[clang++] unexpected error: substitution into constraint expression resulted in a non-constant expression #93327
Description
Consider the following piece of C++20 code:
template<typename> struct property;
template<typename Derived>
struct B {
void doit() {
[]<typename R, typename... Args>(R (Derived::*)(Args...)) {
constexpr bool x = requires {
requires property<R>::value == 3;
};
} (&Derived::f);
}
};
struct A : B<A> {
int f();
};
void test() {
A{}.doit();
}clang++ emits the following diagnostics:
<source>:8:26: error: substitution into constraint expression resulted in a non-constant expression
8 | requires property<R>::value == 3;
| ^~~~~~~~~~~~~~~~~~~~~~~
<source>:8:26: note: while checking the satisfaction of nested requirement requested here
8 | requires property<R>::value == 3;
| ^~~~~~~~~~~~~~~~~~~~~~~
<source>:8:26: note: in instantiation of requirement here
8 | requires property<R>::value == 3;
| ^~~~~~~~~~~~~~~~~~~~~~~
<source>:8:26: note: while checking the satisfaction of nested requirement requested here
8 | requires property<R>::value == 3;
| ^~~~~~~~~~~~~~~~~~~~~~~
<source>:6:67: note: while substituting into a lambda expression here
6 | []<typename R, typename... Args>(R (Derived::*)(Args...)) {
| ^
<source>:20:9: note: in instantiation of member function 'B<A>::doit' requested here
20 | A{}.doit();
| ^
<source>:8:45: note: non-literal type '<dependent type>' cannot be used in a constant expression
8 | requires property<R>::value == 3;
| ^
however gcc, msvc, and edg compile it just fine: https://gcc.godbolt.org/z/7rjG4T6o4