Code review comment for lp://staging/~vanvugt/mir/parenting-server-api

Alan: Actually yes that's the messy part, but is the lesser evil.

The problem is that surface ID is only meaningful in the upper layer (SessionMediator) where it's a key into the map. Down in the scene::Surface and scene::BasicSurface it's meaningless to mention IDs. So the obvious answer then is don't mention any surface ID in the lower layers (set_parent). You can indeed omit the "int id", but that creates two problems:
  1. query() doesn't work at all, because the surface implementation doesn't known its parent ID.
  2. Any future use of query(mir_surface_attrib_parent) in the upper layers would require bespoke hacks in the SessionMediator (return parent() and linear search for the surface pointer to get the ID).

So the options are either live with issues #1 & #2, or the current design to pass in the surface ID separately for storage in the BasicSurface's attribute list (which costs nothing as the memory is already reserved).

That said, making query() return no useful result looks like it could suffice for now. And it would simplify the interface as you point out. I might try it.