<xloctime>: Fix time_get::do_get to parse a literal %

stl/inc/xloctime

@@ -572,6 +572,14 @@ protected:
             }
             break;
 
+        case '%':
+            if (_First == _Last || _Ctype_fac.narrow(*_First) != '%') {
+                _State |= ios_base::failbit;
+            } else {
+                ++_First;
+            }
+            break;
+
         default:
             _State |= ios_base::failbit; // unknown specifier
             break;

tests/std/test.lst

@@ -280,6 +280,7 @@ tests\GH_005768_pow_accuracy
 tests\GH_005780_non_ascii_locales
 tests\GH_005800_stable_sort_large_alignment
 tests\GH_005968_headers_provide_begin_end
+tests\GH_006130_time_get_do_get_format
 tests\LWG2381_num_get_floating_point
 tests\LWG2510_tag_classes
 tests\LWG2597_complex_branch_cut

tests/std/tests/GH_006130_time_get_do_get_format/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_matrix.lst

tests/std/tests/GH_006130_time_get_do_get_format/test.cpp

@@ -0,0 +1,22 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <ctime>
+#include <iomanip>
+#include <sstream>
+
+int main() {
+    {
+        std::tm t{};
+        std::stringstream ss{"%"};
+        ss >> std::get_time(&t, "%%");
+        assert(!ss.fail() && ss.eof());
+    }
+    {
+        std::tm t{};
+        std::stringstream ss{"% "};
+        ss >> std::get_time(&t, "%%");
+        assert(!ss.fail() && ss.tellg() == 1);
+    }
+}