Close file descriptor in FileBackend before reopening it

CHANGELOG.md

@@ -7,3 +7,5 @@
   INFO -> Info, etc.
 - Uncompatible NoopBackend.Level() now returns DefaultLevel instead of Fatal
 - Fix: creates new logger with level DefaultLevel instead of Debug
+- Fix: FileBackend now properly closes the file befor reopening it (fixes a
+  potential file descriptor leak)

backend.go

@@ -89,12 +89,19 @@ func (b *FileBackend) Reopen() error {
 		return nil
 	}
 
-	filename_fd, err := os.OpenFile(b.filepath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
-	if err != nil {
-		return errors.New(fmt.Sprintf("Cannot open log file %s (%s)", b.filepath, err.Error()))
-	} else {
-		b.l = filename_fd
+	if c, ok := b.l.(io.Closer); ok {
+		if err := c.Close(); err != nil {
+			return err
 		}
+	}
+
+	fd, err := os.OpenFile(b.filepath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
+	if err != nil {
+		return fmt.Errorf("Cannot open log file %s: %w", b.filepath, err)
+	}
+
+	b.l = fd
+
 	return nil
 }