From 5cc5072aa68c48a8c67f4d09ef1b9fcb9ab15a26 Mon Sep 17 00:00:00 2001
From: Soumik15630m <soumik15630m@gmail.com>
Date: Fri, 30 Jan 2026 20:09:00 +0530
Subject: [PATCH] Fix range suppresor formatter (#4660)

---
 include/fmt/ranges.h | 12 ++++++++++--
 test/ranges-test.cc  | 30 ++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index 89cdbc80..d67f59af 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -746,7 +746,6 @@ struct formatter<tuple_join_view<Tuple, Char>, Char,
     return do_format(value, ctx, std::integral_constant<size_t, N - 1>());
   }
 };
-
 namespace detail {
 // Check if T has an interface like a container adaptor (e.g. std::stack,
 // std::queue, std::priority_queue).
@@ -766,10 +765,19 @@ template <typename Container> struct all {
 };
 }  // namespace detail
 
+/**
+ * returns "true" if "T" is a container adaptor (like "std::stack")
+ * that should be formatted by iterating over the underlying container.
+ * */
+
+FMT_EXPORT
+template <typename T>
+struct is_container_adaptor : detail::is_container_adaptor_like<T> {};
+
 template <typename T, typename Char>
 struct formatter<
     T, Char,
-    enable_if_t<conjunction<detail::is_container_adaptor_like<T>,
+    enable_if_t<conjunction<is_container_adaptor<T>,
                             bool_constant<range_format_kind<T, Char>::value ==
                                           range_format::disabled>>::value>>
     : formatter<detail::all<typename T::container_type>, Char> {
diff --git a/test/ranges-test.cc b/test/ranges-test.cc
index d65037fa..f82569b2 100644
--- a/test/ranges-test.cc
+++ b/test/ranges-test.cc
@@ -797,3 +797,33 @@ struct not_range {
   void end() const {}
 };
 static_assert(!fmt::is_formattable<not_range>{}, "");
+
+namespace test_detail {
+  template <typename T>
+  struct partial_opt_out_wrapper {
+    using container_type = std::vector<T>;
+    std::vector<T> c = {1, 2, 3};
+  };
+}  // namespace test_detail
+
+namespace fmt {
+  template <typename T>
+  struct is_container_adaptor<test_detail::partial_opt_out_wrapper<T>> : std::false_type {};
+
+  template <typename T>
+  struct formatter<test_detail::partial_opt_out_wrapper<T>> {
+    constexpr fmt::format_parse_context::iterator parse(fmt::format_parse_context& ctx) const {
+      return ctx.begin();
+    }
+
+    fmt::format_context::iterator format(const test_detail::partial_opt_out_wrapper<T>& val,
+                                         fmt::format_context& ctx) const {
+      return fmt::format_to(ctx.out(), "PartialOptOut(size={})", val.c.size());
+    }
+  };
+}  // namespace fmt
+
+TEST(ranges_test, container_adaptor_partial_specialization) {
+  test_detail::partial_opt_out_wrapper<int> obj;
+  EXPECT_EQ(fmt::format("{}", obj), "PartialOptOut(size=3)");
+}
\ No newline at end of file