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

go version go1.7.3 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/meomap/testlinter"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/6f/tq_z_9xs71vg9wlv5yg8g_lm0000gn/T/go-build230941075=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

I run go tool vet --shadow on top repository of 3 packages, each has a main.go file:

// `a/main.go`
package main

var foo error

func main() {
}

// `b/main.go`
package main

import (
        "errors"
        "fmt"
)

func main() {
        foo := errors.New("meomeo")
        fmt.Println(foo)
}

// `c/main.go`
package main

import "errors"

type foo error

func newFoo(msg string) foo {
        return foo(errors.New(msg))
}

func main() {
}

vet command

$ go tool vet --shadow a/main.go b/main.go c/main.go 

What did you expect to see?

no vet error, same output as

$ go tool vet --shadow .

What did you see instead?

b/main.go:9: declaration of "foo" shadows declaration at a/main.go:3

but when I run same vet on a/main.go and b/main.go only, no vet error

$ go tool vet --shadow a/main.go b/main.go 

or change order of arguments input, no vet error

$ go tool vet --shadow c/main.go b/main.go a/main.go