x/tools/cmd/goimports: does not handle package unsafe properly

[pborman]

Please answer these questions before submitting your issue. Thanks!

I believe goimports does not automatically include package unsafe even if referenced in the source, which is fine, but when package unsafe is imported it can confuse goimports and produces syntactically correct, but unexpected output, such as:

import (
    "reflect"
    "unsafe"
)
import "fmt"

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

go version go1.6 linux/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GORACE=""
GOROOT="/usr/lib/google-golang"
GOTOOLDIR="/usr/lib/google-golang/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -gno-record-gcc-switches -fdebug-prefix-map=/tmp/go-build262021310=/tmp/go-build"
CXX="g++"
CGO_ENABLED="1"

1. What did you do?

Ran goimports on the source code http://play.golang.org/p/Ppc325UINU

package code

import "unsafe"
import "fmt"

var _ = fmt.Print
var _ = unsafe.Sizeof
var _ = reflect.Value

1. What did you expect to see?

http://play.golang.org/p/ySR9QrdVlp

package code

import (
    "fmt"
    "reflect"
    "unsafe"
)

var _ = fmt.Print
var _ = unsafe.Sizeof
var _ = reflect.Value

1. What did you see instead?

http://play.golang.org/p/i49dfImPxA

package code

import (
    "reflect"
    "unsafe"
)
import "fmt"

var _ = fmt.Print
var _ = unsafe.Sizeof
var _ = reflect.Value

[ianlancetaylor]

CC @bradfitz

[davidrjenni]

This is a duplicate of #14075.
There is a fix waiting for review: https://golang.org/cl/19828.