Make std::enable_shared_from_this cope with ambiguity

* include/backward/auto_ptr.h (__shared_ptr(auto_ptr&&)): Call
	_M_enable_shared_from_this_with instead of
	__enable_shared_from_this_helper.
	* include/bits/shared_ptr.h (__enable_shared_from_this_helper):
	Remove overload for std::enable_shared_from_this..
	(__enable_shared_from_this_base): Define friend function to select a
	std::enable_shared_from_this base class.
	* include/bits/shared_ptr_base.h (__enable_shared_from_this_helper):
	Remove all overloads.
	(__shared_ptr): Change all relevant constructors to call
	_M_enable_shared_from_this_with instead of
	__enable_shared_from_this_helper.
	(__shared_ptr::__efst_base_t, __shared_ptr::__has_efst_base): Helpers
	to detect accessible and unambiguous enable_shared_from_this bases.
	(__shared_ptr::_M_enable_shared_from_this_with): New function to
	replace __enable_shared_from_this_helper overloads.
	(__enable_shared_from_this_helper): Remove overload for
	std::__enable_shared_from_this.
	(__enable_shared_from_this_base): Define friend function to select a
	std::__enable_shared_from_this base class.
	* include/experimental/bits/shared_ptr.h (experimental::shared_ptr):
	Change relevant constructors to call _M_enable_shared_from_this_with.
	(experimental::shared_ptr::__efst_base_t)
	(experimental::shared_ptr::__has_efst_base): Helpers to detect
	accessible and unambiguous enable_shared_from_this bases.
	(experimental::shared_ptr::_M_enable_shared_from_this_with): Define.
	(experimental::__enable_shared_from_this_helper): Remove overload for
	std::experimental::enable_shared_from_this.
	(experimental::__expt_enable_shared_from_this_base): Define friend
	function to select a std::experimental::enable_shared_from_this base.
	* testsuite/experimental/memory/shared_ptr/cons/
	enable_shared_from_this.cc: New test.
	* testsuite/experimental/memory/shared_ptr/cons/unique_ptr_ctor.cc:
	Adjust expected behaviour for shared_ptr<A[]>.

From-SVN: r241353

libstdc++-v3/ChangeLog

@@ -1,5 +1,40 @@
 2016-10-19  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/backward/auto_ptr.h (__shared_ptr(auto_ptr&&)): Call
+	_M_enable_shared_from_this_with instead of
+	__enable_shared_from_this_helper.
+	* include/bits/shared_ptr.h (__enable_shared_from_this_helper):
+	Remove overload for std::enable_shared_from_this..
+	(__enable_shared_from_this_base): Define friend function to select a
+	std::enable_shared_from_this base class.
+	* include/bits/shared_ptr_base.h (__enable_shared_from_this_helper):
+	Remove all overloads.
+	(__shared_ptr): Change all relevant constructors to call
+	_M_enable_shared_from_this_with instead of
+	__enable_shared_from_this_helper.
+	(__shared_ptr::__efst_base_t, __shared_ptr::__has_efst_base): Helpers
+	to detect accessible and unambiguous enable_shared_from_this bases.
+	(__shared_ptr::_M_enable_shared_from_this_with): New function to
+	replace __enable_shared_from_this_helper overloads.
+	(__enable_shared_from_this_helper): Remove overload for
+	std::__enable_shared_from_this.
+	(__enable_shared_from_this_base): Define friend function to select a
+	std::__enable_shared_from_this base class.
+	* include/experimental/bits/shared_ptr.h (experimental::shared_ptr):
+	Change relevant constructors to call _M_enable_shared_from_this_with.
+	(experimental::shared_ptr::__efst_base_t)
+	(experimental::shared_ptr::__has_efst_base): Helpers to detect
+	accessible and unambiguous enable_shared_from_this bases.
+	(experimental::shared_ptr::_M_enable_shared_from_this_with): Define.
+	(experimental::__enable_shared_from_this_helper): Remove overload for
+	std::experimental::enable_shared_from_this.
+	(experimental::__expt_enable_shared_from_this_base): Define friend
+	function to select a std::experimental::enable_shared_from_this base.
+	* testsuite/experimental/memory/shared_ptr/cons/
+	enable_shared_from_this.cc: New test.
+	* testsuite/experimental/memory/shared_ptr/cons/unique_ptr_ctor.cc:
+	Adjust expected behaviour for shared_ptr<A[]>.
+
 	* include/debug/vector (__gnu_debug::vector::emplace_back): Fix return
 	type.
 

libstdc++-v3/include/backward/auto_ptr.h

@@ -311,7 +311,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static_assert( sizeof(_Tp1) > 0, "incomplete type" );
       _Tp1* __tmp = __r.get();
       _M_refcount = __shared_count<_Lp>(std::move(__r));
-      __enable_shared_from_this_helper(_M_refcount, __tmp, __tmp);
+      _M_enable_shared_from_this_with(__tmp);
     }
 
   template<typename _Tp>

libstdc++-v3/include/bits/shared_ptr.h

@@ -607,25 +607,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
 	{ _M_weak_this._M_assign(__p, __n); }
 
-      template<typename _Tp1, typename _Tp2>
+      // Found by ADL when this is an associated class.
-	friend void
+      friend const enable_shared_from_this*
-	__enable_shared_from_this_helper(const __shared_count<>&,
+      __enable_shared_from_this_base(const __shared_count<>&,
-					 const enable_shared_from_this<_Tp1>*,
+				     const enable_shared_from_this* __p)
-					 const _Tp2*) noexcept;
+      { return __p; }
+
+      template<typename, _Lock_policy>
+	friend class __shared_ptr;
 
       mutable weak_ptr<_Tp>  _M_weak_this;
     };
 
-  template<typename _Tp1, typename _Tp2>
-    inline void
-    __enable_shared_from_this_helper(const __shared_count<>& __pn,
-				     const enable_shared_from_this<_Tp1>*
-				     __pe, const _Tp2* __px) noexcept
-    {
-      if (__pe != nullptr)
-	__pe->_M_weak_assign(const_cast<_Tp2*>(__px), __pn);
-    }
-
   /**
    *  @brief  Create an object that is owned by a shared_ptr.
    *  @param  __a     An allocator.

libstdc++-v3/include/bits/shared_ptr_base.h

@@ -847,28 +847,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  _M_pi = nullptr;
     }
 
-  // Support for enable_shared_from_this.
-
-  // Friend of __enable_shared_from_this.
-  template<_Lock_policy _Lp, typename _Tp1, typename _Tp2>
-    void
-    __enable_shared_from_this_helper(const __shared_count<_Lp>&,
-				     const __enable_shared_from_this<_Tp1,
-				     _Lp>*, const _Tp2*) noexcept;
-
-  // Friend of enable_shared_from_this.
-  template<typename _Tp1, typename _Tp2>
-    void
-    __enable_shared_from_this_helper(const __shared_count<>&,
-				     const enable_shared_from_this<_Tp1>*,
-				     const _Tp2*) noexcept;
-
-  template<_Lock_policy _Lp>
-    inline void
-    __enable_shared_from_this_helper(const __shared_count<_Lp>&, ...) noexcept
-    { }
-
-
   template<typename _Tp, _Lock_policy _Lp>
     class __shared_ptr
     {
@@ -898,7 +876,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 	  static_assert( !is_void<_Tp1>::value, "incomplete type" );
 	  static_assert( sizeof(_Tp1) > 0, "incomplete type" );
-	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	  _M_enable_shared_from_this_with(__p);
 	}
 
       template<typename _Tp1, typename _Deleter>
@@ -907,7 +885,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
-	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	  _M_enable_shared_from_this_with(__p);
 	}
 
       template<typename _Tp1, typename _Deleter, typename _Alloc>
@@ -916,7 +894,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 	  // TODO requires _Deleter CopyConstructible and __d(__p) well-formed
-	  __enable_shared_from_this_helper(_M_refcount, __p, __p);
+	  _M_enable_shared_from_this_with(__p);
 	}
 
       template<typename _Deleter>
@@ -978,7 +956,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
 	  auto __raw = _S_raw_ptr(__r.get());
 	  _M_refcount = __shared_count<_Lp>(std::move(__r));
-	  __enable_shared_from_this_helper(_M_refcount, __raw, __raw);
+	  _M_enable_shared_from_this_with(__raw);
 	}
 
 #if _GLIBCXX_USE_DEPRECATED
@@ -1114,7 +1092,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
 	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
 	  _M_ptr = static_cast<_Tp*>(__p);
-	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
+	  _M_enable_shared_from_this_with(_M_ptr);
 	}
 #else
       template<typename _Alloc>
@@ -1146,7 +1124,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  __shared_count<_Lp> __count(__ptr, __del, __del._M_alloc);
 	  _M_refcount._M_swap(__count);
 	  _M_ptr = __ptr;
-	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
+	  _M_enable_shared_from_this_with(_M_ptr);
 	}
 #endif
 
@@ -1166,6 +1144,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       friend class __weak_ptr<_Tp, _Lp>;
 
     private:
+
+      template<typename _Yp>
+	using __esft_base_t = decltype(__enable_shared_from_this_base(
+	      std::declval<const __shared_count<_Lp>&>(),
+	      std::declval<_Yp*>()));
+
+      // Detect an accessible and unambiguous enable_shared_from_this base.
+      template<typename _Yp, typename = void>
+	struct __has_esft_base
+	: false_type { };
+
+      template<typename _Yp>
+	struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
+	: true_type { };
+
+      template<typename _Yp>
+	typename enable_if<__has_esft_base<_Yp>::value>::type
+	_M_enable_shared_from_this_with(const _Yp* __p) noexcept
+	{
+	  if (auto __base = __enable_shared_from_this_base(_M_refcount, __p))
+	    __base->_M_weak_assign(const_cast<_Yp*>(__p), _M_refcount);
+	}
+
+      template<typename _Yp>
+	typename enable_if<!__has_esft_base<_Yp>::value>::type
+	_M_enable_shared_from_this_with(const _Yp*) noexcept
+	{ }
+
       void*
       _M_get_deleter(const std::type_info& __ti) const noexcept
       { return _M_refcount._M_get_deleter(__ti); }
@@ -1579,26 +1585,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_M_weak_assign(_Tp1* __p, const __shared_count<_Lp>& __n) const noexcept
 	{ _M_weak_this._M_assign(__p, __n); }
 
-      template<_Lock_policy _Lp1, typename _Tp1, typename _Tp2>
+      friend void
-	friend void
+      __enable_shared_from_this_base(const __shared_count<_Lp>&,
-	__enable_shared_from_this_helper(const __shared_count<_Lp1>&,
+				     const __enable_shared_from_this* __p)
-					 const __enable_shared_from_this<_Tp1,
+      { return __p; }
-					 _Lp1>*, const _Tp2*) noexcept;
 
       mutable __weak_ptr<_Tp, _Lp>  _M_weak_this;
     };
 
-  template<_Lock_policy _Lp1, typename _Tp1, typename _Tp2>
-    inline void
-    __enable_shared_from_this_helper(const __shared_count<_Lp1>& __pn,
-				     const __enable_shared_from_this<_Tp1,
-				     _Lp1>* __pe,
-				     const _Tp2* __px) noexcept
-    {
-      if (__pe != nullptr)
-	__pe->_M_weak_assign(const_cast<_Tp2*>(__px), __pn);
-    }
-
   template<typename _Tp, _Lock_policy _Lp, typename _Alloc, typename... _Args>
     inline __shared_ptr<_Tp, _Lp>
     __allocate_shared(const _Alloc& __a, _Args&&... __args)

libstdc++-v3/include/experimental/bits/shared_ptr.h

@@ -259,7 +259,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       //	{
       //	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
       //	  _M_ptr = static_cast<_Tp*>(__p);
-      //	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
       //	}
 
       // __weak_ptr::lock()
@@ -557,7 +556,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       //	{
       //	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
       //	  _M_ptr = static_cast<_Tp*>(__p);
-      //	  __enable_shared_from_this_helper(_M_refcount, _M_ptr, _M_ptr);
       //	}
 
       // __weak_ptr::lock()
@@ -740,16 +738,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Tp1, typename = _SafeConv<_Tp1>>
 	explicit
-	shared_ptr(_Tp1* __p) : _Base_type(__p) { }
+	shared_ptr(_Tp1* __p) : _Base_type(__p)
+	{ _M_enable_shared_from_this_with(__p); }
 
       template<typename _Tp1, typename _Deleter, typename = _SafeConv<_Tp1>>
 	shared_ptr(_Tp1* __p, _Deleter __d)
-	: _Base_type(__p, __d) { }
+	: _Base_type(__p, __d)
+	{ _M_enable_shared_from_this_with(__p); }
 
       template<typename _Tp1, typename _Deleter, typename _Alloc,
 	       typename = _SafeConv<_Tp1>>
 	shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
-	: _Base_type(__p, __d, __a) { }
+	: _Base_type(__p, __d, __a)
+	{ _M_enable_shared_from_this_with(__p); }
 
       template<typename _Deleter>
 	shared_ptr(nullptr_t __p, _Deleter __d)
@@ -785,13 +786,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if _GLIBCXX_USE_DEPRECATED
       template<typename _Tp1, typename = _Compatible<_Tp1>>
 	shared_ptr(std::auto_ptr<_Tp1>&& __r)
-	: _Base_type(std::move(__r)) { }
+	: _Base_type(std::move(__r))
+	{ _M_enable_shared_from_this_with(static_cast<_Tp1*>(this->get())); }
 #endif
 
       template<typename _Tp1, typename _Del,
 	       typename = _UniqCompatible<_Tp1, _Del>>
 	shared_ptr(unique_ptr<_Tp1, _Del>&& __r)
-	: _Base_type(std::move(__r)) { }
+	: _Base_type(std::move(__r))
+	{
+	  // XXX assume conversion from __r.get() to this->get() to __elem_t*
+	  // is a round trip, which might not be true in all cases.
+	  using __elem_t = typename unique_ptr<_Tp1, _Del>::element_type;
+	  _M_enable_shared_from_this_with(static_cast<__elem_t*>(this->get()));
+	}
 
       constexpr shared_ptr(nullptr_t __p)
       : _Base_type(__p) { }
@@ -853,7 +861,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
 		   _Args&&... __args)
 	: _Base_type(__tag, __a, std::forward<_Args>(__args)...)
-	{ }
+	{ _M_enable_shared_from_this_with(this->get()); }
 
       template<typename _Tp1, typename _Alloc, typename... _Args>
 	friend shared_ptr<_Tp1>
@@ -863,6 +871,35 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _Base_type(__r, std::nothrow) { }
 
       friend class weak_ptr<_Tp>;
+
+      template<typename _Yp>
+	using __esft_base_t =
+	  decltype(__expt_enable_shared_from_this_base(std::declval<_Yp*>()));
+
+      // Detect an accessible and unambiguous enable_shared_from_this base.
+      template<typename _Yp, typename = void>
+	struct __has_esft_base
+	: false_type { };
+
+      template<typename _Yp>
+	struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
+	: __bool_constant<!is_array_v<_Tp>> { };  // ignore base for arrays
+
+      template<typename _Yp>
+	typename enable_if<__has_esft_base<_Yp>::value>::type
+	_M_enable_shared_from_this_with(const _Yp* __p) noexcept
+	{
+	  if (auto __base = __expt_enable_shared_from_this_base(__p))
+	    {
+	      __base->_M_weak_this
+		= shared_ptr<_Yp>(*this, const_cast<_Yp*>(__p));
+	    }
+	}
+
+      template<typename _Yp>
+	typename enable_if<!__has_esft_base<_Yp>::value>::type
+	_M_enable_shared_from_this_with(const _Yp*) noexcept
+	{ }
     };
 
   // C++14 §20.8.2.2.7 //DOING
@@ -1258,15 +1295,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
 	{ _M_weak_this._M_assign(__p, __n); }
 
-      template<typename _Tp1>
+      // Found by ADL when this is an associated class.
-	friend void
+      friend const enable_shared_from_this*
-	__enable_shared_from_this_helper(const __shared_count<>& __pn,
+      __expt_enable_shared_from_this_base(const enable_shared_from_this* __p)
-					 const enable_shared_from_this* __pe,
+      { return __p; }
-					 const _Tp1* __px) noexcept
+
-	{
+      template<typename>
-	  if(__pe != 0)
+	friend class shared_ptr;
-	    __pe->_M_weak_assign(const_cast<_Tp1*>(__px), __pn);
-	}
 
       mutable weak_ptr<_Tp> _M_weak_this;
     };

libstdc++-v3/testsuite/experimental/memory/shared_ptr/cons/enable_shared_from_this.cc

@@ -0,0 +1,47 @@
+// Copyright (C) 2016 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 run { target c++14 } }
+
+#include <experimental/memory>
+#include <testsuite_hooks.h>
+
+struct A : std::enable_shared_from_this<A> { };
+struct B : std::experimental::enable_shared_from_this<B> { };
+struct C : A, B { };
+
+void
+test01()
+{
+  // This should not fail to compile due to ambiguous base classes:
+  std::experimental::shared_ptr<C> p(new C);
+
+  // And both base classes should have been enabled:
+  std::shared_ptr<A> pa = p->A::shared_from_this();
+  VERIFY( pa != nullptr );
+  // Can't compare pa and p because they're different types
+
+  std::experimental::shared_ptr<B> pb = p->B::shared_from_this();
+  VERIFY( pb != nullptr );
+  VERIFY( pb == p );
+}
+
+int
+main()
+{
+  test01();
+}

libstdc++-v3/testsuite/experimental/memory/shared_ptr/cons/unique_ptr_ctor.cc

@@ -83,7 +83,16 @@ test02()
   VERIFY( sp.get() != 0 );
   VERIFY( sp.use_count() == 1 );
 
-  VERIFY( sp[0].shared_from_this() != nullptr );
+  bool caught = false;
+  try
+  {
+    sp[0].shared_from_this(); // should not be set for arrays
+  }
+  catch (const std::bad_weak_ptr&)
+  {
+    caught = true;
+  }
+  VERIFY( caught );
 
   sp.reset();
   VERIFY( destroyed == 5 );