cmd/compile: method call on interface panics, but works on the contained struct #24547
Description
What version of Go are you using (go version)?
go version go1.10 linux/amd64
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/a/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/a"
GORACE=""
GOROOT="/home/a/go"
GOTMPDIR=""
GOTOOLDIR="/home/a/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build961933609=/tmp/go-build"
What did you do?
https://play.golang.org/p/TjVzZGtL8zz
package main
import (
"bytes"
"fmt"
"log"
)
type mystruct struct {
f int
}
func (t mystruct) String() string {
return "foo"
}
func main() {
type deep struct {
mystruct
}
s := struct {
deep
*bytes.Buffer
}{
deep{},
bytes.NewBufferString("TEST"),
}
log.Print(s.String()) // ok
var i fmt.Stringer = s
log.Print(i.String) // ok
log.Print(i.String()) // panic
}
What did you expect to see?
2018/03/27 03:04:27 TEST
2018/03/27 03:04:27 0x48dc70
2018/03/27 03:04:27 TEST
What did you see instead?
2018/03/27 03:04:27 TEST
2018/03/27 03:04:27 0x48dc70
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x0]
goroutine 1 [running]:
main.main()
/tmp/test.go:31 +0x25c
Are my expectations correct? I have reread the Struct types and the Selectors paragraphs of the specs but I can't find an explanation for the panic, I hope I haven't overlooked something obvious.
It seems related to the method collision (at different depths) and some specific combination of pointers and values.