Re: [PATCH] Always create a new value object in valpy_do_cast

[Tom Tromey <tom@tromey.com>]

>>>>> "Hannes" == Hannes Domani via Gdb-patches <gdb-patches@sourceware.org> writes:

Hannes> In case a pretty printer casts a value to the same type, so value_cast()
Hannes> returns the same object again, you get this simplified situation:

Hannes> {
Hannes>   struct value *val = ((value_object *) self)->value;
Hannes>   scoped_value_mark free_values;
Hannes>   res_val = value_cast (type, val); // this returns val
Hannes>   result = value_to_value_object (res_val);
Hannes> }

Hannes> So value_to_value_object() removes a value at or before the free_values
Hannes> marker.

Something seems off about this to me.

value_to_value_object does this:

      val_obj->value = release_value (val).release ();

release_value is like an "incref" but its actual semantics are: if the
value is on all_values, remove it and return it; otherwise incref.  That
way the caller always (1) is assured that the value isn't on all_values,
and (2) always gets a new reference.

So, I would expect that call to have released it from all_values and
therefore it would not be destroyed.

Furthermore, no matter what, I'd expect a gdb.Value to hold an owning
reference to the underlying value, so it still shouldn't be destroyed by
value_free_to_mark.

I'm not doubting there's a bug here, but I don't understand how it comes
about.  Also, I would rather not fix it the way it is done in this
patch, because I think it is preferable for users of values not to have
to know about whether or not a given API might return the same value.

Tom