[Bug c++/86037] New: __PRETTY_FUNCTION__ for constexpr lambda's is missing [with = type]

[gcc-bugs at marehr dot dialup.fu-berlin.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86037

            Bug ID: 86037
           Summary: __PRETTY_FUNCTION__ for constexpr lambda's is missing
                    [with = type]
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc-bugs at marehr dot dialup.fu-berlin.de
  Target Milestone: ---

Hello gcc-team,

this code changed output between gcc-7 and gcc-8

```
// pretty_function.cpp
#include <iostream>
#include <string>

template <typename type>
struct pretty_lambda
{
    static constexpr auto as_string = [] ()
    {
        return std::string{__PRETTY_FUNCTION__};
    };
};

int main()
{
    std::string lambda_int = pretty_lambda<int>::as_string();
    std::cout << lambda_int << "\n";
    return 0;
}
```

compiling with `g++-7 -std=c++17 pretty_function.cpp` outputs:

    pretty_lambda<type>::<lambda()> [with type = int]

compiling with `g++-8 -std=c++17 pretty_function.cpp` outputs:

    pretty_lambda<int>::<lambda()>

Is there a reason for this change? The same class, but with `as_string` as a
static function delivers an output with the `[with type = int]` part
(i.e., `static auto seqan3::detail::pretty_function<type>::as_string() [with
type = int]`).

So it seems to me that the general format was not changed. I know that this is
in no way a standard function or something, but I would prefer a consistent
output.

> g++-7 -v

Using built-in specs.
COLLECT_GCC=g++-7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc7/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,lto
--enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib
--with-isl --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp
--enable-gnu-unique-object --enable-linker-build-id --enable-lto
--enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu
--enable-gnu-indirect-function --disable-werror --enable-checking=release
--enable-default-pie --enable-default-ssp --program-suffix=-7
--enable-version-specific-runtime-libs
Thread model: posix
gcc version 7.3.1 20180406 (GCC)

> g++-8 -v

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --enable-libmpx --with-system-zlib --with-isl
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu
--disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object
--enable-linker-build-id --enable-lto --enable-plugin
--enable-install-libiberty --with-linker-hash-style=gnu
--enable-gnu-indirect-function --enable-multilib --disable-werror
--enable-checking=release --enable-default-pie --enable-default-ssp
Thread model: posix
gcc version 8.1.0 (GCC)

Thank you for your awesome work!
Marcel