https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103689
Bug ID: 103689 Summary: Overriding spaceship operator when parent class does not define spaceship operator for itself Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: fchelnokov at gmail dot com Target Milestone: --- The following program is ill-formed: ``` #include <compare> struct A; struct I { virtual std::strong_ordering operator <=>(const A&) const { return std::strong_ordering::equal; } }; struct A : I { virtual std::strong_ordering operator <=>(const A&) const = default; }; int main() { A a; I & i = a; return (i <=> a) == 0; } ``` since I::operator <=>(const I&) const is not defined, so A::operator <=>(const A&) const must be implicitly deleted, and a deleted method cannot override a not deleted method from I. This must be a compilation error (as in Clang). GCC compiles it fine, but issues a linker error ``` undefined reference to `A::operator==(A const&) const' ``` Demo: https://gcc.godbolt.org/z/Geoqdo4T8 Related discussion: https://stackoverflow.com/q/70334766/7325599