Adding a new interface instead of updating FieldLogger

logrus.go

@@ -168,8 +168,6 @@ type FieldLogger interface {
 	Fatalln(args ...interface{})
 	Panicln(args ...interface{})
 
-	SetLevel(level Level)
-	IsLevelEnabled(level Level) bool
 	// IsDebugEnabled() bool
 	// IsInfoEnabled() bool
 	// IsWarnEnabled() bool
@@ -178,6 +176,12 @@ type FieldLogger interface {
 	// IsPanicEnabled() bool
 }
 
+type Ext2FieldLogger interface {
+	FieldLogger
+	SetLevel(level Level)
+	IsLevelEnabled(level Level) bool
+}
+
 // Ext1FieldLogger (the first extension to FieldLogger) is superfluous, it is
 // here for consistancy. Do not use. Use Logger or Entry instead.
 type Ext1FieldLogger interface {

logrus_test.go

@@ -631,14 +631,23 @@ func TestLogrusInterfaces(t *testing.T) {
 		b := l.WithField("key", "value")
 		b.Debug("Test")
 	}
+
+	fn2 := func(xl Ext2FieldLogger) {
+		var l FieldLogger = xl
+		b := l.WithField("key", "value")
+		b.Debug("Test")
+	}
+
 	// test logger
 	logger := New()
 	logger.Out = &buffer
 	fn(logger)
+	fn2(logger)
 
 	// test Entry
 	e := logger.WithField("another", "value")
 	fn(e)
+	fn2(e)
 }
 
 // Implements io.Writer using channels for synchronization, so we can wait on