[Bug c++/89287] New: Array declaration fails to use template conversion operator

[raphael.kubo.da.costa at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89287

            Bug ID: 89287
           Summary: Array declaration fails to use template conversion
                    operator
           Product: gcc
           Version: 8.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: raphael.kubo.da.costa at intel dot com
  Target Milestone: ---

(This is a reduction from a GCC + Chromium build issue)

Building the following excerpt with -std=gnu++14 causes GCC to fail, while
MSVC, clang and ICC work fine:

struct S {
  template <class U>
  constexpr operator U() const {
    return static_cast<U>(42);
  }
};

void frob() {
  new char[S()];
}

x.cc: In function ‘void frob()’:
x.cc:9:14: error: default type conversion can't deduce template argument for
‘template<class U> constexpr S::operator U() const’                             
   new char[S()];
              ^

C++14 says in 8.3.4 Arrays that "If the constant-expression (5.20) is present,
it shall be a converted constant expression of type std::size_t and its value
shall be greater than zero", so I was expecting `new char[S()]' to end up
invoking S::operator size_t().