go: Use of internal package ... is not allowed

Please answer these questions before submitting your issue. Thanks!

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

go 1.11rc1

Does this issue reproduce with the latest release?

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

win 10x64 set GOARCH=amd64 set GOBIN=d:\soft\bin set GOCACHE=C:\Users\Alexander.go\cache set GOEXE=.exe set GOFLAGS= set GOHOSTARCH=amd64 set GOHOSTOS=windows set GOOS=windows set GOPATH=C:\Users\Alexander.go\go set GOPROXY= set GORACE= set GOROOT=d:\soft\go set GOTMPDIR= set GOTOOLDIR=d:\soft\go\pkg\tool\windows_amd64 set GCCGO=gccgo set CC=gcc set CXX=g++ set CGO_ENABLED=1 set GOMOD=D:\Dev\go\scratch\go.mod set CGO_CFLAGS=-g -O2 set CGO_CPPFLAGS= set CGO_CXXFLAGS=-g -O2 set CGO_FFLAGS=-g -O2 set CGO_LDFLAGS=-g -O2 set PKG_CONFIG=pkg-config set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\ALEXAN~1\AppData\Local\Temp\go-build973572782=/tmp/go-build -gno-record-gcc-switches

What did you do?

scratch/go.mod

module scratch

scratch/main.go

package main

import "scratch/internal"

func main() {
	internal.F()
}

scratch/internal/f.go

package internal

func F() {}

go build main.go

What did you expect to see?

Compilation success

What did you see instead?

main.go:3:8 use of internal package scratch/internal not allowed