Boost 1.83 typeid_name Fails For Abstract Base Classes

[canon-cmi-william-hachfeld]

I believe this change made by @pdimov has broken typeid_name for abstract base classes (at least when compiling with MSVC 19.39). Consider the following minimal repro case:

#include <string>
#include <typeinfo>

inline std::string fix_typeid_name(char const* n)
{
    return ""; // Empty Implementation
}

#if defined(USE_BOOST_1_83_VERSION)

// class types can be incomplete
template<class T> std::string typeid_name_impl(int T::*)
{
    std::string r = fix_typeid_name(typeid(T[1]).name());
    return r.substr(0, r.size() - 4); // remove ' [1]' suffix
}

template<class T> std::string typeid_name_impl(...)
{
    return fix_typeid_name(typeid(T).name());
}

template<class T> std::string typeid_name()
{
    return typeid_name_impl<T>(0);
}

#else

template<class T> std::string typeid_name()
{
    return fix_typeid_name(typeid(T).name());
}

#endif

class MyClass
{
    virtual int f() const = 0;
};

std::string test()
{
    return typeid_name<MyClass>();
}

Compiling this with MSVC using the Boost >= 1.83.0 version yields:

D:\Boost_Core_Issue>cl /DUSE_BOOST_1_83_VERSION test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.39.33523 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
test.cpp(15): error C2092: 'abstract declarator' array element type cannot be function or abstract class type
test.cpp(15): note: the template instantiation context (the oldest one first) is
test.cpp(45): note: see reference to function template instantiation 'std::string typeid_name<MyClass>(void)' being compiled
test.cpp(26): note: see reference to function template instantiation 'std::string typeid_name_impl<T>(int MyClass::* )' being compiled
        with
        [
            T=MyClass
        ]

D:\Boost_Core_Issue>

But using the earlier implementation from Boost 1.82.0 compile fine:

D:\Boost_Core_Issue>cl test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.39.33523 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 14.39.33523.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj
LINK : fatal error LNK1561: entry point must be defined

D:\Boost_Core_Issue>

I must admit I don't quite understand what the int T::* syntax is supposed to do exactly, so I'm unclear whether the Microsoft compiler itself could be at fault here. So please do let me know if you believe this is a compiler bug rather than an issue with the code itself. In which case I'll report the issue to Microsoft instead. Thanks in advance for taking a look!

[pdimov]

Thanks, I'll look into it. Various compilers have various limitations for what can go into typeid(T) so it sometimes happens that when I fix one thing, another breaks.

[canon-cmi-william-hachfeld]

Absolutely. Totally understand, Peter. I appreciate you taking a look at whether there is something that can be done on the Boost side to address this.

[pdimov]

Should be fixed by https://github.com/boostorg/core/commit/965508d9e187d589070c5cd1853cc035b51ea3cf.

[canon-cmi-william-hachfeld]

Fantastic. Thank you, @pdimov, for addressing this so quickly!