From ba36a04811c5f73681a8e1c1e28539182e6a211b Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Mon, 22 Jul 2024 16:01:18 -0700
Subject: [PATCH] Remove counting_iterator

---
 include/fmt/base.h    |  2 +-
 include/fmt/compile.h |  9 ++-------
 include/fmt/format.h  | 46 +++++--------------------------------------
 test/compile-test.cc  |  8 --------
 4 files changed, 8 insertions(+), 57 deletions(-)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index 57750ca7..19cf4916 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -1103,7 +1103,7 @@ template <typename T = char> class counting_buffer : public buffer<T> {
   }
 
  public:
-  counting_buffer() : buffer<T>(grow, data_, 0, buffer_size) {}
+  FMT_CONSTEXPR counting_buffer() : buffer<T>(grow, data_, 0, buffer_size) {}
 
   auto count() -> size_t { return count_ + this->size(); }
 };
diff --git a/include/fmt/compile.h b/include/fmt/compile.h
index b33a40db..8a632f63 100644
--- a/include/fmt/compile.h
+++ b/include/fmt/compile.h
@@ -21,12 +21,6 @@ FMT_EXPORT class compiled_string {};
 
 namespace detail {
 
-template <typename T, typename InputIt>
-FMT_CONSTEXPR inline auto copy(InputIt begin, InputIt end, counting_iterator it)
-    -> counting_iterator {
-  return it + (end - begin);
-}
-
 template <typename S>
 struct is_compiled_string : std::is_base_of<compiled_string, S> {};
 
@@ -496,7 +490,8 @@ template <typename S, typename... Args,
           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
 auto formatted_size(const S& fmt, const Args&... args) -> size_t {
   auto buf = detail::counting_buffer<>();
-  return fmt::format_to(fmt::appender(buf), fmt, args...).count();
+  fmt::format_to(appender(buf), fmt, args...);
+  return buf.count();
 }
 
 template <typename S, typename... Args,
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 10a8fbcc..610cb9b9 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2235,46 +2235,6 @@ FMT_CONSTEXPR FMT_INLINE auto write(OutputIt out, T value,
                          loc);
 }
 
-// An output iterator that counts the number of objects written to it and
-// discards them.
-class counting_iterator {
- private:
-  size_t count_;
-
- public:
-  using iterator_category = std::output_iterator_tag;
-  using difference_type = std::ptrdiff_t;
-  using pointer = void;
-  using reference = void;
-  FMT_UNCHECKED_ITERATOR(counting_iterator);
-
-  struct value_type {
-    template <typename T> FMT_CONSTEXPR void operator=(const T&) {}
-  };
-
-  FMT_CONSTEXPR counting_iterator() : count_(0) {}
-
-  FMT_CONSTEXPR auto count() const -> size_t { return count_; }
-
-  FMT_CONSTEXPR auto operator++() -> counting_iterator& {
-    ++count_;
-    return *this;
-  }
-  FMT_CONSTEXPR auto operator++(int) -> counting_iterator {
-    auto it = *this;
-    ++*this;
-    return it;
-  }
-
-  FMT_CONSTEXPR friend auto operator+(counting_iterator it, difference_type n)
-      -> counting_iterator {
-    it.count_ += static_cast<size_t>(n);
-    return it;
-  }
-
-  FMT_CONSTEXPR auto operator*() const -> value_type { return {}; }
-};
-
 template <typename Char, typename OutputIt>
 FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
                          const format_specs& specs) -> OutputIt {
@@ -2285,7 +2245,11 @@ FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
   bool is_debug = specs.type == presentation_type::debug;
   size_t width = 0;
 
-  if (is_debug) size = write_escaped_string(counting_iterator{}, s).count();
+  if (is_debug) {
+    auto buf = counting_buffer<Char>();
+    write_escaped_string(basic_appender<Char>(buf), s);
+    size = buf.count();
+  }
 
   if (specs.width != 0) {
     if (is_debug)
diff --git a/test/compile-test.cc b/test/compile-test.cc
index ff2d573b..e44eee9f 100644
--- a/test/compile-test.cc
+++ b/test/compile-test.cc
@@ -14,14 +14,6 @@
 #include "gmock/gmock.h"
 #include "gtest-extra.h"
 
-TEST(iterator_test, counting_iterator) {
-  auto it = fmt::detail::counting_iterator();
-  auto prev = it++;
-  EXPECT_EQ(prev.count(), 0);
-  EXPECT_EQ(it.count(), 1);
-  EXPECT_EQ((it + 41).count(), 42);
-}
-
 TEST(compile_test, compile_fallback) {
   // FMT_COMPILE should fallback on runtime formatting when `if constexpr` is
   // not available.