[Bug libstdc++/100630] New: Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[Bug libstdc++/100630] New: Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[romain.geissler at amadeus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

            Bug ID: 100630
           Summary: Unexpected implicit conversion from volatile bool& to
                    std::filesystem::path in gcc <= 10
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: romain.geissler at amadeus dot com
  Target Milestone: ---

Hi,

I came across this issue today (which I think is unexpected) with gcc 8, 9 and
10. It seems that the following code triggers some implicit conversion from
volatile bool& to std::filesystem::path while this was definitely not the
intention:

#include <filesystem>
#include <iostream>

class Printer
{
    public:
        Printer& operator<<(bool iValue)
        {
            std::cout << __PRETTY_FUNCTION__<< ": " << std::boolalpha << iValue
<< std::endl;

            return *this;
        };

        Printer& operator<<(const std::filesystem::path& iPath)
        {
            std::cout << __PRETTY_FUNCTION__<< ": " << std::boolalpha << iPath
<< std::endl;

            return *this;
        };
};

int main()
{
    Printer aPrinter;
    volatile bool a = false;

    aPrinter << a;
};


It raises the following error (for example using gcc 10 in Compiler Explorer):

In file included from
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/filesystem:45,
                 from <source>:1:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
instantiation of 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
error: no matching function for call to '__is_path_src(volatile bool, int)'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5: note:
candidate: 'template<class _Iter>
std::filesystem::__cxx11::__detail::__is_path_iter_src<_Iter>
std::filesystem::__cxx11::__detail::__is_path_src(_Iter, int)'
   95 |     __is_path_src(_Iter, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5: note:
  template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
substitution of 'template<class _Iter, class _Iter_traits> using
__is_path_iter_src = std::__and_<std::__or_<std::is_same<typename
std::remove_const<typename _Iter_traits::value_type>::type, char>,
std::is_same<typename std::remove_const<typename
_Iter_traits::value_type>::type, wchar_t>, std::is_same<typename
std::remove_const<typename _Iter_traits::value_type>::type, char16_t>,
std::is_same<typename std::remove_const<typename
_Iter_traits::value_type>::type, char32_t> >,
std::is_base_of<std::input_iterator_tag, typename
_Iter_traits::iterator_category> > [with _Iter = bool; _Iter_traits =
std::iterator_traits<bool>]':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5:  
required by substitution of 'template<class _Iter>
std::filesystem::__cxx11::__detail::__is_path_iter_src<_Iter>
std::filesystem::__cxx11::__detail::__is_path_src(_Iter, int) [with _Iter =
bool]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:  
required from 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:88:11:
error: no type named 'value_type' in 'struct std::iterator_traits<bool>'
   88 |     using __is_path_iter_src
      |           ^~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
instantiation of 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:99:5: note:
candidate: 'template<class _CharT, class _Traits, class _Alloc>
std::filesystem::__cxx11::__detail::__is_encoded_char<_CharT>
std::filesystem::__cxx11::__detail::__is_path_src(const
std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&, int)'
   99 |     __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:99:5: note:
  template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits,
_Allocator>' and 'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:103:5:
note: candidate: 'template<class _CharT, class _Traits>
std::filesystem::__cxx11::__detail::__is_encoded_char<_CharT>
std::filesystem::__cxx11::__detail::__is_path_src(const
std::basic_string_view<_CharT, _Traits>&, int)'
  103 |     __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:103:5:
note:   template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
note:   mismatched types 'const std::basic_string_view<_CharT, _Traits>' and
'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:107:5:
note: candidate: 'std::false_type
std::filesystem::__cxx11::__detail::__is_path_src(const _Unknown&, ...) [with
_Unknown = volatile bool; std::false_type = std::integral_constant<bool,
false>]' (near match)
  107 |     __is_path_src(const _Unknown&, ...);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:107:5:
note:   conversion of argument 1 would be ill-formed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
error: cannot bind non-const lvalue reference of type 'const volatile bool&' to
an rvalue of type 'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
ASM generation compiler returned: 1
In file included from
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/filesystem:45,
                 from <source>:1:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
instantiation of 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
error: no matching function for call to '__is_path_src(volatile bool, int)'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5: note:
candidate: 'template<class _Iter>
std::filesystem::__cxx11::__detail::__is_path_iter_src<_Iter>
std::filesystem::__cxx11::__detail::__is_path_src(_Iter, int)'
   95 |     __is_path_src(_Iter, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5: note:
  template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
substitution of 'template<class _Iter, class _Iter_traits> using
__is_path_iter_src = std::__and_<std::__or_<std::is_same<typename
std::remove_const<typename _Iter_traits::value_type>::type, char>,
std::is_same<typename std::remove_const<typename
_Iter_traits::value_type>::type, wchar_t>, std::is_same<typename
std::remove_const<typename _Iter_traits::value_type>::type, char16_t>,
std::is_same<typename std::remove_const<typename
_Iter_traits::value_type>::type, char32_t> >,
std::is_base_of<std::input_iterator_tag, typename
_Iter_traits::iterator_category> > [with _Iter = bool; _Iter_traits =
std::iterator_traits<bool>]':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:95:5:  
required by substitution of 'template<class _Iter>
std::filesystem::__cxx11::__detail::__is_path_iter_src<_Iter>
std::filesystem::__cxx11::__detail::__is_path_src(_Iter, int) [with _Iter =
bool]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:  
required from 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:88:11:
error: no type named 'value_type' in 'struct std::iterator_traits<bool>'
   88 |     using __is_path_iter_src
      |           ^~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h: In
instantiation of 'struct
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>':
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:138:12:  
required from 'struct std::__and_<std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/type_traits:143:12:  
required from 'struct std::__and_<std::__not_<std::is_same<bool,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<volatile bool> >,
std::filesystem::__cxx11::__detail::__constructible_from<volatile bool, void>
>'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:123:11:  
required by substitution of 'template<class _Tp1, class _Tp2> using _Path =
typename std::enable_if<std::__and_<std::__not_<std::is_same<typename
std::remove_cv< <template-parameter-1-1> >::type,
std::filesystem::__cxx11::path> >, std::__not_<std::is_void<typename
std::remove_pointer<_Tp>::type> >,
std::filesystem::__cxx11::__detail::__constructible_from<_Tp1, _Tp2> >::value,
std::filesystem::__cxx11::path>::type [with _Tp1 = volatile bool; _Tp2 = void]'
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:223:7:  
required by substitution of 'template<class _Source, class _Require>
std::filesystem::__cxx11::path::path(const _Source&,
std::filesystem::__cxx11::path::format) [with _Source = volatile bool; _Require
= <missing>]'
<source>:27:17:   required from here
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:99:5: note:
candidate: 'template<class _CharT, class _Traits, class _Alloc>
std::filesystem::__cxx11::__detail::__is_encoded_char<_CharT>
std::filesystem::__cxx11::__detail::__is_path_src(const
std::__cxx11::basic_string<_CharT, _Traits, _Allocator>&, int)'
   99 |     __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:99:5: note:
  template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits,
_Allocator>' and 'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:103:5:
note: candidate: 'template<class _CharT, class _Traits>
std::filesystem::__cxx11::__detail::__is_encoded_char<_CharT>
std::filesystem::__cxx11::__detail::__is_path_src(const
std::basic_string_view<_CharT, _Traits>&, int)'
  103 |     __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:103:5:
note:   template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
note:   mismatched types 'const std::basic_string_view<_CharT, _Traits>' and
'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:107:5:
note: candidate: 'std::false_type
std::filesystem::__cxx11::__detail::__is_path_src(const _Unknown&, ...) [with
_Unknown = volatile bool; std::false_type = std::integral_constant<bool,
false>]' (near match)
  107 |     __is_path_src(const _Unknown&, ...);
      |     ^~~~~~~~~~~~~
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:107:5:
note:   conversion of argument 1 would be ill-formed:
/opt/compiler-explorer/gcc-10.3.0/include/c++/10.3.0/bits/fs_path.h:119:29:
error: cannot bind non-const lvalue reference of type 'const volatile bool&' to
an rvalue of type 'volatile bool'
  119 |     : decltype(__is_path_src(std::declval<_Source>(), 0))
      |                ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
Execution build compiler returned: 1



It seems that it works in gcc 11, and I guess this comes from this commit:

commit 988b853f9c829742907ae22ac66de56facfc7bc5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat May 23 07:28:40 2020 +0100

    libstdc++: Simplify filesystem::path SFINAE constraints

(which seems to have a few follow-up commits to fix some issues).

Shall these SFINAE changes be backported to gcc 9/10 (and I know that gcc 8 was
just closed, but in my case I would be interested by a gcc 8 backport too) ?

Cheers,
Romain

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-05-17
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Romain Geissler from comment #0)
> Hi,
> 
> I came across this issue today (which I think is unexpected) with gcc 8, 9
> and 10. It seems that the following code triggers some implicit conversion
> from volatile bool& to std::filesystem::path while this was definitely not
> the intention:

It's not triggering such a conversion, it's checking if such a conversion is
viable as part of overload resolution. But then that instantiates something
that is ill-formed and fails with an error outside the immediate context.

I think the right fix for the branches is:


--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -116,7 +116,7 @@ namespace __detail

   template<typename _Source>
     struct __constructible_from<_Source, void>
-    : decltype(__is_path_src(std::declval<_Source>(), 0))
+    : decltype(__is_path_src(std::declval<const _Source&>(), 0))
     { };

   template<typename _Tp1, typename _Tp2 = void>

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:4cd69a5a0dd31bc6fdef1bbabc8d6d1416014ea1

commit r10-9831-g4cd69a5a0dd31bc6fdef1bbabc8d6d1416014ea1
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 17 11:54:06 2021 +0100

    libstdc++: Fix filesystem::path constraints for volatile [PR 100630]

    The constraint check for filesystem::path construction uses
    decltype(__is_path_src(declval<Source>())) which mean it considers
    conversion from an rvalue.  When Source is a volatile-qualified type
    it cannot use is_path_src(const Unknown&) because a const lvalue
    reference can only bind to a non-volatile rvalue.

    Since the relevant path members all have a const Source& parameter,
    the constraint should be defined in terms of declval<const Source&>(),
    not declval<Source>(). This avoids the problem of volatile-qualified
    rvalues, because we no longer use an rvalue at all.

    libstdc++-v3/ChangeLog:

            PR libstdc++/100630
            * include/bits/fs_path.h (__is_constructible_from): Test
            construction from a const lvalue, not an rvalue.
            * include/experimental/bits/fs_path.h (__is_constructible_from):
            Likewise.
            * testsuite/27_io/filesystem/path/construct/100630.cc: New test.
            * testsuite/experimental/filesystem/path/construct/100630.cc:
            New test.

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

--- Comment #3 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:45aa7a447652e8541cc381d7ab128544f81ed857

commit r12-845-g45aa7a447652e8541cc381d7ab128544f81ed857
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 17 11:54:06 2021 +0100

    libstdc++: Fix filesystem::path constraints for volatile [PR 100630]

    The constraint check for filesystem::path construction uses
    decltype(__is_path_src(declval<Source>())) which mean it considers
    conversion from an rvalue.  When Source is a volatile-qualified type
    it cannot use is_path_src(const Unknown&) because a const lvalue
    reference can only bind to a non-volatile rvalue.

    Since the relevant path members all have a const Source& parameter,
    the constraint should be defined in terms of declval<const Source&>(),
    not declval<Source>(). This avoids the problem of volatile-qualified
    rvalues, because we no longer use an rvalue at all.

    libstdc++-v3/ChangeLog:

            PR libstdc++/100630
            * include/experimental/bits/fs_path.h (__is_constructible_from):
            Test construction from a const lvalue, not an rvalue.
            * testsuite/27_io/filesystem/path/construct/100630.cc: New test.
            * testsuite/experimental/filesystem/path/construct/100630.cc:
            New test.

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:f8d2cef5c544dd0196ec5a6f479fbf96d2214d76

commit r11-8425-gf8d2cef5c544dd0196ec5a6f479fbf96d2214d76
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 17 11:54:06 2021 +0100

    libstdc++: Fix filesystem::path constraints for volatile [PR 100630]

    The constraint check for filesystem::path construction uses
    decltype(__is_path_src(declval<Source>())) which mean it considers
    conversion from an rvalue.  When Source is a volatile-qualified type
    it cannot use is_path_src(const Unknown&) because a const lvalue
    reference can only bind to a non-volatile rvalue.

    Since the relevant path members all have a const Source& parameter,
    the constraint should be defined in terms of declval<const Source&>(),
    not declval<Source>(). This avoids the problem of volatile-qualified
    rvalues, because we no longer use an rvalue at all.

    libstdc++-v3/ChangeLog:

            PR libstdc++/100630
            * include/experimental/bits/fs_path.h (__is_constructible_from):
            Test construction from a const lvalue, not an rvalue.
            * testsuite/27_io/filesystem/path/construct/100630.cc: New test.
            * testsuite/experimental/filesystem/path/construct/100630.cc:
            New test.

    (cherry picked from commit 45aa7a447652e8541cc381d7ab128544f81ed857)

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[romain.geissler at amadeus dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

--- Comment #5 from Romain Geissler <romain.geissler at amadeus dot com> ---
Hi,

Thanks for providing a fix that quickly !

I backported it in my own copy of gcc 8 and 9 and it fixed my issue on these
branches as well.

Cheers,
Romain

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |9.5

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It's too late for 9.4 but I plan to backport it for 9.5

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:3c805829c9023da48db6d636221fd79612dff7ea

commit r9-9593-g3c805829c9023da48db6d636221fd79612dff7ea
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 17 11:54:06 2021 +0100

    libstdc++: Fix filesystem::path constraints for volatile [PR 100630]

    The constraint check for filesystem::path construction uses
    decltype(__is_path_src(declval<Source>())) which mean it considers
    conversion from an rvalue.  When Source is a volatile-qualified type
    it cannot use is_path_src(const Unknown&) because a const lvalue
    reference can only bind to a non-volatile rvalue.

    Since the relevant path members all have a const Source& parameter,
    the constraint should be defined in terms of declval<const Source&>(),
    not declval<Source>(). This avoids the problem of volatile-qualified
    rvalues, because we no longer use an rvalue at all.

    libstdc++-v3/ChangeLog:

            PR libstdc++/100630
            * include/bits/fs_path.h (__is_constructible_from): Test
            construction from a const lvalue, not an rvalue.
            * include/experimental/bits/fs_path.h (__is_constructible_from):
            Likewise.
            * testsuite/27_io/filesystem/path/construct/100630.cc: New test.
            * testsuite/experimental/filesystem/path/construct/100630.cc:
            New test.

    (cherry picked from commit 4cd69a5a0dd31bc6fdef1bbabc8d6d1416014ea1)

[Bug libstdc++/100630] Unexpected implicit conversion from volatile bool& to std::filesystem::path in gcc <= 10

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100630

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

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

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for 9.5, 10.4 and 11.2