go/types: incorrect error message with mutually recursive interfaces

[griesemer]

This is just one example of where the current interface type-checking still goes wrong (this assumes https://golang.org/cl/190258):

package p

type A interface {
	a() interface {
		AB
	}
}

type B interface {
	a() interface {
		AB
	}
}

type AB interface {
	a() interface {
		A
		B
	}
	b() interface {
		A
		B
	}
}

go/types testing reports:

$ go test -run Check$ -files=$HOME/tmp/x.go -errlist
--- FAIL: TestCheck (0.00s)
    check_test.go:271: /Users/gri/tmp/x.go:18:3: duplicate method a
    check_test.go:271: /Users/gri/tmp/x.go:17:3:        other declaration of a
    check_test.go:271: /Users/gri/tmp/x.go:22:3: duplicate method a
    check_test.go:271: /Users/gri/tmp/x.go:21:3:        other declaration of a
FAIL
exit status 1
FAIL    go/types        0.079s

Yet, with the spec change for #6977 (and CL 190258) this should not result in any errors.

(Note that cmd/compile also has trouble with this code if changes https://golang.org/cl/187519 et. al.) are in. The corresponding compiler issue is #6589).

Not urgent as this is a rather esoteric case. But at some point we should rethink type-checking of such mutually recursive data structures.

[mdempsky]

Ughhh.

[gopherbot]

Change https://golang.org/cl/191418 mentions this issue: go/types: postpone interface method type comparison to the end

[gopherbot]

Change https://golang.org/cl/191458 mentions this issue: go/types: process each segment of delayed actions in FIFO order

[gopherbot]

Change https://golang.org/cl/195837 mentions this issue: go/types: make sure interfaces are complete before comparing them