Use util.WithPrefix (#9005)

Tiny change to use this helper where we can.

Signed-off-by: Anders Eknert <anders.eknert@apple.com>

internal/file/archive/tarball.go

@@ -7,7 +7,8 @@ import (
 	"encoding/json"
 	"errors"
 	"io"
-	"strings"
+
+	"github.com/open-policy-agent/opa/v1/util"
 )
 
 type TarGzWriter struct {
@@ -62,11 +63,7 @@ func MustWriteTarGz(files [][2]string) *bytes.Buffer {
 	defer tgw.Close()
 
 	for _, file := range files {
-		if !strings.HasPrefix(file[0], "/") {
-			file[0] = "/" + file[0]
-		}
-
-		if err := tgw.WriteFile(file[0], []byte(file[1])); err != nil {
+		if err := tgw.WriteFile(util.WithPrefix(file[0], "/"), []byte(file[1])); err != nil {
 			panic(err)
 		}
 	}

v1/bundle/file.go

@@ -14,6 +14,7 @@ import (
 	"sync"
 
 	"github.com/open-policy-agent/opa/v1/loader/filter"
+	"github.com/open-policy-agent/opa/v1/util"
 
 	"github.com/open-policy-agent/opa/v1/storage"
 )
@@ -193,10 +194,7 @@ func (d *dirLoader) WithFollowSymlinks(followSymlinks bool) DirectoryLoader {
 func formatPath(fileName string, root string, pathFormat PathFormat) string {
 	switch pathFormat {
 	case SlashRooted:
-		if !strings.HasPrefix(fileName, string(filepath.Separator)) {
-			return string(filepath.Separator) + fileName
-		}
-		return fileName
+		return util.WithPrefix(fileName, string(filepath.Separator))
 	case Chrooted:
 		// Trim off the root directory and return path as if chrooted
 		result := strings.TrimPrefix(fileName, filepath.FromSlash(root))
@@ -206,10 +204,7 @@ func formatPath(fileName string, root string, pathFormat PathFormat) string {
 		if root == "." && (filepath.Base(fileName) == ManifestExt || filepath.Base(fileName) == ManifestProtoExt) {
 			result = fileName
 		}
-		if !strings.HasPrefix(result, string(filepath.Separator)) {
-			result = string(filepath.Separator) + result
-		}
-		return result
+		return util.WithPrefix(result, string(filepath.Separator))
 	case Passthrough:
 		fallthrough
 	default: