<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/83979>83979</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang rejects call to base class member function inside requires inside constexpr if using scope resolution operatot
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          ranaanoop
      </td>
    </tr>
</table>

<pre>
    The following program is rejected by clang :[Demo](https://godbolt.org/z/34ra7aM1s)
```
#include<type_traits>
 
template<typename T>
struct AlwaysFalse : public std::false_type {};

struct B
{
  template<typename S>
  void foo(){}
};

template <typename T,typename S>
struct A:T
{
 auto foo(){
    if constexpr (requires{T::template foo<S>();})
 return 1;
    else
       static_assert(AlwaysFalse<A>::value,
 "foo is not implemented.");
  }
};

int main()
{
A<B,double> a;
a.foo();
}
```

Clang says:
```
<source>:19:22: error: static assertion failed due to requirement 'AlwaysFalse<A<B, double>>::value': foo is not implemented.
 19 |        static_assert(AlwaysFalse<A>::value,
      | ^~~~~~~~~~~~~~~~~~~~~
<source>:27:3: note: in instantiation of member function 'A<B, double>::foo' requested here
   27 | a.foo();
      | ^
1 error generated.
Compiler returned: 1
```

---

Note program work if we change constexpr if to `if constexpr (requires(T t){t. template foo<S>();})`. [Demo](https://godbolt.org/z/jKGfenq1o)
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJykVcGSozYQ_Zrm0jUukIwxBw42HueQSi7xfUpAY2sjJFYSM3EO-faUANtjr3crqaVcBgnx-vXrfpJwTh41UQHpFtJdJAZ_MrawQguhjemjyjTn4nAibI1S5kPqI_bWHK3oUDq09IVqTw1WZ6yV0EcEvoF0u6POQLoDtj5537swyfbA9kfTVEb5hbFHYPu_ge350opM_JY4YDnEO4g3sIrn3zRkXOpaDQ0BL_25pzdvhfQO-Ou0AKebp65Xwl9WadERHq6LnLdD7XGjPsTZ7YVyFJhiP1RK1uh8EyjyTRvevIXvEbItZDvg25nGZ5jLXDY_ID6L_seNIr4b2WBrDLB1SHTCnkEeg1yw8D4V9gz5khfwzeGRlBi8uY85k0GULdZGO09_9RaBrS19HaQlB9n2MClxJREAeDlGnHD4yP1SLbTkB6sxuSYR8Ek5uo0Q0XnhZf0mnCPrga0_FQJ4uQnoY9h3oQYCVl5Ky1hrTOg0bTzKrlfUkfbULICxmcwc5geCSu2xE1LPCdzLtAFeboGVjRkqRcBfUVw_F4ubfFfIa5yHPh3_y9EETpzHnn-6jpfODLamKeckB75hLDQjWWtseJjEwkksaTS2QipqsBkIvcG5WEEIBJZ9I-WYDl7zedQ2CyG-p-okZpIjZCX-XO3GK8BA-vrPk-upHCM7HhhqE9y0QalRaueF9lKMYpgWO-oqstgOuh6nggpP8h4dHQqYjZqRCzvVieytNVk2MnxW5zv-01QylQiPpMmKm16l6XqpyM5eoLCZYPKDLnl5efk8_N14uu6qH8b-Gfz5QVifhD7SJ6fKNtQfVvF3_cvWB_ST2_0C_4OJV_EC_9eG_eXXX1rSXxMDLI-agjc5z0VERZLF-YrH6TKJTkXF1ytGS5asqK1rShOxyhk19TLmzarlbSQLFrNlzOM0zhljyWJZ89WapQ1PWMrStoVlTJ2QaqHUexfCR9K5gYo1z7M8UqIi5cZDi7Hx4An7QbqLbBHWv1TD0cEyVtJ5d0Pw0isqJotOJ5fDWigVRK2Eo3CEOfdNd0ntZEMX27nL-K4sgwsno6tNHxY6o4apV_vQKMZHg1XFg7LSn4ZqUZsO2D5QnG8vvTWBGrD9mLEDth-T_jcAAP__IQBHTg">