public delegate void Delegate();

// this compiles
void syncFunc( Delegate cb )
{
        cb();
}

// this not
async void asyncFunc( Delegate cb )
{
        cb();
}

void main()
{
}

============================================
** (valac:24379): CRITICAL **: vala_data_type_get_value_owned: assertion `self != NULL' failed
/local/pkg/vala/test/asyncdelegateparam.vala.c: In function 'asyncFunc_data_free':
/local/pkg/vala/test/asyncdelegateparam.vala.c:40: error: 'asyncFuncData' has no member named 'cb_target_destroy_notify'
/local/pkg/vala/test/asyncdelegateparam.vala.c:40: error: 'asyncFuncData' has no member named 'cb_target_destroy_notify'
/local/pkg/vala/test/asyncdelegateparam.vala.c:43: error: 'asyncFuncData' has no member named 'cb_target_destroy_notify'
error: cc exited with status 256
Compilation failed: 1 error(s), 2 warning(s)