From f262bb350ec2d1d5909e264e3e39193eaa2aa522 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Thu, 18 Jan 2024 08:54:39 +0700
Subject: [PATCH 1/2] fix formatting floating-point values without type and
 precision provided

---
 stl/inc/format                                         | 10 +++++++++-
 .../tests/P0645R10_text_formatting_formatting/test.cpp |  9 +++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/stl/inc/format b/stl/inc/format
index b0b97ca0575..622bcbca5f8 100644
--- a/stl/inc/format
+++ b/stl/inc/format
@@ -2967,6 +2967,7 @@ _NODISCARD _OutputIt _Fmt_write(
     auto _Format    = chars_format::general;
     auto _Exponent  = 'e';
     auto _Precision = _Specs._Precision;
+    auto _None_Type = false;
 
     switch (_Specs._Type) {
     case 'A':
@@ -3003,6 +3004,9 @@ _NODISCARD _OutputIt _Fmt_write(
         }
         _Format = chars_format::general;
         break;
+    default:
+        _None_Type = true;
+        break;
     }
 
     // Consider the powers of 2 in decimal:
@@ -3043,7 +3047,11 @@ _NODISCARD _OutputIt _Fmt_write(
         _Result.ptr += 3;
     } else {
         if (_Precision == -1) {
-            _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value, _Format);
+            if (_None_Type) {
+                _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value);
+            } else {
+                _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value, _Format);
+            }
         } else {
             _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value, _Format, _Precision);
         }
diff --git a/tests/std/tests/P0645R10_text_formatting_formatting/test.cpp b/tests/std/tests/P0645R10_text_formatting_formatting/test.cpp
index 7dea640f249..f516e4735e7 100644
--- a/tests/std/tests/P0645R10_text_formatting_formatting/test.cpp
+++ b/tests/std/tests/P0645R10_text_formatting_formatting/test.cpp
@@ -1506,6 +1506,12 @@ constexpr bool test_format_string() {
     return true;
 }
 
+// Also test GH-4319: incorrect output for some floating-point values
+template <class charT>
+void test_gh_4319() {
+    assert(format(STR("{:}"), 12345678.0) == STR("12345678"));
+}
+
 void test() {
     test_simple_formatting<char>();
     test_simple_formatting<wchar_t>();
@@ -1582,6 +1588,9 @@ void test() {
     test_localized_char<char, char>();
     test_localized_char<wchar_t, char>();
     test_localized_char<wchar_t, wchar_t>();
+
+    test_gh_4319<char>();
+    test_gh_4319<wchar_t>();
 }
 
 int main() {

From 3400d621ada9299ee89118a0fb977d092762e3af Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Thu, 18 Jan 2024 09:09:34 +0700
Subject: [PATCH 2/2] _None_Type => _None_type

---
 stl/inc/format | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/stl/inc/format b/stl/inc/format
index 622bcbca5f8..d5e6de99b86 100644
--- a/stl/inc/format
+++ b/stl/inc/format
@@ -2967,7 +2967,7 @@ _NODISCARD _OutputIt _Fmt_write(
     auto _Format    = chars_format::general;
     auto _Exponent  = 'e';
     auto _Precision = _Specs._Precision;
-    auto _None_Type = false;
+    auto _None_type = false;
 
     switch (_Specs._Type) {
     case 'A':
@@ -3005,7 +3005,7 @@ _NODISCARD _OutputIt _Fmt_write(
         _Format = chars_format::general;
         break;
     default:
-        _None_Type = true;
+        _None_type = true;
         break;
     }
 
@@ -3047,7 +3047,7 @@ _NODISCARD _OutputIt _Fmt_write(
         _Result.ptr += 3;
     } else {
         if (_Precision == -1) {
-            if (_None_Type) {
+            if (_None_type) {
                 _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value);
             } else {
                 _Result = _STD to_chars(_Buffer, _STD end(_Buffer), _Value, _Format);