How to remove all contents of a directory using Golang?

I'm new to Go and can't seem to find a way to delete all the contents of a directory when I don't know the contents.

I've tried:

os.RemoveAll("/tmp/*")
os.Remove("/tmp/*")

but get remove *: no such file or directory or invalid argument.

And of course if you do:

os.RemoveAll("/tmp/")

it deletes the tmp directory as well. Which is not what I want.

Write a simple RemoveContents function. For example,

package main

import (
    "fmt"
    "os"
    "path/filepath"
    "strings"
)

func RemoveContents(dir string) error {
    d, err := os.Open(dir)
    if err != nil {
        return err
    }
    defer d.Close()
    names, err := d.Readdirnames(-1)
    if err != nil {
        return err
    }
    for _, name := range names {
        err = os.RemoveAll(filepath.Join(dir, name))
        if err != nil {
            return err
        }
    }
    return nil
}

func main() {
    dir := strings.TrimSuffix(filepath.Base(os.Args[0]), filepath.Ext(os.Args[0]))
    dir = filepath.Join(os.TempDir(), dir)
    dirs := filepath.Join(dir, `tmpdir`)
    err := os.MkdirAll(dirs, 0777)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    file := filepath.Join(dir, `tmpfile`)
    f, err := os.Create(file)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    f.Close()
    file = filepath.Join(dirs, `tmpfile`)
    f, err = os.Create(file)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    f.Close()

    err = RemoveContents(dir)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
}

Stack Overflow Q#33450980, score: 51