(const Tuple& value,
+              FormatContext& ctx) const -> decltype(ctx.out()) {
     ctx.advance_to(detail::copy<Char>(opening_bracket_, ctx.out()));
     detail::for_each2(
         formatters_, value,
@@ -516,9 +520,11 @@ template <typename R, typename Char>
 struct formatter<
     R, Char,
     enable_if_t<conjunction<
-        bool_constant<range_format_kind<R, Char>::value !=
-                          range_format::disabled &&
-                      range_format_kind<R, Char>::value != range_format::map>
+        bool_constant<
+            range_format_kind<R, Char>::value != range_format::disabled &&
+            range_format_kind<R, Char>::value != range_format::map &&
+            range_format_kind<R, Char>::value != range_format::string &&
+            range_format_kind<R, Char>::value != range_format::debug_string>
 // Workaround a bug in MSVC 2015 and earlier.
 #if !FMT_MSC_VERSION || FMT_MSC_VERSION >= 1910
         ,
@@ -544,8 +550,8 @@ struct formatter<
   }
 
   template <typename FormatContext>
-  auto format(range_type& range, FormatContext& ctx) const
-      -> decltype(ctx.out()) {
+  auto format(range_type& range,
+              FormatContext& ctx) const -> decltype(ctx.out()) {
     return range_formatter_.format(range, ctx);
   }
 };
@@ -607,6 +613,47 @@ struct formatter<
   }
 };
 
+#ifdef __cpp_lib_ranges
+// A (debug_)string formatter.
+template <typename R, typename Char>
+struct formatter<
+    R, Char,
+    enable_if_t<range_format_kind<R, Char>::value == range_format::string ||
+                range_format_kind<R, Char>::value ==
+                    range_format::debug_string>> {
+ private:
+  using range_type = detail::maybe_const_range<R>;
+  using string_type = conditional_t<
+      std::is_constructible_v<std::basic_string_view<Char>,
+                              std::ranges::iterator_t<range_type>,
+                              std::ranges::sentinel_t<range_type>>,
+      std::basic_string_view<Char>, std::basic_string<Char>>;
+
+  formatter<string_type, Char> underlying_;
+
+ public:
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
+    return underlying_.parse(ctx);
+  }
+
+  template <typename FormatContext>
+  auto format(range_type& range, FormatContext& ctx) const
+      -> decltype(ctx.out()) {
+    auto out = ctx.out();
+    if constexpr (range_format_kind<R, Char>::value ==
+                  range_format::debug_string)
+      *out++ = '\"';
+    out = underlying_.format(
+        string_type{std::ranges::begin(range), std::ranges::end(range)}, ctx);
+    if constexpr (range_format_kind<R, Char>::value ==
+                  range_format::debug_string)
+      *out++ = '\"';
+    return out;
+  }
+};
+#endif
+
 template <typename It, typename Sentinel, typename Char = char>
 struct join_view : detail::view {
   It begin;
@@ -641,8 +688,8 @@ struct formatter<join_view<It, Sentinel, Char>, Char> {
   }
 
   template <typename FormatContext>
-  auto format(view_ref& value, FormatContext& ctx) const
-      -> decltype(ctx.out()) {
+  auto format(view_ref& value,
+              FormatContext& ctx) const -> decltype(ctx.out()) {
     auto it = std::forward<view_ref>(value).begin;
     auto out = ctx.out();
     if (it == value.end) return out;
@@ -684,9 +731,9 @@ auto join(It begin, Sentinel end, string_view sep) -> join_view<It, Sentinel> {
   \endrst
  */
 template <typename Range>
-auto join(Range&& r, string_view sep)
-    -> join_view<decltype(detail::range_begin(r)),
-                 decltype(detail::range_end(r))> {
+auto join(Range&& r,
+          string_view sep) -> join_view<decltype(detail::range_begin(r)),
+                                        decltype(detail::range_end(r))> {
   return {detail::range_begin(r), detail::range_end(r), sep};
 }
 
@@ -817,8 +864,8 @@ FMT_BEGIN_EXPORT
   \endrst
  */
 template <typename... T>
-FMT_CONSTEXPR auto join(const std::tuple<T...>& tuple, string_view sep)
-    -> tuple_join_view<char, T...> {
+FMT_CONSTEXPR auto join(const std::tuple<T...>& tuple,
+                        string_view sep) -> tuple_join_view<char, T...> {
   return {tuple, sep};
 }
 
@@ -834,8 +881,8 @@ FMT_CONSTEXPR auto join(const std::tuple<T...>& tuple, string_view sep)
   \endrst
  */
 template <typename T>
-auto join(std::initializer_list<T> list, string_view sep)
-    -> join_view<const T*, const T*> {
+auto join(std::initializer_list<T> list,
+          string_view sep) -> join_view<const T*, const T*> {
   return join(std::begin(list), std::end(list), sep);
 }
 
diff --git a/test/ranges-test.cc b/test/ranges-test.cc
index e05ae148f55d6..39a16989eee55 100644
--- a/test/ranges-test.cc
+++ b/test/ranges-test.cc
@@ -268,6 +268,35 @@ TEST(ranges_test, disabled_range_formatting_of_path) {
             fmt::range_format::disabled);
 }
 
+struct vector_string : std::vector<char> {
+  using base = std::vector<char>;
+  using base::base;
+};
+struct vector_debug_string : std::vector<char> {
+  using base = std::vector<char>;
+  using base::base;
+};
+FMT_BEGIN_NAMESPACE
+template <>
+struct range_format_kind<vector_string, char>
+    : std::integral_constant<range_format, range_format::string> {};
+template <>
+struct range_format_kind<vector_debug_string, char>
+    : std::integral_constant<range_format, range_format::debug_string> {};
+FMT_END_NAMESPACE
+
+#ifdef __cpp_lib_ranges
+TEST(ranges_test, range_format_string) {
+  const vector_string v{'f', 'o', 'o'};
+  EXPECT_EQ(fmt::format("{}", v), "foo");
+}
+
+TEST(ranges_test, range_format_debug_string) {
+  const vector_debug_string v{'f', 'o', 'o'};
+  EXPECT_EQ(fmt::format("{}", v), "\"foo\"");
+}
+#endif
+
 // A range that provides non-const only begin()/end() to test fmt::join
 // handles that.
 //