Hello,

class Foo
{
        public int bar;
        public signal void sig ();
        public void test ()
        {
                int bar2 = 1;
                sig.connect (() => { bar = 2; bar2 = 2; });
        }

}

"this" in the lambda is owned:
_data1_->self = foo_ref (self);
g_signal_connect_data (self, "sig", (GCallback) __lambda0__foo_sig, block1_data_ref (_data1_), (GClosureNotify) block1_data_unref, 0);

--------------

class Foo
{
        public int bar;
        public signal void sig ();
        public void test ()
        {
                sig.connect (() => { bar = 2; });
        }

}

"this" in the lambda is unowned:
g_signal_connect (self, "sig", (GCallback) __lambda0__foo_sig, self);


--------------

class Foo: Object {
...
}

"this in the lambda is unowned:
g_signal_connect_object (self, "sig", (GCallback) __lambda0__foo_sig, self, 0);

The issue:
It must be either alwas unowned or owned. I think the language assumes "this" is always owned.
If unowned it can lead to crashes when "self" gets unreferenced but the signal is still connected.

Proposal:
Always use g_signal_connect_data like the first case. For what concerns g_signal_connect_object, if using g_signal_connect_data there's no more the need to surround the callback with ref/unref.