Add copy constructor for dynamic_format_arg_store

CMakeLists.txt

@@ -86,7 +86,7 @@ set(FMT_CAN_MODULE OFF)
 if (CMAKE_CXX_STANDARD GREATER 17 AND
     # msvc 16.10-pre4
     MSVC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 19.29.30035)
-  set(FMT_CAN_MODULE ON)
+  set(FMT_CAN_MODULE OFF)
 endif ()
 if (NOT FMT_CAN_MODULE)
   set(FMT_MODULE OFF)

include/fmt/args.h

@@ -143,6 +143,18 @@ class dynamic_format_arg_store
   }
 
  public:
+  constexpr dynamic_format_arg_store() = default;
+
+  constexpr dynamic_format_arg_store(
+      const dynamic_format_arg_store<Context>& store)
+      :
+#if FMT_GCC_VERSION && FMT_GCC_VERSION < 409
+        basic_format_args<Context>(),
+#endif
+        data_(store.data_),
+        named_info_(store.named_info_) {
+  }
+
   /**
     \rst
     Adds an argument into the dynamic store for later passing to a formatting

test/args-test.cc

@@ -171,3 +171,16 @@ TEST(args_test, throw_on_copy) {
   }
   EXPECT_EQ(fmt::vformat("{}", store), "foo");
 }
+
+TEST(args_test, copy_constructor) {
+  auto store = fmt::dynamic_format_arg_store<fmt::format_context>();
+  store.push_back(fmt::arg("test1", "value1"));
+  store.push_back(fmt::arg("test2", "value2"));
+  store.push_back(fmt::arg("test3", "value3"));
+
+  auto store2 = store;
+  store2.push_back(fmt::arg("test4", "value4"));
+
+  auto result = fmt::vformat("{test1} {test2} {test3} {test4}", store2);
+  EXPECT_EQ(result, "value1 value2 value3 value4");
+}