package main

import (
    "bytes"
    "fmt"
    "go/format"
)

func main() {
    for _, data := range []string{"\n", "  "} {
        data1, err := format.Source([]byte(data))
        if err != nil {
            panic(err)
        }
        data2, err := format.Source(data1)
        if err != nil {
            panic(err)
        }
        if !bytes.Equal(data1, data2) {
            fmt.Printf("non-idempotent format: %q -> %q -> %q\n", data, data1, data2)
        }
    }
}