https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96411
Bug ID: 96411
Summary: erroneous "trait used in its own initializer" error
when using concepts in a requirement
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Reduced from StackOverflow (https://stackoverflow.com/q/63202619/2069064):
template <typename> constexpr bool trait = true;
template <typename T> concept C = trait<T>;
void f(auto) {
[]<typename T>(){
requires { C<T>; };
};
}
int main() { f(42); }
This fails on gcc 10.2 with:
<source>: In instantiation of 'void f(auto:1) [with auto:1 = int]':
<source>:10:18: required from here
<source>:2:31: required by the constraints of 'template<class T> concept C'
<source>:2:35: error: the value of 'trait<T>' is not usable in a constant
expression
2 | template <typename T> concept C = trait<T>;
| ^~~~~~~~
<source>:1:36: note: 'trait<T>' used in its own initializer
1 | template <typename> constexpr bool trait = true;
| ^~~~~
Compiler returned: 1
But trait<T> isn't used in its own initializer, and trait<T> is certainly
usable in a constant expression.
