Consolidate config value resolution at top level (#705)

* Consolidate env expansion at top level

* Move handling of deprecated config into resolve method

* Handle template interpolation in resolve method

* Clean up and document resolve function

cmd/backup/script.go

@@ -4,7 +4,6 @@
 package main
 
 import (
-	"bytes"
 	"fmt"
 	"log/slog"
 	"os"
@@ -79,24 +78,6 @@ func (s *script) init() error {
 		return nil
 	})
 	// Register notifications first so they can fire in case of other init errors.
-	if s.c.EmailNotificationRecipient != "" {
-		emailURL := fmt.Sprintf(
-			"smtp://%s:%s@%s:%d/?from=%s&to=%s",
-			s.c.EmailSMTPUsername,
-			s.c.EmailSMTPPassword,
-			s.c.EmailSMTPHost,
-			s.c.EmailSMTPPort,
-			s.c.EmailNotificationSender,
-			s.c.EmailNotificationRecipient,
-		)
-		s.c.NotificationURLs = append(s.c.NotificationURLs, emailURL)
-		s.logger.Warn(
-			"Using EMAIL_* keys for providing notification configuration has been deprecated and will be removed in the next major version.",
-		)
-		s.logger.Warn(
-			"Please use NOTIFICATION_URLS instead. Refer to the README for an upgrade guide.",
-		)
-	}
 
 	hookLevel, ok := hookLevels[s.c.NotificationLevel]
 	if !ok {
@@ -143,30 +124,6 @@ func (s *script) init() error {
 	}
 
 	s.file = path.Join("/tmp", s.c.BackupFilename)
-
-	tmplFileName, tErr := template.New("extension").Parse(s.file)
-	if tErr != nil {
-		return errwrap.Wrap(tErr, "unable to parse backup file extension template")
-	}
-
-	var bf bytes.Buffer
-	if tErr := tmplFileName.Execute(&bf, map[string]string{
-		"Extension": func() string {
-			if s.c.BackupCompression == "none" {
-				return "tar"
-			}
-			return fmt.Sprintf("tar.%s", s.c.BackupCompression)
-		}(),
-	}); tErr != nil {
-		return errwrap.Wrap(tErr, "error executing backup file extension template")
-	}
-	s.file = bf.String()
-
-	if s.c.BackupFilenameExpand {
-		s.file = os.ExpandEnv(s.file)
-		s.c.BackupLatestSymlink = os.ExpandEnv(s.c.BackupLatestSymlink)
-		s.c.BackupPruningPrefix = os.ExpandEnv(s.c.BackupPruningPrefix)
-	}
 	s.file = timeutil.Strftime(&s.stats.StartTime, s.file)
 
 	_, err := os.Stat("/var/run/docker.sock")