go/types: don't skip defined types when reporting cycles
The newly introduced "late-stage" cycle detection for types
(https://golang.org/cl/196338/) "skips" named types on the
RHS of a type declaration when reporting a cycle. For instance,
for:
type (
A B
B [10]C
C A
)
the reported cycle is:
illegal cycle in declaration of C
C refers to
C
because the underlying type of C resolves to [10]C (note that
cmd/compile does the same but simply says invalid recursive
type C).
This CL introduces the Named.orig field which always refers
to the RHS type in a type definition (and is never changed).
By using Named.orig rather than Named.underlying for the type
validity check, the cycle as written in the source code is
reported:
illegal cycle in declaration of A
A refers to
B refers to
C refers to
A
Fixes #34771.
Change-Id: I41e260ceb3f9a15da87ffae6a3921bd8280e2ac4
Reviewed-on: https://go-review.googlesource.com/c/go/+/199937
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>