support logr.Marshaler

This is useful for proxy objects that want the actual value to be logged as
something other than a string.

internal/serialize/keyvalues.go

@@ -20,6 +20,8 @@ import (
 	"bytes"
 	"fmt"
 	"strconv"
+
+	"github.com/go-logr/logr"
 )
 
 // WithValues implements LogSink.WithValues. The old key/value pairs are
@@ -118,36 +120,41 @@ func KVListFormat(b *bytes.Buffer, keysAndValues ...interface{}) {
 		} else {
 			b.WriteString(fmt.Sprintf("%s", k))
 		}
+		writeValue(b, v)
+	}
+}
 
-		// The type checks are sorted so that more frequently used ones
-		// come first because that is then faster in the common
-		// cases. In Kubernetes, ObjectRef (a Stringer) is more common
-		// than plain strings
-		// (https://github.com/kubernetes/kubernetes/pull/106594#issuecomment-975526235).
-		switch v := v.(type) {
-		case fmt.Stringer:
-			writeStringValue(b, true, StringerToString(v))
-		case string:
-			writeStringValue(b, true, v)
-		case error:
-			writeStringValue(b, true, ErrorToString(v))
-		case []byte:
-			// In https://github.com/kubernetes/klog/pull/237 it was decided
-			// to format byte slices with "%+q". The advantages of that are:
-			// - readable output if the bytes happen to be printable
-			// - non-printable bytes get represented as unicode escape
-			//   sequences (\uxxxx)
-			//
-			// The downsides are that we cannot use the faster
-			// strconv.Quote here and that multi-line output is not
-			// supported. If developers know that a byte array is
-			// printable and they want multi-line output, they can
-			// convert the value to string before logging it.
-			b.WriteByte('=')
-			b.WriteString(fmt.Sprintf("%+q", v))
-		default:
-			writeStringValue(b, false, fmt.Sprintf("%+v", v))
-		}
+func writeValue(b *bytes.Buffer, v interface{}) {
+	// The type checks are sorted so that more frequently used ones
+	// come first because that is then faster in the common
+	// cases. In Kubernetes, ObjectRef (a Stringer) is more common
+	// than plain strings
+	// (https://github.com/kubernetes/kubernetes/pull/106594#issuecomment-975526235).
+	switch v := v.(type) {
+	case fmt.Stringer:
+		writeStringValue(b, true, StringerToString(v))
+	case string:
+		writeStringValue(b, true, v)
+	case error:
+		writeStringValue(b, true, ErrorToString(v))
+	case logr.Marshaler:
+		writeMarshaler(b, v)
+	case []byte:
+		// In https://github.com/kubernetes/klog/pull/237 it was decided
+		// to format byte slices with "%+q". The advantages of that are:
+		// - readable output if the bytes happen to be printable
+		// - non-printable bytes get represented as unicode escape
+		//   sequences (\uxxxx)
+		//
+		// The downsides are that we cannot use the faster
+		// strconv.Quote here and that multi-line output is not
+		// supported. If developers know that a byte array is
+		// printable and they want multi-line output, they can
+		// convert the value to string before logging it.
+		b.WriteByte('=')
+		b.WriteString(fmt.Sprintf("%+q", v))
+	default:
+		writeStringValue(b, false, fmt.Sprintf("%+v", v))
 	}
 }
 
@@ -175,6 +182,16 @@ func ErrorToString(err error) (ret string) {
 	return
 }
 
+func writeMarshaler(b *bytes.Buffer, v logr.Marshaler) {
+	defer func() {
+		if err := recover(); err != nil {
+			// TODO: update tests. For now, behave as before.
+			writeStringValue(b, false, fmt.Sprintf("%+v", v))
+		}
+	}()
+	writeValue(b, v.MarshalLog())
+}
+
 func writeStringValue(b *bytes.Buffer, quote bool, v string) {
 	data := []byte(v)
 	index := bytes.IndexByte(data, '\n')