From b0890243138cdba862ee5c86b2b6022e7424c09d Mon Sep 17 00:00:00 2001
From: Caleb Kiage <747955+calebkiage@users.noreply.github.com>
Date: Fri, 19 Jan 2024 16:13:26 +0300
Subject: [PATCH] Fix issue #3817

---
 include/fmt/base.h   | 6 ++++++
 include/fmt/format.h | 1 +
 test/args-test.cc    | 9 +++++++++
 3 files changed, 16 insertions(+)

diff --git a/include/fmt/base.h b/include/fmt/base.h
index 7d75a1bc..860b4aa6 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -773,6 +773,12 @@ template <typename Char> class basic_format_parse_context {
     do_check_arg_id(id);
   }
   FMT_CONSTEXPR void check_arg_id(basic_string_view<Char>) {}
+  FMT_CONSTEXPR void increment_next_id_if_match(int id) {
+    if (next_arg_id_ == id) {
+      // Skip named args.
+      next_arg_id_++;
+    }
+  }
   FMT_CONSTEXPR void check_dynamic_spec(int arg_id);
 };
 
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 8df6c965..5292f5d6 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -4269,6 +4269,7 @@ void vformat_to(buffer<Char>& buf, basic_string_view<Char> fmt,
     FMT_CONSTEXPR auto on_arg_id(basic_string_view<Char> id) -> int {
       int arg_id = context.arg_id(id);
       if (arg_id < 0) report_error("argument not found");
+      parse_context.increment_next_id_if_match(arg_id);
       return arg_id;
     }
 
diff --git a/test/args-test.cc b/test/args-test.cc
index 9c72cb95..2de67f58 100644
--- a/test/args-test.cc
+++ b/test/args-test.cc
@@ -110,6 +110,15 @@ TEST(args_test, named_arg_by_ref) {
   EXPECT_EQ(fmt::vformat("{band}", store), "Rolling Scones");
 }
 
+TEST(args_test, named_with_unnamed) {
+  fmt::dynamic_format_arg_store<fmt::format_context> store;
+  store.push_back(1);
+  store.push_back(fmt::arg("a1", 2));
+  store.push_back(fmt::arg("a2", 3));
+  store.push_back(4);
+  EXPECT_EQ("1 2 3 4", fmt::vformat("{} {a1} {a2} {}", store));
+}
+
 TEST(args_test, named_custom_format) {
   fmt::dynamic_format_arg_store<fmt::format_context> store;
   auto c = custom_type();