go/types: ObjectString: remove only 1 Alias for "type A = RHS"
As we migrate towards materialized Alias types, the ObjectString
for a type A such as
type A = B
type B = int
should be "type A = B", removing exactly one Alias constructor
from the type of A. (The previous behavior was "type A = int".)
I suspect the existing Alias.{Unalias,Underlying} API is
inadequate and that we will need an Alias.RHS accessor that
removes exactly one Alias. Other clients such as the import/
export packages will need it, because aliases are not
isomorphic to defined types, in which, given
type A B
type B int
the Underlying of A is indeed int. See #66559.
Change-Id: I11a4aacbe6dbeeafc3aee31b3c096296b5970cd8
Reviewed-on: https://go-review.googlesource.com/c/go/+/574716
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>