fmtfoo.go

// src/fmt/foo.go
package fmt

import "internal/foo"

var _ = foo.Foo{}

foo.go

// src/internal/foo/foo.go
package foo

type Foo struct{}

output

$ go build -v -a fmt
runtime
internal/foo
errors
sync/atomic
math
unicode/utf8
sync
io
syscall
strconv
time
reflect
os
fmt
$ echo $?
0