rb_id_serial_to_id: return unregistered ID as an internal ID

```ruby
def foo(*); ->{ super }; end
```

This code makes anonymous parameters which is not registered as an
ID.  The problem is that when Ractors try to scan `getlocal`
instructions, it puts the Symbol corresponding to the parameter
in to a hash.  Since it is not registered, we end up with a
strange exception.  This commit wraps the unregistered ID in an
internal ID so that we get the same exception for `...` as `*`.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: John Hawthorn <john@hawthorn.email>

1 files changed, 2 insertions, 1 deletions

diff --git a/symbol.c b/symbol.c
index 1b2a77c7c4..79ec4de502 100644
--- a/symbol.c
+++ b/symbol.c
@@ -486,7 +486,8 @@ rb_id_serial_to_id(rb_id_serial_t num)
 {
     if (is_notop_id((ID)num)) {
         VALUE sym = get_id_serial_entry(num, 0, ID_ENTRY_SYM);
-	return SYM2ID(sym);
+	if (sym) return SYM2ID(sym);
+	return ((ID)num << ID_SCOPE_SHIFT) | ID_INTERNAL | ID_STATIC_SYM;
     }
     else {
 	return (ID)num;