From 9f77586dbc1cf8e96047e45b3ccc283d26437239 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Fri, 14 Nov 2025 21:03:25 +0800
Subject: [PATCH 1/3] Implement LWG-4294

---
 stl/inc/bitset                                |  4 +-
 .../tests/Dev10_860410_bitset_ctors/test.cpp  | 95 +++++++++++++++++++
 2 files changed, 98 insertions(+), 1 deletion(-)

diff --git a/stl/inc/bitset b/stl/inc/bitset
index 13ed3252884..9b8a247a6d1 100644
--- a/stl/inc/bitset
+++ b/stl/inc/bitset
@@ -237,7 +237,9 @@ public:
         _Construct<_Traits>(_Str.data() + _Pos, _Count, _Elem0, _Elem1);
     }
 
-    template <class _Elem>
+    template <class _Elem, enable_if_t<conjunction_v<negation<is_array<_Elem>>, is_trivially_copyable<_Elem>,
+                                           is_standard_layout<_Elem>, is_trivially_default_constructible<_Elem>>,
+                               int> = 0>
     _CONSTEXPR23 explicit bitset(const _Elem* _Ntcts,
         typename basic_string<_Elem>::size_type _Count = basic_string<_Elem>::npos,
         _Elem _Elem0 = static_cast<_Elem>('0'), _Elem _Elem1 = static_cast<_Elem>('1')) {
diff --git a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
index 8121cab24df..0a283e3fd46 100644
--- a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
+++ b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
@@ -7,6 +7,7 @@
 #include <cstdlib>
 #include <stdexcept>
 #include <string>
+#include <type_traits>
 
 using namespace std;
 
@@ -31,6 +32,100 @@ namespace lwg_4140 {
     }
 } // namespace lwg_4140
 
+// Also test LWG-4294 "bitset(const CharT*) constructor needs to be constrained".
+
+template <size_t Len, class Elem, bool Expected>
+void test_ntcts_constructibility_single() { // COMPILE-ONLY
+    STATIC_ASSERT(is_constructible_v<bitset<Len>, Elem*> == Expected);
+    STATIC_ASSERT(is_constructible_v<bitset<Len>, const Elem*> == Expected);
+    // the constructor is explicit
+    STATIC_ASSERT(!is_convertible_v<Elem*, bitset<Len>>);
+    STATIC_ASSERT(!is_convertible_v<const Elem*, bitset<Len>>);
+}
+
+template <class Elem, bool Expected>
+void test_ntcts_constructibility_for_lengths() { // COMPILE-ONLY
+    test_ntcts_constructibility_single<0, Elem, Expected>();
+    test_ntcts_constructibility_single<1, Elem, Expected>();
+    test_ntcts_constructibility_single<8, Elem, Expected>();
+    test_ntcts_constructibility_single<16, Elem, Expected>();
+    test_ntcts_constructibility_single<32, Elem, Expected>();
+    test_ntcts_constructibility_single<48, Elem, Expected>();
+    test_ntcts_constructibility_single<64, Elem, Expected>();
+    test_ntcts_constructibility_single<96, Elem, Expected>();
+}
+
+void test_ntcts_constructibility() { // COMPILE-ONLY
+    // test encoded character types (expected usages)
+    test_ntcts_constructibility_for_lengths<char, true>();
+#ifdef __cpp_char8_t
+    test_ntcts_constructibility_for_lengths<char8_t, true>();
+#endif // __cpp_char8_t
+    test_ntcts_constructibility_for_lengths<char16_t, true>();
+    test_ntcts_constructibility_for_lengths<char32_t, true>();
+    test_ntcts_constructibility_for_lengths<wchar_t, true>();
+
+    enum unscoped_enum {};
+    enum class scoped_enum {};
+
+    struct pod_class {
+        int n1;
+    };
+    struct missing_trivial_default_ctor {
+        int n2 = 42;
+    };
+    struct missing_standard_layout : pod_class {
+        int n3;
+    };
+    struct missing_trivially_copyable {
+        missing_trivially_copyable()                                             = default;
+        missing_trivially_copyable(const missing_trivially_copyable&)            = default;
+        missing_trivially_copyable(missing_trivially_copyable&&)                 = default;
+        missing_trivially_copyable& operator=(const missing_trivially_copyable&) = default;
+        constexpr missing_trivially_copyable& operator=(missing_trivially_copyable&&) noexcept {
+            return *this;
+        }
+        ~missing_trivially_copyable() = default;
+    };
+
+    // test scalar types
+    test_ntcts_constructibility_for_lengths<int, true>();
+    test_ntcts_constructibility_for_lengths<char*, true>();
+    test_ntcts_constructibility_for_lengths<void (*)(), true>();
+    test_ntcts_constructibility_for_lengths<unscoped_enum, true>();
+    test_ntcts_constructibility_for_lengths<scoped_enum, true>();
+    test_ntcts_constructibility_for_lengths<int missing_trivial_default_ctor::*, true>();
+    test_ntcts_constructibility_for_lengths<void (missing_standard_layout::*)() const&, true>();
+
+    // test POD array types
+    test_ntcts_constructibility_for_lengths<char[1], false>();
+    test_ntcts_constructibility_for_lengths<char[1][2], false>();
+#ifdef __cpp_char8_t
+    test_ntcts_constructibility_for_lengths<char8_t[2], false>();
+    test_ntcts_constructibility_for_lengths<char8_t[2][4], false>();
+#endif // __cpp_char8_t
+    test_ntcts_constructibility_for_lengths<char16_t[3], false>();
+    test_ntcts_constructibility_for_lengths<char16_t[3][6], false>();
+    test_ntcts_constructibility_for_lengths<char32_t[4], false>();
+    test_ntcts_constructibility_for_lengths<char32_t[4][8], false>();
+    test_ntcts_constructibility_for_lengths<wchar_t[5], false>();
+    test_ntcts_constructibility_for_lengths<wchar_t[5][10], false>();
+    test_ntcts_constructibility_for_lengths<int[6], false>();
+    test_ntcts_constructibility_for_lengths<int[6][12][3], false>();
+    test_ntcts_constructibility_for_lengths<char* [7], false>();
+    test_ntcts_constructibility_for_lengths<char* [7][1][2][14], false>();
+
+    // test class types
+    test_ntcts_constructibility_for_lengths<pod_class, true>();
+    test_ntcts_constructibility_for_lengths<missing_trivial_default_ctor, false>();
+    test_ntcts_constructibility_for_lengths<missing_standard_layout, false>();
+    test_ntcts_constructibility_for_lengths<missing_trivially_copyable, false>();
+
+    // test worse class types
+    test_ntcts_constructibility_for_lengths<string, false>();
+    test_ntcts_constructibility_for_lengths<invalid_argument, false>();
+}
+
 const char parsedStr[] = "1000110111110011110111111111111111010111110111100101010100001001"
                          "1111111111111111111111111111111111111111111111111111111111111111"
                          "0111111111111111111111111111111111111111111111111111111111111111"

From 847fe01d2ed99341b7bb7c09b0e73fe27a79e2fc Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Fri, 14 Nov 2025 22:34:04 +0800
Subject: [PATCH 2/3] Fix test cases

---
 tests/std/tests/Dev10_860410_bitset_ctors/test.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
index 0a283e3fd46..68fabe95b36 100644
--- a/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
+++ b/tests/std/tests/Dev10_860410_bitset_ctors/test.cpp
@@ -36,8 +36,8 @@ namespace lwg_4140 {
 
 template <size_t Len, class Elem, bool Expected>
 void test_ntcts_constructibility_single() { // COMPILE-ONLY
-    STATIC_ASSERT(is_constructible_v<bitset<Len>, Elem*> == Expected);
-    STATIC_ASSERT(is_constructible_v<bitset<Len>, const Elem*> == Expected);
+    STATIC_ASSERT(is_constructible_v<bitset<Len>, Elem*, size_t, Elem, Elem> == Expected);
+    STATIC_ASSERT(is_constructible_v<bitset<Len>, const Elem*, size_t, Elem, Elem> == Expected);
     // the constructor is explicit
     STATIC_ASSERT(!is_convertible_v<Elem*, bitset<Len>>);
     STATIC_ASSERT(!is_convertible_v<const Elem*, bitset<Len>>);

From 6658d4d28df65853037d0f7c20c159a0040d305b Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Sat, 15 Nov 2025 07:42:23 +0800
Subject: [PATCH 3/3] Unblock one libcxx test

---
 tests/libcxx/expected_results.txt | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index 343abccc27a..329cbb8881f 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -77,9 +77,6 @@ std/input.output/iostreams.base/ios.base/ios.base.storage/pword.pass.cpp SKIPPED
 # LWG-3197 "std::prev should not require BidirectionalIterator" (New)
 std/iterators/iterator.primitives/iterator.operations/prev.pass.cpp FAIL
 
-# Testing nonstandard behavior
-std/utilities/template.bitset/bitset.cons/string_ctor.pass.cpp FAIL
-
 # Tests with undefined behavior under N4842 [basic.start.term]/6 (detached threads)
 std/thread/futures/futures.task/futures.task.members/dtor.pass.cpp SKIPPED
 std/thread/futures/futures.unique_future/wait_until.pass.cpp SKIPPED