[Bug c++/121779] [16 Regression] use of operator < with spaceship operator returning int inside a template

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121779

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |15.1.0
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |ice-checking,
                   |                            |ice-on-valid-code
      Known to fail|                            |16.0
   Last reconfirmed|                            |2025-09-04
     Ever confirmed|0                           |1
            Summary|ICE when building ladybird  |[16 Regression] use of
                   |browser: internal compiler  |operator < with spaceship
                   |error: tree check: expected |operator returning int
                   |call_expr, have lt_expr in  |inside a template
                   |build_min_non_dep_op_overlo |
                   |ad, at cp/tree.cc:3733      |
   Target Milestone|---                         |16.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced down further to:
```
struct String {
  int operator<=>(String);
};
template<int>
void f(String a, String b) {
  a < b;
}
```

Confirmed. Only -std=c++20 is needed for the above testcase to get the ICE.