[Bug c++/126630] New: fold operand not expanded in return-type-requirement of requires expression

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D126630

            Bug ID: 126630
           Summary: fold operand not expanded in return-type-requirement
                    of requires expression
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hanicka at hanicka dot net
  Target Milestone: ---

This behavior is in GCC since GCC 9.

```
template <typename, typename> concept always_true_with =3D true;

template <typename T, typename... Targets> concept bad_convertible_to =3D
(requires (const T & obj) {
    { obj } -> always_true_with<Targets>;
} && ...);
```

This returns error:
```
<source>:3:74: error: operand of fold expression has no unexpanded parameter
packs
    3 | template <typename T, typename... Targets> concept bad_convertible_=
to =3D
(requires (const T & obj) {
      |=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
 ^~~~~~~~~~~~~~~~~~~~~~~~~~
    4 |     { obj } -> always_true_with<Targets>;
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
    5 | } && ...);
      | ~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
```

Expected bahaviour it will fold whole requires-expression over operator &&,
each with different `Targets`. If the `Targets` is inside of the compound
statement, it works as expected.

Compiler Explorer link: https://compiler-explorer.com/z/d1PTc9MEn=