Fix field width handling in enum stream output

include/magic_enum/magic_enum_iostream.hpp

@@ -37,10 +37,31 @@
 
 #ifndef MAGIC_ENUM_USE_STD_MODULE
 #  include <iosfwd>
+#  include <string>
+#  include <string_view>
 #endif
 
 namespace magic_enum {
 
+namespace detail {
+
+// Formatted insertion, so width, fill and adjustfield apply to the name as a whole.
+template <typename Char, typename Traits>
+std::basic_ostream<Char, Traits>& write_name(std::basic_ostream<Char, Traits>& os, string_view name) {
+  if constexpr (std::is_same_v<Char, char_type>) {
+    return os << std::basic_string_view<Char, Traits>{name.data(), name.size()};
+  } else {
+    std::basic_string<Char, Traits> s;
+    s.reserve(name.size());
+    for (const auto c : name) {
+      s.push_back(static_cast<Char>(c));
+    }
+    return os << s;
+  }
+}
+
+} // namespace magic_enum::detail
+
 namespace ostream_operators {
 
 template <typename Char, typename Traits, typename E, detail::enable_if_t<E, int> = 0>
@@ -51,17 +72,11 @@ std::basic_ostream<Char, Traits>& operator<<(std::basic_ostream<Char, Traits>& o
   if constexpr (detail::supported<D>::value) {
     if constexpr (detail::subtype_v<D> == detail::enum_subtype::flags) {
       if (const auto name = enum_flags_name<D>(value); !name.empty()) {
-        for (std::size_t i = 0; i < name.size(); ++i) {
-          os.put(name.data()[i]);
-        }
-        return os;
+        return detail::write_name(os, string_view{name.data(), name.size()});
       }
     } else {
       if (const auto name = enum_name<D>(value); !name.empty()) {
-        for (std::size_t i = 0; i < name.size(); ++i) {
-          os.put(name.data()[i]);
-        }
-        return os;
+        return detail::write_name(os, name);
       }
     }
   }

test/test.cpp

@@ -22,6 +22,7 @@
 
 #include <array>
 #include <cctype>
+#include <iomanip>
 #include <memory>
 #include <string>
 #include <string_view>
@@ -1250,6 +1251,27 @@ TEST_CASE("ostream_operators") {
 #endif
   }
 
+  SUBCASE("field width applies to the name") {
+    using namespace magic_enum::ostream_operators;
+
+    std::ostringstream named;
+    named << std::setfill('_') << std::setw(6) << Color::GREEN << '|' << std::left << std::setw(6) << Color::BLUE << '|' << Color::BLUE << '|';
+    REQUIRE(named.str() == "_GREEN|BLUE__|BLUE|");
+
+    std::ostringstream fallback;
+    fallback << std::setfill('_') << std::setw(6) << static_cast<Color>(0) << '|' << std::setw(6) << std::make_optional(Color::BLUE) << '|';
+    REQUIRE(fallback.str() == "_____0|__BLUE|");
+
+    std::basic_ostringstream<char, CustomCharTraits<char>> custom;
+    custom << std::setfill('_') << std::setw(6) << Color::BLUE << '|';
+    const auto result = custom.str();
+    REQUIRE(std::string(result.data(), result.size()) == "__BLUE|");
+
+    std::wostringstream wide;
+    wide << std::setfill(L'_') << std::setw(6) << Color::BLUE << L'|';
+    REQUIRE(wide.str() == L"__BLUE|");
+  }
+
   SUBCASE("short underlying type formatting") {
     using namespace magic_enum::ostream_operators;
     enum class Small : short { Named = 1 };

test/test_aliases.cpp

@@ -10,6 +10,7 @@
 
 #include "test_helpers.hpp"
 
+#include <iomanip>
 #include <sstream>
 
 using namespace magic_enum;
@@ -145,3 +146,15 @@ TEST_CASE("string containers") {
   stream << colors;
   REQUIRE(stream.str() == "RED|BLUE");
 }
+
+TEST_CASE("ostream_operators") {
+  using namespace magic_enum::ostream_operators;
+
+  std::ostringstream narrow;
+  narrow << std::setfill('_') << std::setw(10) << (Color::RED | Color::BLUE) << '|';
+  REQUIRE(narrow.str() == "__RED|BLUE|");
+
+  std::wostringstream wide;
+  wide << std::setfill(L'_') << std::setw(10) << (Color::RED | Color::BLUE) << L'|';
+  REQUIRE(wide.str() == L"__RED|BLUE|");
+}

test/test_flags.cpp

@@ -15,6 +15,7 @@
 
 #include <array>
 #include <cctype>
+#include <iomanip>
 #include <string>
 #include <string_view>
 
@@ -780,6 +781,13 @@ TEST_CASE("ostream_operators") {
     REQUIRE(stream.str() == "false");
   }
 
+  SUBCASE("field width applies to the whole name") {
+    using namespace magic_enum::ostream_operators;
+    std::ostringstream stream;
+    stream << std::setfill('_') << std::setw(10) << (Color::BLUE | Color::RED) << '|' << std::left << std::setw(10) << (Color::BLUE | Color::RED) << '|';
+    REQUIRE(stream.str() == "__RED|BLUE|RED|BLUE__|");
+  }
+
   require_ostream(std::make_optional(Color::RED), "RED");
   require_ostream(Color::GREEN, "GREEN");
   require_ostream(Color::BLUE, "BLUE");

test/test_wchar_t.cpp

@@ -17,6 +17,7 @@
 
 #include <array>
 #include <cctype>
+#include <iomanip>
 #include <sstream>
 
 enum class Color { RED = -12, GREEN = 7, BLUE = 15 };
@@ -150,6 +151,18 @@ TEST_CASE("wstring_view lifetime and null termination") {
 }
 
 TEST_CASE("ostream_operators") {
+  SUBCASE("field width applies to the name") {
+    using namespace magic_enum::ostream_operators;
+
+    std::wostringstream wide;
+    wide << std::setfill(L'_') << std::setw(6) << Color::RED << L'|';
+    REQUIRE(wide.str() == L"___red|");
+
+    std::ostringstream narrow;
+    narrow << std::setfill('_') << std::setw(6) << Color::RED << '|';
+    REQUIRE(narrow.str() == "___red|");
+  }
+
   require_ostream(std::make_optional(Color::RED), L"red");
   require_ostream(Color::GREEN, L"GREEN");
   require_ostream(Color::BLUE, L"BLUE");