From e281749c5de4c69dce12f78ec5ceb08ede49a8c9 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sat, 9 Mar 2024 08:20:27 -0800
Subject: [PATCH] Simplify range formatter

---
 include/fmt/base.h | 10 ++++++----
 test/base-test.cc  | 12 ++++++------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index 9bbf88fd..6dedd4ec 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -2961,8 +2961,8 @@ template <typename OutputIt, typename Sentinel = OutputIt>
 struct format_to_result {
   /** Iterator pointing to just after the last successful write in the range. */
   OutputIt out;
-  /** Sentinel indicating the end of the output range. */
-  Sentinel out_last;
+  /** Specifies if the output was truncated. */
+  bool truncated;
 
   FMT_CONSTEXPR operator OutputIt&() & noexcept { return out; }
   FMT_CONSTEXPR operator const OutputIt&() const& noexcept { return out; }
@@ -2974,13 +2974,15 @@ struct format_to_result {
 template <size_t N>
 auto vformat_to(char (&out)[N], string_view fmt, format_args args)
     -> format_to_result<char*> {
-  return {vformat_to_n(out, N, fmt, args).out, out + N};
+  auto result = vformat_to_n(out, N, fmt, args);
+  return {result.out, result.size > N};
 }
 
 template <size_t N, typename... T>
 FMT_INLINE auto format_to(char (&out)[N], format_string<T...> fmt, T&&... args)
     -> format_to_result<char*> {
-  return vformat_to(out, fmt, fmt::make_format_args(args...));
+  auto result = fmt::format_to_n(out, N, fmt, static_cast<T&&>(args)...);
+  return {result.out, result.size > N};
 }
 
 /** Returns the number of chars in the output of ``format(fmt, args...)``. */
diff --git a/test/base-test.cc b/test/base-test.cc
index 1a9776c8..b8ec60d8 100644
--- a/test/base-test.cc
+++ b/test/base-test.cc
@@ -697,13 +697,13 @@ TEST(core_test, format_to_c_array) {
   char buffer[4];
   auto result = fmt::format_to(buffer, "{}", 12345);
   EXPECT_EQ(4, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(0, std::distance(result.out, result.out_last));
+  EXPECT_TRUE(result.truncated);
   EXPECT_EQ(buffer + 4, result.out);
   EXPECT_EQ("1234", fmt::string_view(buffer, 4));
 
   result = fmt::format_to(buffer, "{:s}", "foobar");
   EXPECT_EQ(4, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(0, std::distance(result.out, result.out_last));
+  EXPECT_TRUE(result.truncated);
   EXPECT_EQ(buffer + 4, result.out);
   EXPECT_EQ("foob", fmt::string_view(buffer, 4));
 
@@ -713,24 +713,24 @@ TEST(core_test, format_to_c_array) {
   buffer[3] = 'x';
   result = fmt::format_to(buffer, "{}", 'A');
   EXPECT_EQ(1, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(3, std::distance(result.out, result.out_last));
+  EXPECT_FALSE(result.truncated);
   EXPECT_EQ(buffer + 1, result.out);
   EXPECT_EQ("Axxx", fmt::string_view(buffer, 4));
 
   result = fmt::format_to(buffer, "{}{} ", 'B', 'C');
   EXPECT_EQ(3, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(1, std::distance(result.out, result.out_last));
+  EXPECT_FALSE(result.truncated);
   EXPECT_EQ(buffer + 3, result.out);
   EXPECT_EQ("BC x", fmt::string_view(buffer, 4));
 
   result = fmt::format_to(buffer, "{}", "ABCDE");
   EXPECT_EQ(4, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(0, std::distance(result.out, result.out_last));
+  EXPECT_TRUE(result.truncated);
   EXPECT_EQ("ABCD", fmt::string_view(buffer, 4));
 
   result = fmt::format_to(buffer, "{}", std::string(1000, '*'));
   EXPECT_EQ(4, std::distance(&buffer[0], result.out));
-  EXPECT_EQ(0, std::distance(result.out, result.out_last));
+  EXPECT_TRUE(result.truncated);
   EXPECT_EQ("****", fmt::string_view(buffer, 4));
 }