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Re: [PATCH] PR libstdc++/87704 fix unique_ptr(nullptr_t) constructors


On 23/10/18 14:10 +0100, Jonathan Wakely wrote:
Using a delegating constructor to implement these constructors means
that they instantiate the destructor, which requires the element_type to
be complete. In C++11 and C++14 they were specified to be delegating,
but that was changed as part of LWG 2801 so in C++17 they don't require
a complete type (as was intended all along).

	PR libstdc++/87704
	* include/bits/unique_ptr.h (unique_ptr::unique_ptr(nullptr_t)): Do
	not delegate to default constructor.
	(unique_ptr<T[], D>::unique_ptr(nullptr_t)): Likewise.
	* testsuite/20_util/unique_ptr/cons/incomplete.cc: New test.

Tested powerpc64le-linux, committed to trunk. Backports to follow.

This is the backport for gcc-6-branch. It's slightly different,
because on that branch we make null deleters ill-formed via
static_assert, instead of disabling the constructor via SFINAE. If
the unique_ptr(nullptr_t) constructors don't delegate to the default
constructor they need to duplicate the assertion from the default
constructor.

Tested x86_64-linux.


commit c1a59bedb89bde9f7e45b187409186b2f9763637
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Tue Oct 23 15:55:05 2018 +0000

    PR libstdc++/87704 fix unique_ptr(nullptr_t) constructors
    
    Using a delegating constructor to implement these constructors means
    that they instantiate the destructor, which requires the element_type to
    be complete. In C++11 and C++14 they were specified to be delegating,
    but that was changed as part of LWG 2801 so in C++17 they don't require
    a complete type (as was intended all along).
    
    Backport from mainline
    2018-10-23  Jonathan Wakely  <jwakely@redhat.com>
    
            PR libstdc++/87704
            * include/bits/unique_ptr.h (unique_ptr::unique_ptr(nullptr_t)): Do
            not delegate to default constructor.
            (unique_ptr<T[], D>::unique_ptr(nullptr_t)): Likewise.
            * testsuite/20_util/unique_ptr/cons/incomplete.cc: New test.

diff --git a/libstdc++-v3/include/bits/unique_ptr.h b/libstdc++-v3/include/bits/unique_ptr.h
index 8e302877f78..93c579788b6 100644
--- a/libstdc++-v3/include/bits/unique_ptr.h
+++ b/libstdc++-v3/include/bits/unique_ptr.h
@@ -201,7 +201,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		      "rvalue deleter bound to reference"); }
 
       /// Creates a unique_ptr that owns nothing.
-      constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
+      constexpr unique_ptr(nullptr_t) noexcept : _M_t()
+      { static_assert(!is_pointer<deleter_type>::value,
+		      "constructed with null function pointer deleter"); }
 
       // Move constructors.
 
@@ -491,7 +493,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _M_t(__u.release(), std::forward<deleter_type>(__u.get_deleter())) { }
 
       /// Creates a unique_ptr that owns nothing.
-      constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
+      constexpr unique_ptr(nullptr_t) noexcept : _M_t()
+      { static_assert(!is_pointer<deleter_type>::value,
+		      "constructed with null function pointer deleter"); }
 
       template<typename _Up, typename _Ep,
 	       typename = _Require<__safe_conversion_up<_Up, _Ep>>>
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/assign/48635_neg.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/assign/48635_neg.cc
index 785f9ad4cfd..e64b4535345 100644
--- a/libstdc++-v3/testsuite/20_util/unique_ptr/assign/48635_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/assign/48635_neg.cc
@@ -43,10 +43,10 @@ void f()
   std::unique_ptr<int, D&> ud(nullptr, d);
   ub = std::move(ud); // { dg-error "no match" }
   ub2 = ud; // { dg-error "no match" }
-// { dg-error "no type" "" { target *-*-* } 272 }
+// { dg-error "no type" "" { target *-*-* } 274 }
 
   std::unique_ptr<int[], B&> uba(nullptr, b);
   std::unique_ptr<int[], D&> uda(nullptr, d);
   uba = std::move(uda); // { dg-error "no match" }
-// { dg-error "no type" "" { target *-*-* } 540 }
+// { dg-error "no type" "" { target *-*-* } 544 }
 }
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/cons/cv_qual_neg.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/cons/cv_qual_neg.cc
index 285a0b994c9..9b8cba45a57 100644
--- a/libstdc++-v3/testsuite/20_util/unique_ptr/cons/cv_qual_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/cons/cv_qual_neg.cc
@@ -40,7 +40,7 @@ test07()
   std::unique_ptr<const A[]> cA3(p); // { dg-error "no matching function" }
   std::unique_ptr<volatile A[]> vA3(p); // { dg-error "no matching function" }
   std::unique_ptr<const volatile A[]> cvA3(p); // { dg-error "no matching function" }
-  // { dg-error "no type" "" { target *-*-* } 448 }
+  // { dg-error "no type" "" { target *-*-* } 450 }
 }
 
 template<typename T>
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/cons/incomplete.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/cons/incomplete.cc
new file mode 100644
index 00000000000..1a8f28838a1
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/cons/incomplete.cc
@@ -0,0 +1,32 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <memory>
+
+struct Incomplete;
+
+void f(void** p)
+{
+  ::new (p[0]) std::unique_ptr<Incomplete>();
+  ::new (p[1]) std::unique_ptr<Incomplete[]>();
+
+  // PR libstdc++/87704
+  ::new (p[2]) std::unique_ptr<Incomplete>(nullptr);
+  ::new (p[3]) std::unique_ptr<Incomplete[]>(nullptr);
+}

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