go/types, types2: add missing Named.unpack call in Checker.hasVarSize
CL 734980 swapped use of Type.Underlying() in Checker.hasVarSize for
traversal of Named.fromRHS. It forgot to call Named.unpack() before
inspecting Named.fromRHS, allowing access of unexpanded instantiated
types.
These unexpanded instantiated types are then mistakenly marked as having
fixed size, which fails assertions downstream. This change adds the
missing Named.unpack() call and swaps direct access of Named.fromRHS for
Named.rhs(), which verifies such access in debug mode.
Fixes #77382
Change-Id: I324bbbbf790f8b09e95902ebe67f775483f88417
Reviewed-on: https://go-review.googlesource.com/c/go/+/740620 Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>