Don't depend on os/user anymore, which requires cgo

configfile.go

+package main
+
+// ConfigFile returns the default path to the configuration file. On
+// Unix-like systems this is the ".packerconfig" file in the home directory.
+// On Windows, this is the "packer.config" file in the application data
+// directory.
+func ConfigFile() (string, error) {
+	return configFile()
+}

configfile_unix.go

+// +build darwin freebsd linux netbsd openbsd
+
+package main
+
+import (
+	"bytes"
+	"errors"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+func configFile() (string, error) {
+	dir, err := configDir()
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(dir, ".packerconfig"), nil
+}
+
+func configDir() (string, error) {
+	// First prefer the HOME environmental variable
+	if home := os.Getenv("HOME"); home != "" {
+		log.Printf("Detected home directory from env var: %s", home)
+		return home, nil
+	}
+
+	// If that fails, try the shell
+	var stdout bytes.Buffer
+	cmd := exec.Command("sh", "-c", "eval echo ~$USER")
+	cmd.Stdout = &stdout
+	if err := cmd.Run(); err != nil {
+		return "", err
+	}
+
+	result := strings.TrimSpace(stdout.String())
+	if result == "" {
+		return "", errors.New("blank output")
+	}
+
+	return result, nil
+}

configfile_windows.go

+// +build windows
+
+package main
+
+import (
+	"path/filepath"
+	"syscall"
+	"unsafe"
+)
+
+var (
+	shell         = syscall.MustLoadDLL("Shell32.dll")
+	getFolderPath = shell.MustFindProc("SHGetFolderPathW")
+)
+
+const CSIDL_APPDATA = 26
+
+func configFile() (string, error) {
+	dir, err := configDir()
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(dir, "packer.config"), nil
+}
+
+func configDir() (string, error) {
+	b := make([]uint16, syscall.MAX_PATH)
+
+	// See: http://msdn.microsoft.com/en-us/library/windows/desktop/bb762181(v=vs.85).aspx
+	r, _, err := getFolderPath.Call(0, CSIDL_APPDATA, 0, 0, uintptr(unsafe.Pointer(&b[0])))
+	if uint32(r) != 0 {
+		return "", err
+	}
+
+	return syscall.UTF16ToString(b), nil
+}

packer.go

@@ -9,8 +9,6 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
-	"os/user"
-	"path/filepath"
 	"runtime"
 )
 
@@ -82,19 +80,23 @@ func loadConfig() (*config, error) {
 	}
 
 	mustExist := true
-	configFile := os.Getenv("PACKER_CONFIG")
-	if configFile == "" {
-		u, err := user.Current()
+	configFilePath := os.Getenv("PACKER_CONFIG")
+	if configFilePath == "" {
+		var err error
+		configFilePath, err = configFile()
+		mustExist = false
+
 		if err != nil {
-			return nil, err
+			log.Printf("Error detecing default config file path: %s", err)
+		}
 	}
 
-		configFile = filepath.Join(u.HomeDir, ".packerconfig")
-		mustExist = false
+	if configFilePath == "" {
+		return &config, nil
 	}
 
-	log.Printf("Attempting to open config file: %s", configFile)
-	f, err := os.Open(configFile)
+	log.Printf("Attempting to open config file: %s", configFilePath)
+	f, err := os.Open(configFilePath)
 	if err != nil {
 		if !os.IsNotExist(err) {
 			return nil, err