utils.go: added function ExpandPath

utils.go

@@ -6,7 +6,11 @@ package expr
 
 import (
 	"fmt"
+	"os"
+	"os/user"
+	"path"
 	"reflect"
+	"strings"
 )
 
 func IsString(v any) (ok bool) {
@@ -221,3 +225,37 @@ func ForAll[T, V any](ts []T, fn func(T) V) []V {
 	}
 	return result
 }
+
+func ExpandPath(sourcePath string) (expandedPath string, err error) {
+	for expandedPath = os.ExpandEnv(sourcePath); expandedPath != sourcePath; expandedPath = os.ExpandEnv(sourcePath) {
+		sourcePath = expandedPath
+	}
+
+	if strings.HasPrefix(sourcePath, "~") {
+		var home, userName, remainder string
+
+		slashPos := strings.IndexRune(sourcePath, '/')
+		if slashPos > 0 {
+			userName = sourcePath[1:slashPos]
+			remainder = sourcePath[slashPos:]
+		} else {
+			userName = sourcePath[1:]
+		}
+
+		if len(userName) == 0 {
+			home, err = os.UserHomeDir()
+			if err != nil {
+				return
+			}
+		} else {
+			var userInfo *user.User
+			userInfo, err = user.Lookup(userName)
+			if err != nil {
+				return
+			}
+			home = userInfo.HomeDir
+		}
+		expandedPath = path.Join(home, remainder)
+	}
+	return
+}