[Bug c++/85809] SFINAE code compiles that shouldn't be able to compile.

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85809

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |9.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed in GCC 9.0.
In file included from <source>:1:
/opt/compiler-explorer/gcc-9.1.0/include/c++/9.1.0/type_traits: In substitution
of 'template<bool _Cond, class _Tp> using enable_if_t = typename
std::enable_if::type [with bool _Cond = (0 == 1); _Tp = float]':
<source>:20:10:   required from 'class MyClass<FOO>'
<source>:27:26:   required from here
/opt/compiler-explorer/gcc-9.1.0/include/c++/9.1.0/type_traits:2426:11: error:
no type named 'type' in 'struct std::enable_if<false, float>'
 2426 |     using enable_if_t = typename enable_if<_Cond, _Tp>::type;
      |           ^~~~~~~~~~~
ASM generation compiler returned: 1

-------------------------

The original testcase:
#include <type_traits>

enum MyEnum
{
    FOO,
    BAR
};

template <MyEnum E>
void do_stuff(std::enable_if_t<E == FOO, float> a) { /*do foo logic*/ }

template <MyEnum E>
void do_stuff(std::enable_if_t<E == BAR, float> a) { /*do bar logic*/ }

template <MyEnum E>
class MyClass
{
public:
    void go(std::enable_if_t<E == MyEnum::FOO, int>) {}
    void go(std::enable_if_t<E == MyEnum::BAR, float>) {}
};

int main()
{
    do_stuff<MyEnum::BAR>(2.f); // Comment this line out and it doesn't compile
anymore.

    MyClass<MyEnum::FOO> q;
    q.go(1);
}