Bug: legitimate code with variadic templates and variadic template aliases leads to an error.

[Mikhail_K_3]

Hi,

I've got an issue with the following code:

In test.cpp

    template <typename... Types>
    struct Variadic1 {};

    template <typename... Types>
    using MakeVariadic1 = Variadic1<Types...>;

    template <typename... Types>
    struct Variadic2 {};

    template <typename... Types>
    using MakeVariadic2 = Variadic2<MakeVariadic1<Types...>>;

    template <typename... Types>
    MakeVariadic2<Types...> test(Types...)
    {
        return MakeVariadic2<Types...>();
    }

    int main()
    {
        test(1);
    }

Command line and output:

 ~/tmp$ ~/soft/intel/system_studio_2015.2.050/bin/ia32/icpc -std=c++11 test.cpp -o test
test.cpp(21): error: template instantiation resulted in unexpected function type of "MakeVariadic2<int> (int)" (the meaning of a name may have changed since the template declaration -- the type of the template is "MakeVariadic2<Types...> (Types...)")
      test(1);
             ^
          detected during instantiation of "test" based on template argument <int> at line 21

compilation aborted for test.cpp (code 2)

~/tmp$ ~/soft/intel/system_studio_2015.2.050/bin/ia32/icpc --version
icpc (ICC) 15.0.0 20150121
Copyright (C) 1985-2015 Intel Corporation.  All rights reserved.

Note that Clang (3.4.1) and GCC (4.9.1) compile this code without errors.

Mikhail.

[Judith_W_Intel]

Yes this definitely looks like a bug and I can reproduce it with our latest development compiler. I have entered this in our internal bug tracking database as DPD200368349.

Thanks for reporting it and for the concise example!

Judy

[Judith_W_Intel]

We are still working on this one.

In the meantime the workaround is to not use the template alias in the return type for test(), i.e. change it the code inside #ifdef OK:

template <typename... Types>
#ifdef OK
Variadic2<Variadic1<Types...>>
#else
MakeVariadic2<Types...>
#endif
test(Types...)

instead of:

MakeVariadic2<Types...> test(Types...)

Judy