Implement LWG-3598 system_category().default_error_condition(0)

stl/inc/system_error

@@ -501,7 +501,12 @@ public:
     }
 
     _NODISCARD string message(int _Errcode) const override {
-        return _Syserror_map(_Errcode);
+        // TRANSITION, GH-2561, move the logic to syserror.cpp
+        if (_Errcode == 0) {
+            return "success";
+        } else {
+            return _Syserror_map(_Errcode);
+        }
     }
 };
 
@@ -544,12 +549,16 @@ public:
     }
 
     _NODISCARD error_condition default_error_condition(int _Errval) const noexcept override {
-        // make error_condition for error code (generic if possible)
-        const int _Posv = _Winerror_map(_Errval);
-        if (_Posv == 0) {
-            return error_condition(_Errval, _STD system_category());
+        if (_Errval == 0) {
+            return error_condition(0, _STD generic_category());
         } else {
-            return error_condition(_Posv, _STD generic_category());
+            // make error_condition for error code (generic if possible)
+            const int _Posv = _Winerror_map(_Errval);
+            if (_Posv == 0) {
+                return error_condition(_Errval, _STD system_category());
+            } else {
+                return error_condition(_Posv, _STD generic_category());
+            }
         }
     }
 };

tests/std/tests/Dev11_0493504_error_category_lifetime/test.cpp

@@ -28,6 +28,17 @@ struct Global {
 
 Global global;
 
+// Also test LWG-3598: system_category().default_error_condition(0) has a generic category.
+void test_lwg_3598() {
+    error_condition cond = system_category().default_error_condition(0);
+
+    assert(cond.category() == generic_category());
+    assert(cond.message() == "success");
+    assert(cond.value() == 0);
+
+    assert(error_code() == error_condition());
+}
+
 int main() {
     // Also test DevDiv-781294 "<system_error>: Visual C++ 2013 RC system_category().equivalent function does not work".
     const error_code code(ERROR_NOT_ENOUGH_MEMORY, system_category());
@@ -44,6 +55,8 @@ int main() {
     // Also test VSO-649432 <system_error> system_category().message() ends with extra newlines
     const auto msg = code.message();
     assert(!msg.empty() && msg.back() != '\0' && !isspace(static_cast<unsigned char>(msg.back())));
+
+    test_lwg_3598();
 }
 
 

tests/tr1/tests/system_error/test.cpp

@@ -133,7 +133,7 @@ void test_main() { // run tests
         CHECK(!(ec1 < ec1));
 
         STD error_condition ec0x, ec1x(ERR too_many_links);
-        CHECK(ec0 != ec0x);
+        CHECK(ec0 == ec0x);
         CHECK(ec0 != ec1x);
         CHECK(!STD is_error_code_enum<ERR_ENUM>::value);
         CHECK(ec1 == STD make_error_code(ERR too_many_links));
@@ -167,7 +167,7 @@ void test_main() { // run tests
         CHECK(!(ec1 < ec1));
 
         STD error_code ec0x, ec1x = STD make_error_code(ERR too_many_links);
-        CHECK(ec0 != ec0x);
+        CHECK(ec0 == ec0x);
         CHECK(ec0 != ec1x);
         CHECK(STD is_error_condition_enum<ERR_ENUM>::value);
         CHECK(ec1 == STD make_error_condition(ERR too_many_links));