[Bug c++/93699] New: [gcc10] Invalid operator== (returning non-bool type) candidate

[laurent.stacul at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93699

            Bug ID: 93699
           Summary: [gcc10] Invalid operator== (returning non-bool type)
                    candidate
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: laurent.stacul at gmail dot com
  Target Milestone: ---

Hello,

With a HEAD of gcc:

gcc -v                                                                         
                                                                          
[jobs: 2][history: 5226]
Reading specs from
/remote/tools/Linux/2.6/1A/toolchain/x86_64-v20.0.8/bin/../lib/gcc/x86_64-1a-linux-gnu/10.0.1/specs
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/remote/tools/Linux/2.6/1A/toolchain/x86_64-v20.0.8/bin/../libexec/gcc/x86_64-1a-linux-gnu/10.0.1/lto-wrapper
Target: x86_64-1a-linux-gnu
Configured with: /workdir/src/gcc-10.0.1/configure --build=x86_64-1a-linux-gnu
--host=x86_64-1a-linux-gnu --target=x86_64-1a-linux-gnu
--prefix=/opt/1A/toolchain/x86_64-v20.0.8
--with-local-prefix=/opt/1A/toolchain/x86_64-v20.0.8
--with-native-system-header-dir=/opt/1A/toolchain/x86_64-v20.0.8/include
--enable-languages=c,c++,fortran --disable-multilib --enable-linker-build-id
--with-linker-hash-style=gnu --enable-gnu-indirect-function
--with-build-config=bootstrap-lto --enable-install-libiberty
--enable-checking=release
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.0.1 20200211 (experimental) (GCC)

In the following example, I think there is something odd:

class Base {
public:
    virtual int operator==(const Base&) const {
        return 1;
    }
};

class Derived : public Base {
public:
    virtual int operator==(const Base&) const {
        return 1;
    }
};

int main(int argc, const char *argv[])
{
    Base* b;
    Derived* d;
    if (*b == *d) {
        return 1;
    }
    return 0;
}

The compilation is done as follows:

$ g++ -std=gnu++2a rep.cpp

<source>: In function 'int main(int, const char**)':

<source>:19:12: error: return type of 'virtual int Derived::operator==(const
Base&) const' is not 'bool'

   19 |     if (*b == *d) {

      |         ~~~^~~~~

<source>:19:12: note: used as rewritten candidate for comparison of 'Base' and
'Derived'

Compiler returned: 1

I understand that C++20 introduced the possibility for the compiler to have the
reversed primary operator to be candidate in the function resolution, but as
far as I understand the primary comparison operators are not rewritten.

Is there a bug in the C++20 support or did I miss something ?
Regards,
Stac