[libcxx-commits] [libcxx] [libc++] Tweak how we check constraints on shared_ptr(nullptr_t) (PR #94996)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne created https://github.com/llvm/llvm-project/pull/94996

This avoids breaking code that should arguably be valid but technically isn't after enforcing the constraints on shared_ptr's constructors. A new LWG issue was filed to fix this in the Standard.

This patch applies the expected resolution of this issue to avoid flip-flopping users whose code should always be considered valid.

See #93071 for more context.

>From 0241c4c355cc836944bfc5d03a1a4b7e84487544 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Mon, 10 Jun 2024 11:05:28 -0400
Subject: [PATCH] [libc++] Tweak how we check constraints on
 shared_ptr(nullptr_t)

This avoids breaking code that should arguably be valid but technically
isn't after enforcing the constraints on shared_ptr's constructors. A
new LWG issue was filed to fix this in the Standard.

This patch applies the expected resolution of this issue to avoid
flip-flopping users whose code should always be considered valid.

See #93071 for more context.
---
 libcxx/include/__memory/shared_ptr.h                        | 2 +-
 .../util.smartptr.shared.const/nullptr_t_deleter.pass.cpp   | 5 ++---
 .../nullptr_t_deleter_allocator.pass.cpp                    | 5 ++---
 .../util.smartptr.shared.const/pointer_deleter.pass.cpp     | 6 ++++++
 .../pointer_deleter_allocator.pass.cpp                      | 6 ++++++
 5 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/libcxx/include/__memory/shared_ptr.h b/libcxx/include/__memory/shared_ptr.h
index 00db96185be7c..7b5002cb95d32 100644
--- a/libcxx/include/__memory/shared_ptr.h
+++ b/libcxx/include/__memory/shared_ptr.h
@@ -404,7 +404,7 @@ struct __shared_ptr_deleter_ctor_reqs {
 };
 
 template <class _Dp, class _Tp>
-using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
+using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, _Tp*> >;
 
 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter.pass.cpp
index 13340ed5294c0..9c93f2e361d24 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter.pass.cpp
@@ -33,16 +33,15 @@ int A::count = 0;
 // https://cplusplus.github.io/LWG/issue3233
 static_assert( std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, test_deleter<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, bad_deleter>::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_nullptr_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_move_deleter>::value, "");
 
 #if TEST_STD_VER >= 17
-static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int> >::value, "");
+static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int[]> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, bad_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_nullptr_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_move_deleter>::value, "");
 
-static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int> >::value, "");
+static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int[5]> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, bad_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_nullptr_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_move_deleter>::value, "");
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter_allocator.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter_allocator.pass.cpp
index 53ca6fb5b234d..f95b9e68dad01 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter_allocator.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter_allocator.pass.cpp
@@ -34,16 +34,15 @@ int A::count = 0;
 // https://cplusplus.github.io/LWG/issue3233
 static_assert( std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");
 
 #if TEST_STD_VER >= 17
-static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
+static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int[]>, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");
 
-static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
+static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int[5]>, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp
index 562acf56d96fe..bcae00ef2e031 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp
@@ -115,6 +115,12 @@ int main(int, char**)
     }
 #endif // TEST_STD_VER >= 11
 
+    {
+        // See https://github.com/llvm/llvm-project/pull/93071#issuecomment-2158494851
+        auto deleter = [](auto pointer) { delete pointer; };
+        std::shared_ptr<int> p(new int, deleter);
+    }
+
   test_function_type();
   return 0;
 }
diff --git a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter_allocator.pass.cpp b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter_allocator.pass.cpp
index 9dffbcdd59a73..66adff62b0707 100644
--- a/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter_allocator.pass.cpp
+++ b/libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter_allocator.pass.cpp
@@ -165,5 +165,11 @@ int main(int, char**)
                                              test_allocator<Derived[4]> >::value, "");
     }
 
+    {
+        // See https://github.com/llvm/llvm-project/pull/93071#issuecomment-2158494851
+        auto deleter = [](auto pointer) { delete pointer; };
+        std::shared_ptr<int> p(new int, deleter, std::allocator<int>());
+    }
+
   return 0;
 }