[llvm-bugs] [Bug 38247] New: static constexpr variable member template causes clang crash

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38247

            Bug ID: 38247
           Summary: static constexpr variable member template causes clang
                    crash
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: okannen at gmail.com
                CC: llvm-bugs at lists.llvm.org

A basic C++14 construct make Clang crash for all versions of Clang supporting
C++14 I have tested (clang 3.5 to clang 6.0.1).

The use of static constexpr variable member template make clang crash, example:

#include<type_traits>
using namespace std;

struct A{};
struct B{};

template<class U>
struct test
  {
  template<class T>
  static constexpr bool asame =is_same<T,U>::value ;

  using type =  conditional_t< asame<A> ,B ,A>;

  static constexpr bool asameA =test<U>::asame<A> ;
  };

static_assert(test<A>::asameA,""); //=> static expression is not an integral
constant expression
static_assert(test<B>::asameA,""); //=> static expression is not an integral
constant expression
static_assert(is_same<A,typename test<A>::type>::value,""); //=> ok, but
static_assert(is_same<B,typename test<A>::type>::value,""); //=> also ok! ->
then clang crash in real code base

For those having the issue, the solution is to replace member variable template
by member of a template class as in:

template<class U>
struct test
  {
  template<class T>
  struct fix_clang{
    static constexpr bool asame =is_same<T,U>::value ;
    }

  using type =  conditional_t< fix_clang<A>::asame ,B ,A>;

  static constexpr bool asameA =test<U>::fix_clang<A>::asame ;
  };

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