From 486e7ba579a2c677772d004ecd0311142ba481be Mon Sep 17 00:00:00 2001
From: Oleksandr Koval <37271580+OleksandrKvl@users.noreply.github.com>
Date: Fri, 3 Oct 2025 14:40:44 +0300
Subject: [PATCH] support `std::optional` holding cv-qualified types (#4562)

Fixes #4561
---
 include/fmt/std.h | 2 +-
 test/std-test.cc  | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index 945dee5b..e32d82f5 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -353,7 +353,7 @@ template <typename T, typename Char>
 struct formatter<std::optional<T>, Char,
                  std::enable_if_t<is_formattable<T, Char>::value>> {
  private:
-  formatter<T, Char> underlying_;
+  formatter<std::remove_cv_t<T>, Char> underlying_;
   static constexpr basic_string_view<Char> optional =
       detail::string_literal<Char, 'o', 'p', 't', 'i', 'o', 'n', 'a', 'l',
                              '('>{};
diff --git a/test/std-test.cc b/test/std-test.cc
index f5b4e7e8..4bd8abce 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -145,6 +145,7 @@ TEST(std_test, optional) {
   EXPECT_FALSE((fmt::is_formattable<unformattable>::value));
   EXPECT_FALSE((fmt::is_formattable<std::optional<unformattable>>::value));
   EXPECT_TRUE((fmt::is_formattable<std::optional<int>>::value));
+  EXPECT_TRUE((fmt::is_formattable<std::optional<const int>>::value));
 #endif
 }