cmd/vet: "cannot import, possibly version skew" regression

[somersf]

What version of Go are you using (go version)?

Tested using

$ go version
go version devel +c1d9d1f305 Sun May 27 07:33:08 2018 +0000 darwin/amd64

and

$ go version
go version go1.10.2 darwin/amd64

Does this issue reproduce with the latest release?

go1.10.2 and earlier releases do not fail the go vet check.

What operating system and processor architecture are you using (go env)?

Tested on:

• GOOS=darwin GOARCH=amd64
• GOOS=linux GOARCH=amd64

What did you do?

A recent change on master has caused go vet to report an error (..."cannot import, possibly version skew"...) on code that previously passed with go1.10.2, and go-devel versions until recently.

Multiple packages seem to be required - at least in the example I distilled:

Create $GOPATH/src/issue/a/a.go:

package a

type Entry interface {
        Writable() WritableEntry
}

type WritableEntry interface {
        Entry
}

Create $GOPATH/src/issue/b/b.go:

package b

import "issue/a"

var v a.Entry

Then run:

$ go vet issue/...

What did you expect to see?

go vet should not report any errors.

What did you see instead?

go vet reports:

# issue/b
b/b.go:3:8: could not import issue/a (cannot import, possibly version skew (embedded type is not an interface) - reinstall package)
vet: typecheck failures

Additional information

Bisecting the go project commits since this last passed with go-devel, indicates that the regression appeared with commit c730a93

Author: Robert Griesemer <redacted>
Date:   Wed May 23 16:35:56 2018 -0700

    go/types: permit embedding of non-defined interfaces via alias type names

[meirf]

(I am able to reproduce the vet error on darwin/amd64)

@griesemer

[myitcv]

From a cursory glance, this looks to be because issue/a.Entry is not complete yet, i.e. it's Underlying() is nil. But I've not looked any further than that...

[gopherbot]

Change https://golang.org/cl/115155 mentions this issue: go/types: don't over-eagerly verify embedded interfaces