From 10cda465edf19ed0303a0655b762ea752f8a0997 Mon Sep 17 00:00:00 2001
From: fhgffy <102001626+fhgffy@users.noreply.github.com>
Date: Thu, 8 Oct 2026 03:32:48 +0800
Subject: [PATCH] Fix output position for compiled variant and expected
 formatting (#4968)

---
 include/fmt/std.h    |  1 +
 test/compile-test.cc | 53 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index ca26905c..2bab00f2 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -143,6 +143,7 @@ FMT_CONSTEXPR auto write_escaped_alternative(OutputIt out, const T& v,
 
   formatter<std::remove_cv_t<T>, Char> underlying;
   maybe_set_debug_format(underlying, true);
+  ctx.advance_to(out);
   return underlying.format(v, ctx);
 }
 #endif
diff --git a/test/compile-test.cc b/test/compile-test.cc
index a5c04ae0..058c0e71 100644
--- a/test/compile-test.cc
+++ b/test/compile-test.cc
@@ -185,6 +185,59 @@ TEST(compile_test, format_to) {
   EXPECT_STREQ("2a", buf);
 }
 
+TEST(compile_test, format_variant) {
+#  ifdef __cpp_lib_variant
+  char buffer[100];
+  auto end =
+      fmt::format_to(buffer, FMT_COMPILE("<{}> {}"), std::variant<int>{42}, 7);
+  EXPECT_EQ("<variant(42)> 7", std::string(buffer, end));
+
+  end =
+      fmt::format_to(buffer, FMT_COMPILE("{}"), std::variant<std::monostate>{});
+  EXPECT_EQ("variant(monostate)", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"),
+                       std::variant<std::variant<int>>{std::variant<int>{42}});
+  EXPECT_EQ("variant(variant(42))", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"),
+                       std::variant<std::string>{"test"});
+  EXPECT_EQ("variant(\"test\")", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"), std::variant<char>{'a'});
+  EXPECT_EQ("variant('a')", std::string(buffer, end));
+#  endif
+}
+
+TEST(compile_test, format_expected) {
+#  ifdef __cpp_lib_expected
+  char buffer[100];
+  auto end = fmt::format_to(buffer, FMT_COMPILE("<{}> {}"),
+                            std::expected<int, int>{42}, 7);
+  EXPECT_EQ("<expected(42)> 7", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"),
+                       std::expected<int, int>{std::unexpected(42)});
+  EXPECT_EQ("unexpected(42)", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"), std::expected<void, int>{});
+  EXPECT_EQ("expected()", std::string(buffer, end));
+
+  end = fmt::format_to(buffer, FMT_COMPILE("{}"),
+                       std::expected<std::string, int>{"test"});
+  EXPECT_EQ("expected(\"test\")", std::string(buffer, end));
+#  endif
+}
+
+TEST(compile_test, format_unexpected) {
+#  ifdef __cpp_lib_expected
+  char buffer[100];
+  auto end = fmt::format_to(buffer, FMT_COMPILE("<{}> {}"),
+                            std::unexpected<int>{42}, 7);
+  EXPECT_EQ("<unexpected(42)> 7", std::string(buffer, end));
+#  endif
+}
+
 TEST(compile_test, format_to_n) {
   constexpr auto buffer_size = 8;
   char buffer[buffer_size];