https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94141
Bug ID: 94141
Summary: c++20 rewritten operator== recursive call mixing
friend and external operators for template class
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: glisse at gcc dot gnu.org
Target Milestone: ---
(reduced from a user of boost/operators.hpp)
template <typename> class A;
template <typename T> bool operator==(const A<T>&, int) { return false; }
template <typename> class A {
friend bool operator==(int y, const A& x) { return x == y; }
};
int main(){
A<short> q;
q==3;
3==q;
}
$ g++ -std=c++2a a.c -Wall && ./a.out
a.c: In instantiation of 'bool operator==(int, const A<short int>&)':
a.c:10:6: required from here
a.c:5:56: warning: in C++20 this comparison calls the current function
recursively with reversed arguments
5 | friend bool operator==(int y, const A& x) { return x == y; }
| ~~^~~~
zsh: segmentation fault ./a.out
If I make both operators friends, or move both outside, gcc is happy, but in
this mixed case, it doesn't seem to want to use the first operator== and
prefers the rewritten second operator==. Of course removing the second
operator== completely also works.
Clang is fine with this version of the code.
I have trouble parsing the standard wording, but IIRC one of the principles
when adding <=> was that explicitly written functions should have priority over
new, invented ones.
Bug 93807 is the closest I could find.
