cmd/compile: `internal compiler error: getinarg: not a func` when returning invalid interface

[dominikh]

Input:

package bug

type I interface {
    int
}

func New() I {
    return struct{}{}
}

Output:

dominikh-pc /tmp $ go build foo.go
# command-line-arguments
./foo.go:4: interface contains embedded non-interface int
./foo.go:8: internal compiler error: getinarg: not a func int

Expected output:
No internal compiler error.

Version:
go version devel +5ee5528 Thu May 28 12:04:35 2015 +0000 linux/amd64

Also happens with Go 1.4.

[anthonycanino1]

I spent some time narrowing down why this bug happens and would like to provide a fix with some guidance (would by my first contribution).

I believe the issue is in the subr.go:implements function. The bad embedded type 'int' is flagged as broke in dcl.go:interfacefield but is still checked to see if it is implemented in the code below. int obviously isn't a method, which eventually errors in methodfunc/getinarg.

for im := iface.Type; im != nil; im = im.Down {
  imtype = methodfunc(im.Type, nil)
  tm = ifacelookdot(im.Sym, t, &followptr, 0)

A "fix" is to skip over the check if im.Broke == 1, but I am not sure if that is correct. Any advice on the desired way to handle this?

[gopherbot]

CL https://golang.org/cl/13747 mentions this issue.