[Bug c++/109084] New: requires keyword can't access private static constexpr bool in templated class

["brignon.enzo at protonmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109084

            Bug ID: 109084
           Summary: requires keyword can't access private static constexpr
                    bool in templated class
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: brignon.enzo at protonmail dot com
  Target Milestone: ---

Created attachment 54626
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54626&action=edit
The minimal reproduction file (not preprocessed because it does not include
anything)

When using requires keyword to enable class member function using a private
static constexpr bool (eventually the value of a concept) in a templated class
gcc fails to access the given boolean variable because it is private within its
context. 
It does not fail if the boolean is public or if the class is not templated.

You can find a minimal example (not preprocessed because it needs no include)
in attachment.

Output of gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.1 20230201 (GCC) 

The file is complied with following options:
g++ -std=c++20 bug.cpp

Output of gcc:

bug.cpp: In function 'int main()':
bug.cpp:12:15: error: class template argument deduction failed:
   12 |     MyClass c{};
      |               ^
bug.cpp:12:15: error: no matching function for call to 'MyClass()'
bug.cpp:8:5: note: candidate: 'template<class T, class Enable>  requires 
MyClass<T>::cond MyClass()-> MyClass<T>'
    8 |     MyClass() {}
      |     ^~~~~~~
bug.cpp:8:5: note:   template argument deduction/substitution failed:
bug.cpp:8:5: note: constraints not satisfied
bug.cpp: In substitution of 'template<class T, class Enable>  requires 
MyClass<T>::cond MyClass()-> MyClass<T> [with T = int; Enable = void]':
bug.cpp:12:15:   required from here
bug.cpp:8:5:   required by the constraints of 'template<class T, class Enable> 
requires  MyClass<T>::cond MyClass()-> MyClass<T>'
bug.cpp:12:15: error: 'constexpr const bool MyClass<int>::cond' is private
within this context
   12 |     MyClass c{};
      |               ^
bug.cpp:5:27: note: declared private here
    5 |     static constexpr bool cond = true;
      |                           ^~~~
bug.cpp:3:7: note: candidate: 'template<class T> MyClass(MyClass<T>)->
MyClass<T>'
    3 | class MyClass {
      |       ^~~~~~~
bug.cpp:3:7: note:   template argument deduction/substitution failed:
bug.cpp:12:15: note:   candidate expects 1 argument, 0 provided
   12 |     MyClass c{};
      |