When GODEBUG=gotypesalias=1 is set, use an actual Alias type to
represent any, rather than a legacy alias representation. This makes any
consistent with other interface aliases, and will eventually make
obsolete the various workarounds for formatting any as 'any' rather than
'interface{}'.
Since any is a global in the Universe scope, we must hijack Scope.Lookup
to select the correct representation. Of course, this also means that we
can't support type checking concurrently while mutating gotypesalias
(or, in the case of types2, Config.EnableAlias). Some care is taken to
ensure that the type checker panics in the event of this type of misuse.
For now, we must still support the legacy representation of any, and the
existing workarounds that look for a distinguished any pointer. This is
done by ensuring that both representations have the same underlying
pointer, and by updating workarounds to consider Underlying.
Fixes golang/go#66921
Change-Id: I81db7e8e15317b7a6ed3b406545db15a2fc42f57
Reviewed-on: https://go-review.googlesource.com/c/go/+/580355 Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>