From 5ac862362900773fb95a8c9ab58fe49721e8cd92 Mon Sep 17 00:00:00 2001
From: Yuanhong Zhao <yuanhongzhao87@gmail.com>
Date: Fri, 2 Jul 2021 23:36:43 -0700
Subject: [PATCH 1/4] LWG-3536: leave duration unchanged on failed parse

---
 stl/inc/chrono                                              | 1 -
 .../std/tests/P0355R7_calendars_and_time_zones_io/test.cpp  | 6 ++++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/stl/inc/chrono b/stl/inc/chrono
index 09c8dad9aee..3c289f4d781 100644
--- a/stl/inc/chrono
+++ b/stl/inc/chrono
@@ -4137,7 +4137,6 @@ namespace chrono {
         _NODISCARD bool _Make_duration(duration<_Rep, _Period>& _Duration_result) {
             const bool _Consistent = _Calculate_hour24();
             if (_Consistent) {
-                _Duration_result = duration<_Rep, _Period>::zero(); // TRANSITION: LWG-3536 & GH-1740
                 return _Apply_duration_fields<_Parse_tp_or_duration::_Duration>(_Duration_result);
             }
 
diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
index 947ec200f59..7c71419cc7a 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
@@ -262,6 +262,12 @@ void parse_seconds() {
 
     fail_parse("1.2 1.3", "%S %S", time_ms);
     fail_parse("1.2 2.2", "%S %S", time_ms);
+
+    // LWG-3536, failed parse leaves duration unmodified.
+    minutes mm{20};
+    istringstream iss{"2:2:20"};
+    iss >> parse(string{"%H:%M:%S"}, mm);
+    assert(iss.fail() && mm == 20min);
 }
 
 void parse_minutes() {

From 1abd9cec59584b7cbf7dad08ab0b2c2f4fb9e2aa Mon Sep 17 00:00:00 2001
From: Yuanhong Zhao <yuanhongzhao87@gmail.com>
Date: Wed, 4 Aug 2021 14:20:11 -0700
Subject: [PATCH 2/4] code review feedback

---
 .../test.cpp                                  | 29 +++++++++++++++----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
index 7c71419cc7a..288eb5f96d2 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
@@ -221,6 +221,29 @@ void test_limits(const char* flag, const IntType min, const IntType max) {
     assert(value == TimeType{max});
 }
 
+void test_lwg_3536() {
+    // LWG-3536, "Should chrono::from_stream() assign zero to duration for failure?"
+    minutes mm{20};
+
+    {
+        istringstream iss{"2:2:20"};
+        iss >> parse(string{"%H:%M:%S"}, mm);
+        assert(iss.fail() && mm == 20min);
+    }
+
+    {
+        istringstream iss{"June"};
+        iss >> parse(string{"%B"}, mm);
+        assert(iss.fail() && mm == 20min);
+    }
+
+    {
+        istringstream iss{""};
+        iss >> parse(string{"%B"}, mm);
+        assert(iss.fail() && mm == 20min);
+    }
+}
+
 void parse_seconds() {
     seconds time;
     test_parse("1", "%S", time);
@@ -263,11 +286,7 @@ void parse_seconds() {
     fail_parse("1.2 1.3", "%S %S", time_ms);
     fail_parse("1.2 2.2", "%S %S", time_ms);
 
-    // LWG-3536, failed parse leaves duration unmodified.
-    minutes mm{20};
-    istringstream iss{"2:2:20"};
-    iss >> parse(string{"%H:%M:%S"}, mm);
-    assert(iss.fail() && mm == 20min);
+    test_lwg_3536();
 }
 
 void parse_minutes() {

From 5d552790a2b1b78daa1a6267b3e259faa7f4ca76 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@nuwen.net>
Date: Fri, 13 Aug 2021 16:28:36 -0700
Subject: [PATCH 3/4] Parse "2:2:30" so 20 can be a unique value.

---
 tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
index 288eb5f96d2..a993214de0c 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
@@ -226,7 +226,7 @@ void test_lwg_3536() {
     minutes mm{20};
 
     {
-        istringstream iss{"2:2:20"};
+        istringstream iss{"2:2:30"};
         iss >> parse(string{"%H:%M:%S"}, mm);
         assert(iss.fail() && mm == 20min);
     }

From 32d30dedae6b72b6760a2220505e1e67c1b5d45e Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@nuwen.net>
Date: Fri, 13 Aug 2021 16:44:08 -0700
Subject: [PATCH 4/4] Call test_lwg_3536() in test_parse().

---
 tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
index a993214de0c..373f7da3536 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
@@ -285,8 +285,6 @@ void parse_seconds() {
 
     fail_parse("1.2 1.3", "%S %S", time_ms);
     fail_parse("1.2 2.2", "%S %S", time_ms);
-
-    test_lwg_3536();
 }
 
 void parse_minutes() {
@@ -1207,6 +1205,7 @@ void parse_wchar() {
 }
 
 void test_parse() {
+    test_lwg_3536();
     parse_seconds();
     parse_minutes();
     parse_hours();