From 271ead0aefd1747c489a83171d77d5eef2723f15 Mon Sep 17 00:00:00 2001
From: Ben Moss <benm@vmware.com>
Date: Wed, 8 Apr 2020 21:53:22 +0000
Subject: [PATCH] Fix how errors are printed

---
 klogr/klogr.go      |  5 +++++
 klogr/klogr_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/klogr/klogr.go b/klogr/klogr.go
index 8e10665c..944cb70a 100644
--- a/klogr/klogr.go
+++ b/klogr/klogr.go
@@ -134,6 +134,11 @@ func flatten(kvList ...interface{}) string {
 }
 
 func pretty(value interface{}) string {
+	if err, ok := value.(error); ok {
+		if _, ok := value.(json.Marshaler); !ok {
+			value = err.Error()
+		}
+	}
 	jb, _ := json.Marshal(value)
 	return string(jb)
 }
diff --git a/klogr/klogr_test.go b/klogr/klogr_test.go
index ce59406b..795eefd1 100644
--- a/klogr/klogr_test.go
+++ b/klogr/klogr_test.go
@@ -2,7 +2,10 @@ package klogr
 
 import (
 	"bytes"
+	"encoding/json"
+	"errors"
 	"flag"
+	"strings"
 	"testing"
 
 	"k8s.io/klog/v2"
@@ -70,6 +73,20 @@ func TestInfo(t *testing.T) {
 			text:          "test",
 			keysAndValues: []interface{}{"akey", "avalue", "akey2"},
 			expectedOutput: ` "msg"="test" "basekey1"="basevar1" "basekey2"=null "akey"="avalue" "akey2"=null
+`,
+		},
+		"should correctly print regular error types": {
+			klogr:         New().V(0),
+			text:          "test",
+			keysAndValues: []interface{}{"err", errors.New("whoops")},
+			expectedOutput: ` "msg"="test"  "err"="whoops"
+`,
+		},
+		"should use MarshalJSON if an error type implements it": {
+			klogr:         New().V(0),
+			text:          "test",
+			keysAndValues: []interface{}{"err", &customErrorJSON{"whoops"}},
+			expectedOutput: ` "msg"="test"  "err"="WHOOPS"
 `,
 		},
 	}
@@ -95,3 +112,15 @@ func TestInfo(t *testing.T) {
 		})
 	}
 }
+
+type customErrorJSON struct {
+	s string
+}
+
+func (e *customErrorJSON) Error() string {
+	return e.s
+}
+
+func (e *customErrorJSON) MarshalJSON() ([]byte, error) {
+	return json.Marshal(strings.ToUpper(e.s))
+}