[Freeciv-Dev] Unsafe assertions. (PR#864)

[Gaute B Strokkenes <gs234@xxxxxxxxx>]

The recent discussion about normalize_map_pos() has brought to my
attention a potential problem with the way we use it:

donald:~/freeciv$ grep --binary-files without-match -r assert.*norm *
client/goto.c:  assert(normalize_map_pos(&x, &y));
client/goto.c:  assert(normalize_map_pos(&x1, &y1));
client/goto.c:      assert(normalize_map_pos(&new_x, &new_y));
client/goto.c:  assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:  assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:    assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:    assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:    assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:       assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:       assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-gtk/mapview.c:  assert(normalize_map_pos(&x, &y));
client/gui-mui/graphics.c:  assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-mui/graphics.c:  assert(normalize_map_pos(&x, &y));
client/gui-mui/mapclass.c:        assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-mui/mapclass.c:        assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-mui/mapclass.c:          assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-mui/mapclass.c:              assert(normalize_map_pos(&dest_x, 
&dest_y));
client/gui-mui/mapclass.c:              assert(normalize_map_pos(&dest_x, 
&dest_y));
client/gui-xaw/mapview.c:  assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-xaw/mapview.c:  assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-xaw/mapview.c:      assert(normalize_map_pos(&dest_x, &dest_y));
client/gui-xaw/mapview.c:      assert(normalize_map_pos(&dest_x, &dest_y));
common/map.c:  assert(normalize_map_pos(&x, &y));
common/map.c:  assert(normalize_map_pos(x, y));
server/citytools.c:    assert(normalize_map_pos(&map_x, &map_y));
server/mapgen.c:        assert(normalize_map_pos(&map_x, &map_y));

The reason this is dangerous is that normaliz_map_pos() will sometimes
change the value of x.  If we compile with NDEBUG, this does not
happen, and a crash may occur.

I think we should changes these uses to is_real_tile() instead, and
use normalize_map_pos() explicitly if we rely on the value of x being
normalised afterwards.

-- 
Big Gaute                               http://www.srcf.ucam.org/~gs234/
I appoint you ambassador to Fantasy Island!!!