https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97740
Bug ID: 97740
Summary: Weird error message about accessing a private member
of my own class inside of std::string_view inside of
constexpr
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: markus.boeck02 at gmail dot com
Target Milestone: ---
Created attachment 49513
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49513&action=edit
Reproduction of the bug. Simply compile with -std=c++17
I want to apologize for the code you are about to see already. I am one of
those people who likes to constexpr and templates at times. In one of my recent
code that does some constexpr string parsing and validation I encountered a
very very weird error message:
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/string_view: In
instantiation of
'cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)> [with auto:7 = {const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&}]':
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/type_traits:2506:26:
required by substitution of 'template<class _Fn, class ... _Args> static
std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)),
std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn =
cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>; _Args = {const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&}]'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/type_traits:2517:55:
required from 'struct std::__result_of_impl<false, false,
cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&>'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/type_traits:138:12:
recursively required by substitution of 'template<class _Result, class _Ret>
struct std::__is_invocable_impl<_Result, _Ret, true, std::__void_t<typename
_CTp::type> > [with _Result =
std::__invoke_result<cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&>; _Ret = void]'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/type_traits:138:12:
required from 'struct
std::__and_<std::__is_invocable_impl<std::__invoke_result<cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&>, void, true, void>,
std::__call_is_nothrow<std::__invoke_result<cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&>,
cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&> >'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/type_traits:2979:12:
required from 'struct
std::is_nothrow_invocable<cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::pair<cld::detail::CommandLine::Pointer<(& detail::INCLUDESbind0)>,
std::in_place_type_t<std::basic_string_view<char, std::char_traits<char> > >
>&>'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/tuple:1715:37: required
from 'constexpr const bool std::__unpack_std_tuple<template<class _Fn, class
... _ArgTypes> struct std::is_nothrow_invocable,
cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>, const
std::tuple<std::pair<cld::detail::CommandLine::Pointer<(&
detail::INCLUDESbind0)>, std::in_place_type_t<std::basic_string_view<char,
std::char_traits<char> > > > >&>'
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/tuple:1730:14: required
from 'constexpr decltype(auto) std::apply(_Fn&&, _Tuple&&) [with _Fn =
cld::detail::CommandLine::parseOptions<cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>, {detail::INCLUDESbind0,
std::in_place_type<std::basic_string_view<char, std::char_traits<char> >
>}>::<lambda(auto:7&& ...)>; _Tuple = const
std::tuple<std::pair<cld::detail::CommandLine::Pointer<(&
detail::INCLUDESbind0)>, std::in_place_type_t<std::basic_string_view<char,
std::char_traits<char> > > > >&]'
<source>:456:36: required from 'constexpr auto
cld::detail::CommandLine::parseOptions(std::string_view, cld::CLIMultiArg)
[with T = cld::detail::CommandLine::Pack<detail::INCLUDESarg0,
detail::INCLUDESarg1, detail::INCLUDESarg2>; auto& ...args =
{detail::INCLUDESbind0, std::in_place_type<std::basic_string_view<char,
std::char_traits<char> > >}; std::string_view = std::basic_string_view<char>]'
<source>:502:62: required from here
/opt/compiler-explorer/gcc-10.2.0/include/c++/10.2.0/string_view:287:34: error:
'char cld::Constexpr::basic_fixed_string<char, 7>::m_data [7]' is private
within this context
287 | return basic_string_view{_M_str + __pos, __rlen};
| ~~~~~~~^~~~~~~
<source>:18:5: note: declared private here
18 | T m_data[N] = {};
|
I tried to create a minimum reproducible from scratch but failed to so. Instead
I now used my code and tried to minimize that as much as possible which sadly
still amounts to 500 lines of code but does reproduce the issue. I have
attached the file.
To my knowledge the code is correct and clang and MSVC compile it without
issues. Changing m_data in basic_fixed_string from private to public makes the
build succeed. Every version of GCC 8 to trunk fail with the same error. GCC 7
instead has an internal compiler error.
Alternatively see this compiler explorer link: https://godbolt.org/z/snnfo7
