homedir: revamp

Back in the day os/user package was relied on libc functions to parse
/etc/passwd and /etc/group. This was fixed in Go 1.11 by [1] and
subsequent fixes, so there is no more need to parse /etc/passwd.

This assumes that users know when and how to use osusergo build tag
(since this is not something very new, most are).

It might make sense to note in the changelog / release notes that the
static_build tag is no longer supported, and osusergo tag should be
used instead.

[1] https://go-review.googlesource.com/c/go/+/92456

Updates: da6051a
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

homedir.go

@@ -2,27 +2,24 @@ package dbus
 
 import (
 	"os"
-	"sync"
-)
-
-var (
-	homeDir     string
-	homeDirLock sync.Mutex
+	"os/user"
 )
 
+// Get returns the home directory of the current user, which is usually the
+// value of HOME environment variable. In case it is not set or empty, os/user
+// package is used.
+//
+// If linking statically with cgo enabled against glibc, make sure the
+// osusergo build tag is used.
+//
+// If needing to do nss lookups, do not disable cgo or set osusergo.
 func getHomeDir() string {
-	homeDirLock.Lock()
-	defer homeDirLock.Unlock()
-
+	homeDir := os.Getenv("HOME")
 	if homeDir != "" {
 		return homeDir
 	}
-
-	homeDir = os.Getenv("HOME")
-	if homeDir != "" {
-		return homeDir
+	if u, err := user.Current(); err == nil {
+		return u.HomeDir
 	}
-
-	homeDir = lookupHomeDir()
-	return homeDir
+	return "/"
 }