The interface_type branch only handled interface embedding and generic
type-set constraints, so the method requirements that make up an
interface's contract were dropped. An interface such as
type Shape interface {
Area() float64
Perimeter() (float64, error)
}
became an empty node - Area and Perimeter never entered the graph, and
nothing could resolve against the interface's method set.
Walk the method_elem children too, mirroring the receiver-method path:
each requirement becomes a .Method() node hung off the interface via a
method edge. Embedding (type_elem) keeps emitting embeds/references, so
the two never blur.
Adds regression coverage: requirements surface as method nodes, an
embedded interface stays a heritage edge, and an interface method and a
concrete struct method of the same name remain distinct nodes.
(cherry picked from commit 739940a42b)
oleksii-tumanov