[LLVMbugs] [Bug 22942] New: variadic using in variadic struct evaluating bad in struct context but not outside

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=22942

            Bug ID: 22942
           Summary: variadic using in variadic struct evaluating bad in
                    struct context but not outside
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: bloerwald at googlemail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

check<int, int>::u is supposed to be seq<0, 1>, but is seq<0> in context of
check, while it is seq<0, 1> when used outside of check.


#include <type_traits>

template<std::size_t... I> struct seq {
  using next = seq<I..., sizeof... (I)>;
};
template<std::size_t N> struct iota {
  using type = typename iota<N - 1>::type::next;
};
template<> struct iota<0ul> {
  using type = seq<>;
};

template<typename... T> struct seq_for_t {
  using type = typename iota<sizeof... (T)>::type;
};
template<typename... T> using seq_for = typename seq_for_t<T...>::type;

template<typename... T> using seq_for_u = typename iota<sizeof... (T)>::type;

template<typename... T> struct check {
  using n = seq_for  <T...>;
  using u = seq_for_u<T...>;

  using expected = seq<0, 1>;

  static_assert (std::is_same<n, expected>::value, "");
  static_assert (std::is_same<u, expected>::value, ""); /// <<< failing
};

using c = check<int, int>;

static_assert (std::is_same<c::n, c::expected>::value, "");
static_assert (std::is_same<c::u, c::expected>::value, ""); /// <<< NOT failing


$ clang++ -Wno-c++98-compat -Weverything --std=c++11 -c variadic_in_using.cpp
variadic_in_using.cpp:28:3: error: static_assert failed ""
  static_assert (std::is_same<u, expected>::value, "");
  ^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

$ clang++ -v
clang version 3.6.0 (tags/RELEASE_360/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation:
/soft/gcc/4.9.2/lib/gcc/x86_64-unknown-linux-gnu/4.9.2
Selected GCC installation:
/soft/gcc/4.9.2/lib/gcc/x86_64-unknown-linux-gnu/4.9.2
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

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