Fix formatting of some nested ranges

include/fmt/ranges.h

@@ -482,7 +482,8 @@ struct range_formatter<
     for (; it != end; ++it) {
       if (i > 0) out = detail::copy_str<Char>(separator_, out);
       ctx.advance_to(out);
-      out = underlying_.format(mapper.map(*it), ctx);
+      auto&& item = *it;
+      out = underlying_.format(mapper.map(item), ctx);
       ++i;
     }
     out = detail::copy_str<Char>(closing_bracket_, out);

test/ranges-test.cc

@@ -7,13 +7,19 @@
 
 #include "fmt/ranges.h"
 
+#include <list>
 #include <map>
+#include <numeric>
 #include <queue>
 #include <stack>
 #include <string>
 #include <utility>
 #include <vector>
 
+#if FMT_HAS_INCLUDE(<ranges>)
+#  include <ranges>
+#endif
+
 #include "gtest/gtest.h"
 
 #if !FMT_GCC_VERSION || FMT_GCC_VERSION >= 601
@@ -242,7 +248,7 @@ template <typename T> class non_const_only_range {
   explicit non_const_only_range(Args&&... args)
       : vec(std::forward<Args>(args)...) {}
 
-  auto begin() -> const_iterator{ return vec.begin(); }
+  auto begin() -> const_iterator { return vec.begin(); }
   auto end() -> const_iterator { return vec.end(); }
 };
 
@@ -360,7 +366,7 @@ struct cpp20_only_range {
     iterator() = default;
     iterator(int i) : val(i) {}
     auto operator*() const -> int { return val; }
-    auto operator++() -> iterator&{
+    auto operator++() -> iterator& {
       ++val;
       return *this;
     }
@@ -378,6 +384,17 @@ struct cpp20_only_range {
 };
 
 static_assert(std::input_iterator<cpp20_only_range::iterator>);
+
+#    ifdef __cpp_lib_ranges_iota
+TEST(ranges_test, nested_ranges) {
+  auto l = std::list{1, 2, 3};
+  auto r = std::views::iota(0, 3) | std::views::transform([&l](auto i) {
+             return std::views::take(std::ranges::subrange(l), i);
+           }) |
+           std::views::transform(std::views::reverse);
+  EXPECT_EQ(fmt::format("{}", r), "[[], [1], [2, 1]]");
+}
+#    endif
 #  endif
 
 TEST(ranges_test, join_sentinel) {