[Bug libstdc++/107049] New: error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[Bug libstdc++/107049] New: error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

            Bug ID: 107049
           Summary: error: ‘std::__cxx11::basic_string<_CharT, _Traits,
                    _Alloc>::operator __sv_type() const [with _CharT =
                    char; _Traits = std::char_traits<char>; _Alloc =
                    std::allocator<char>; __sv_type =
                    std::basic_string_view<char>]’ is inaccessible within
                    this context
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jwakely.gcc at gmail dot com
  Target Milestone: ---

Must be very recent change:

g++ pdf.ii -c
In file included from /usr/include/glib-2.0/glib/glib-typeof.h:41,
                 from /usr/include/glib-2.0/glib/gatomic.h:30,
                 from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34,
                 from /usr/include/glibmm-2.4/glibmm/unicode.h:23,
                 from /usr/include/glibmm-2.4/glibmm/ustring.h:21,
                 from /usr/include/gtkmm-3.0/gtkmm/dialog.h:6,
                 from
/home/abuild/rpmbuild/BUILD/inkscape-1.2.1_2022-07-14_9c6d41e410/src/extension/internal/pdfinput/pdf-input.h:21,
                 from
/home/abuild/rpmbuild/BUILD/inkscape-1.2.1_2022-07-14_9c6d41e410/src/extension/internal/pdfinput/pdf-input.cpp:19:
/usr/include/c++/13/type_traits: In instantiation of ‘struct
std::is_convertible<const GooString&, std::basic_string_view<char> >’:
/usr/include/c++/13/type_traits:161:35:   required by substitution of
‘template<class ... _Bn> std::__detail::__first_t<std::integral_constant<bool,
true>, typename std::enable_if<(bool)(_Bn::value), void>::type ...>
std::__detail::__and_fn(int) [with _Bn = {std::is_convertible<const GooString&,
std::basic_string_view<char, std::char_traits<char> > >,
std::__not_<std::is_convertible<const GooString*, const
std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>
>*> >, std::__not_<std::is_convertible<const GooString&, const char*> >}]’
/usr/include/c++/13/type_traits:177:42:   required from ‘struct
std::__and_<std::is_convertible<const GooString&, std::basic_string_view<char,
std::char_traits<char> > >, std::__not_<std::is_convertible<const GooString*,
const std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >*> >, std::__not_<std::is_convertible<const GooString&,
const char*> > >’
/usr/include/c++/13/bits/basic_string.h:155:8:   required by substitution of
‘template<class _CharT, class _Traits, class _Alloc> template<class _Tp, class
_Res> using std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_If_sv =
std::enable_if_t<std::__and_<std::is_convertible<const _Tp&,
std::basic_string_view<_CharT, _Traits> >,
std::__not_<std::is_convertible<const _Tp*, const
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>*> >,
std::__not_<std::is_convertible<const _Tp&, const _CharT*> > >::value, _Res>
[with _Tp = GooString; _Res = std::__cxx11::basic_string<char>&; _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’
/usr/include/c++/13/bits/basic_string.h:1493:9:   required by substitution of
‘template<class _Tp> std::__cxx11::basic_string<char>::_If_sv<_Tp,
std::__cxx11::basic_string<char>&>
std::__cxx11::basic_string<char>::append(const _Tp&) [with _Tp = GooString]’
/usr/include/poppler/goo/GooString.h:112:49:   required from here
/usr/include/c++/13/type_traits:1387:30: error:
‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type()
const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is
inaccessible within this context
In file included from /usr/include/c++/13/string:52,
                 from /usr/include/c++/13/bits/locale_classes.h:40,
                 from /usr/include/c++/13/bits/ios_base.h:41,
                 from /usr/include/c++/13/streambuf:41,
                 from /usr/include/c++/13/bits/streambuf_iterator.h:35,
                 from /usr/include/c++/13/iterator:66,
                 from /usr/include/glibmm-2.4/glibmm/ustring.h:25:
/usr/include/c++/13/bits/basic_string.h:936:7: note: declared here

[Bug libstdc++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Created attachment 53632
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53632&action=edit
Unreduced test-case

[Bug libstdc++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-09-27
     Ever confirmed|0                           |1

[Bug libstdc++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|jwakely.gcc at gmail dot com       |mpolacek at gcc dot gnu.org
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It's a front-end bug in the __is_convertible built-in.

Reduced:

template<bool B>
struct bool_constant { static constexpr bool value = B; };
using true_type = bool_constant<true>;
using false_type = bool_constant<false>;

template<typename T> struct is_void : false_type { };
template<> struct is_void<void> : true_type { };

template<bool> struct enable_if { };
template<> struct enable_if<true> { using type = void; };
template<bool B> using enable_if_t = typename enable_if<B>::type;

#ifndef NO_BUILTIN
  template<typename _From, typename _To>
    struct is_convertible
    : public bool_constant<__is_convertible(_From, _To)>
    { };
#else

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

  template<typename _From, typename _To,
           bool = is_void<_From>::value>
    struct __is_convertible_helper
    {
      typedef typename is_void<_To>::type type;
    };

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
  template<typename _From, typename _To>
    class __is_convertible_helper<_From, _To, false>
    {
      template<typename _To1>
        static void __test_aux(_To1) noexcept;

      template<typename _From1, typename _To1,
               typename = decltype(__test_aux<_To1>(declval<_From1>()))>
        static true_type
        __test(int);

      template<typename, typename>
        static false_type
        __test(...);

    public:
      typedef decltype(__test<_From, _To>(0)) type;
    };
#pragma GCC diagnostic pop

  /// is_convertible
  template<typename _From, typename _To>
    struct is_convertible
    : public __is_convertible_helper<_From, _To>::type
    { };
#endif

struct string_view { };

struct string
{
private:
  template<class T>
    using If_sv = enable_if_t<is_convertible<const T&, string_view>::value>;

public:
  void append(const string&) { }
  template<class T> If_sv<T> append(const T&) { }

  operator string_view() const { return {}; }
};


struct PrivateString : private string
{
  void f()
  {
    const auto& cthis = *this;
    static_cast<string&>(*this).append(cthis);
  }
};


conv.cc: In instantiation of 'struct is_convertible<const PrivateString&,
string_view>':
conv.cc:68:11:   required by substitution of 'template<class T> using
string::If_sv = enable_if_t<is_convertible<const T&, string_view>::value> [with
T = PrivateString]'
conv.cc:72:30:   required by substitution of 'template<class T>
string::If_sv<T> string::append(const T&) [with T = PrivateString]'
conv.cc:83:39:   required from here
conv.cc:16:28: error: 'string::operator sv_type() const' is inaccessible within
this context
   16 |     : public bool_constant<__is_convertible(_From, _To)>
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
conv.cc:74:3: note: declared here
   74 |   operator sv_type() const { return {}; }
      |   ^~~~~~~~


Using -DNO_BUILTIN it works, so I'll revert the library change to use
__is_convertible.

[Bug libstdc++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #2)
>   template<class T>
>     using If_sv = enable_if_t<is_convertible<const T&, string_view>::value>;

It works if this is changed to:

  template<class T>
    using If_sv = enable_if_t<__is_convertible(const T&, string_view)>;

So the problem is that it fails an access check when the built-in is used
outside the class body. But that should be a SFINAE context.


Further reduced:

template<bool B>
struct bool_constant { static constexpr bool value = B; };

template<typename From, typename To>
struct is_convertible
: public bool_constant<__is_convertible(From, To)>
{ };

template<bool> struct enable_if { };
template<> struct enable_if<true> { using type = void; };
template<bool B> using enable_if_t = typename enable_if<B>::type;


class Private
{
  operator int() const;

public:
  void f(const Private&);

  template<class T>
    enable_if_t<is_convertible<T, int>::value>
    f(T)
    { }
};

int main()
{
  Private p;
  p.f(p);
}

sfinae.cc: In instantiation of 'struct is_convertible<Private, int>':
sfinae.cc:23:5:   required by substitution of 'template<class T>
enable_if_t<is_convertible<T, int>::value> Private::f(T) [with T = Private]'
sfinae.cc:30:6:   required from here
sfinae.cc:6:24: error: 'Private::operator int() const' is private within this
context
    6 | : public bool_constant<__is_convertible(From, To)>
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~
sfinae.cc:16:3: note: declared private here
   16 |   operator int() const;
      |   ^~~~~~~~

[Bug libstdc++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Further reduced:

template<bool B>
struct bool_constant { static constexpr bool value = B; };

template<typename From, typename To>
struct is_convertible
: public bool_constant<__is_convertible(From, To)>
{ };

class Private
{
  operator int() const;
};

static_assert( not is_convertible<Private, int>::value, "" );


sfinae.cc: In instantiation of 'struct is_convertible<Private, int>':
sfinae.cc:14:48:   required from here
sfinae.cc:6:24: error: 'Private::operator int() const' is private within this
context
    6 | : public bool_constant<__is_convertible(From, To)>
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~
sfinae.cc:11:3: note: declared private here
   11 |   operator int() const;
      |   ^~~~~~~~
sfinae.cc:14:16: error: static assertion failed
   14 | static_assert( not is_convertible<Private, int>::value, "" );
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Bug c++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |c++

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Testing this fix:

--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2246,6 +2246,7 @@ is_convertible_helper (tree from, tree to)
     return integer_one_node;
   cp_unevaluated u;
   tree expr = build_stub_object (from);
+  deferring_access_check_sentinel acs (dk_no_deferred);
   return perform_implicit_conversion (to, expr, tf_none);
 }

[Bug c++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
   Target Milestone|---                         |13.0

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Patch posted:
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/602327.html

[Bug c++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:3f7eea4411e4b2d8a500d9272b2ed72f73bdd008

commit r13-2898-g3f7eea4411e4b2d8a500d9272b2ed72f73bdd008
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Sep 27 09:51:10 2022 +0100

    c++: Make __is_{,nothrow_}convertible SFINAE on access  [PR107049]

    The is_convertible built-ins should return false if the conversion fails
    an access check, not report an error.

            PR c++/107049

    gcc/cp/ChangeLog:

            * method.cc (is_convertible_helper): Use access check sentinel.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/is_convertible4.C: New test.
            * g++.dg/ext/is_nothrow_convertible4.C: New test.

    libstdc++-v3/ChangeLog:

            * testsuite/20_util/is_convertible/requirements/access.cc: New
            test.

[Bug c++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Patch approved and committed.

[Bug c++/107049] error: ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator __sv_type() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; __sv_type = std::basic_string_view<char>]’ is inaccessible within this context

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107049

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ville.voutilainen at gmail dot com

--- Comment #9 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Just a historical anecdote of something eerily similar in so many ways,
including Jonathan's reduction and its steps :) :
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94197