[Bug c++/80475] New: Unevaluated combined delete new expression doesn't handle access error in class template SFINAE

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80475

            Bug ID: 80475
           Summary: Unevaluated combined delete new expression doesn't
                    handle access error in class template SFINAE
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daniel.kruegler at googlemail dot com
  Target Milestone: ---

The following code, compiled with gcc 7.0.1 20170419 (experimental) using the
flags

-Wall -Wextra -std=c++11 -pedantic

or - alternatively -

-Wall -Wextra -std=c++1z -pedantic

//---
struct true_type 
{
  static const bool value = true;
};

struct false_type 
{
  static const bool value = false;
};

template<class T>
T&& declval();

template<typename T, typename Arg, typename = void>
struct is_direct_constructible_impl : false_type
{ };

template<typename T, typename Arg>
struct is_direct_constructible_impl<T, Arg,
      decltype(::delete ::new T(declval<Arg>()))>
    : true_type
{ };

struct S
{
  S(int);
};

struct DCS
{
  DCS(int) = delete;
};

struct PCS
{
private:
  PCS(int);
};

struct DDS 
{
  DDS(int);
  ~DDS() = delete;
};

struct PDS 
{
  PDS(int);
private:
  ~PDS() = default;
};

int main() 
{
  static_assert(is_direct_constructible_impl<S, int>::value, "Ouch");
  static_assert(!is_direct_constructible_impl<DCS, int>::value, "Ouch");
  static_assert(!is_direct_constructible_impl<PCS, int>::value, "Ouch");
  static_assert(!is_direct_constructible_impl<DDS, int>::value, "Ouch");
  static_assert(!is_direct_constructible_impl<PDS, int>::value, "Ouch");
}
//---

is rejected with the following diagnostics:

<quote>
prog.cc: In instantiation of 'struct is_direct_constructible_impl<PCS, int>':
prog.cc:57:56:   required from here
prog.cc:20:25: error: 'PCS::PCS(int)' is private within this context
       decltype(::delete ::new T(declval<Arg>()))>
                         ^~~~~~~~~~~~~~~~~~~~~~~
prog.cc:37:3: note: declared private here
   PCS(int);
   ^~~
prog.cc:20:25: error: 'PCS::PCS(int)' is private within this context
       decltype(::delete ::new T(declval<Arg>()))>
                         ^~~~~~~~~~~~~~~~~~~~~~~
prog.cc:37:3: note: declared private here
   PCS(int);
   ^~~
prog.cc: In function 'int main()':
prog.cc:57:3: error: static assertion failed: Ouch
   static_assert(!is_direct_constructible_impl<PCS, int>::value, "Ouch");
   ^~~~~~~~~~~~~
prog.cc:57:18: error: 'PCS::PCS(int)' is private within this context
   static_assert(!is_direct_constructible_impl<PCS, int>::value, "Ouch");
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
prog.cc:37:3: note: declared private here
   PCS(int);
   ^~~
prog.cc: In instantiation of 'struct is_direct_constructible_impl<PDS, int>':
prog.cc:59:56:   required from here
prog.cc:22:1: error: 'PDS::~PDS()' is private within this context
 { };
 ^
prog.cc:50:3: note: declared private here
   ~PDS() = default;
   ^
prog.cc:22:1: error: 'PDS::~PDS()' is private within this context
 { };
 ^
prog.cc:50:3: note: declared private here
   ~PDS() = default;
   ^
prog.cc:59:3: error: static assertion failed: Ouch
   static_assert(!is_direct_constructible_impl<PDS, int>::value, "Ouch");
   ^~~~~~~~~~~~~
prog.cc:59:18: error: 'PDS::~PDS()' is private within this context
   static_assert(!is_direct_constructible_impl<PDS, int>::value, "Ouch");
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
prog.cc:50:3: note: declared private here
   ~PDS() = default;
   ^
</quote>

This code example is somewhat different from PR 51222 because it uses "class
template SFINAE" and is maybe related to PR 61806. 

This example occurred while discussing a possible alternative implementation of
is_constructible, see PR 80390.