From dad3237514e53b5e163b3bb9153f1edbc2db9738 Mon Sep 17 00:00:00 2001
From: Vladislav Shchapov <vladislav@shchapov.ru>
Date: Thu, 2 Jan 2025 22:54:19 +0500
Subject: [PATCH] Fix a bug when copying the fill from basic_specs

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
---
 include/fmt/format.h | 14 ++++++++++++--
 include/fmt/std.h    |  4 +---
 test/std-test.cc     |  3 +++
 test/xchar-test.cc   |  3 ++-
 4 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/include/fmt/format.h b/include/fmt/format.h
index d1b83d18..2fb85fef 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -3654,6 +3654,17 @@ void vformat_to(buffer<Char>& buf, basic_string_view<Char> fmt,
   parse_format_string(
       fmt, format_handler<Char>{parse_context<Char>(fmt), {out, args, loc}});
 }
+
+template <typename Char>
+void basic_specs_copy_fill(basic_specs& dst, const basic_specs& src) {
+  if (src.fill_size() == 1 && const_check(!std::is_same<Char, char>::value)) {
+    Char fill = src.fill_unit<Char>();
+    dst.set_fill(basic_string_view<Char>(&fill, 1));
+    return;
+  }
+  dst.set_fill(basic_string_view<char>(src.fill<char>(), src.fill_size()));
+}
+
 }  // namespace detail
 
 FMT_BEGIN_EXPORT
@@ -3960,8 +3971,7 @@ template <typename T, typename Char = char> struct nested_formatter {
     write(basic_appender<Char>(buf));
     auto specs = format_specs();
     specs.width = width_;
-    specs.set_fill(
-        basic_string_view<Char>(specs_.fill<Char>(), specs_.fill_size()));
+    detail::basic_specs_copy_fill<Char>(specs, specs_);
     specs.set_align(specs_.align());
     return detail::write<Char>(
         ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
diff --git a/include/fmt/std.h b/include/fmt/std.h
index cae14fb6..bc277d64 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -696,9 +696,7 @@ template <typename T, typename Char> struct formatter<std::complex<T>, Char> {
 
     auto outer_specs = format_specs();
     outer_specs.width = specs.width;
-    auto fill = specs.template fill<Char>();
-    if (fill)
-      outer_specs.set_fill(basic_string_view<Char>(fill, specs.fill_size()));
+    detail::basic_specs_copy_fill<Char>(outer_specs, specs);
     outer_specs.set_align(specs.align());
 
     specs.width = 0;
diff --git a/test/std-test.cc b/test/std-test.cc
index ab458ae8..2c57b3f6 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -91,6 +91,9 @@ TEST(std_test, complex) {
   EXPECT_EQ(fmt::format("{: }", std::complex<double>(1, 2.2)), "( 1+2.2i)");
   EXPECT_EQ(fmt::format("{: }", std::complex<double>(1, -2.2)), "( 1-2.2i)");
 
+  EXPECT_EQ(fmt::format("{:8}", std::complex<double>(1, 2)), "(1+2i)  ");
+  EXPECT_EQ(fmt::format("{:-<8}", std::complex<double>(1, 2)), "(1+2i)--");
+
   EXPECT_EQ(fmt::format("{:>20.2f}", std::complex<double>(1, 2.2)),
             "        (1.00+2.20i)");
   EXPECT_EQ(fmt::format("{:<20.2f}", std::complex<double>(1, 2.2)),
diff --git a/test/xchar-test.cc b/test/xchar-test.cc
index 9b02cd22..fd613e82 100644
--- a/test/xchar-test.cc
+++ b/test/xchar-test.cc
@@ -79,7 +79,7 @@ TEST(xchar_test, format) {
   EXPECT_THROW(fmt::format(fmt::runtime(L"{:*\x343E}"), 42), fmt::format_error);
   EXPECT_EQ(fmt::format(L"{}", true), L"true");
   EXPECT_EQ(fmt::format(L"{0}", L'a'), L"a");
-  EXPECT_EQ(fmt::format(L"Letter {}", L'\x40e'), L"Letter \x40e"); // Ў
+  EXPECT_EQ(fmt::format(L"Letter {}", L'\x40e'), L"Letter \x40e");  // Ў
   if (sizeof(wchar_t) == 4)
     EXPECT_EQ(fmt::format(fmt::runtime(L"{:𓀨>3}"), 42), L"𓀨42");
   EXPECT_EQ(fmt::format(L"{}c{}", L"ab", 1), L"abc1");
@@ -504,6 +504,7 @@ TEST(std_test_xchar, complex) {
   EXPECT_EQ(fmt::format(L"{:.2f}", std::complex<double>(1, 2)),
             L"(1.00+2.00i)");
   EXPECT_EQ(fmt::format(L"{:8}", std::complex<double>(1, 2)), L"(1+2i)  ");
+  EXPECT_EQ(fmt::format(L"{:-<8}", std::complex<double>(1, 2)), L"(1+2i)--");
 }
 
 TEST(std_test_xchar, optional) {