TreeTypeMap and MiniPhases have an architectural problem

[felixmulder]

See illustration in #1770

[odersky]

I don't think there are actionable items for this in the foreseeable future. If someone wants to redesign this at some point, we can re-open.

[smarter]

We now always run mini-phases tree transforms with ctx.phase set to be at the group end, so I think this is actually fixed in practice.