Add AnErr field type

context.go

@@ -26,6 +26,12 @@ func (c Context) Str(key, val string) Context {
 	return c
 }
 
+// AnErr adds the field key with err as a string to the logger context.
+func (c Context) AnErr(key string, err error) Context {
+	c.l.context = appendErrorKey(c.l.context, key, err)
+	return c
+}
+
 // Err adds the field "error" with err as a string to the logger context.
 // To customize the key name, change zerolog.ErrorFieldName.
 func (c Context) Err(err error) Context {

event.go

@@ -116,7 +116,18 @@ func (e *Event) Str(key, val string) *Event {
 	return e
 }
 
+// AnErr adds the field key with err as a string to the *Event context.
+// If err is nil, no field is added.
+func (e *Event) AnErr(key string, err error) *Event {
+	if !e.enabled {
+		return e
+	}
+	e.buf = appendErrorKey(e.buf, key, err)
+	return e
+}
+
 // Err adds the field "error" with err as a string to the *Event context.
+// If err is nil, no field is added.
 // To customize the key name, change zerolog.ErrorFieldName.
 func (e *Event) Err(err error) *Event {
 	if !e.enabled {

field.go

@@ -19,8 +19,15 @@ func appendString(dst []byte, key, val string) []byte {
 	return appendJSONString(appendKey(dst, key), val)
 }
 
+func appendErrorKey(dst []byte, key string, err error) []byte {
+	if err == nil {
+		return dst
+	}
+	return appendJSONString(appendKey(dst, key), err.Error())
+}
+
 func appendError(dst []byte, err error) []byte {
-	return appendJSONString(appendKey(dst, ErrorFieldName), err.Error())
+	return appendErrorKey(dst, ErrorFieldName, err)
 }
 
 func appendBool(dst []byte, key string, val bool) []byte {

log_test.go

@@ -76,6 +76,7 @@ func TestWith(t *testing.T) {
 	out := &bytes.Buffer{}
 	log := New(out).With().
 		Str("foo", "bar").
+		AnErr("some_err", nil).
 		Err(errors.New("some error")).
 		Bool("bool", true).
 		Int("int", 1).
@@ -103,6 +104,7 @@ func TestFields(t *testing.T) {
 	log := New(out)
 	log.Log().
 		Str("foo", "bar").
+		AnErr("some_err", nil).
 		Err(errors.New("some error")).
 		Bool("bool", true).
 		Int("int", 1).
@@ -129,6 +131,7 @@ func TestFieldsDisabled(t *testing.T) {
 	log := New(out).Level(InfoLevel)
 	log.Debug().
 		Str("foo", "bar").
+		AnErr("some_err", nil).
 		Err(errors.New("some error")).
 		Bool("bool", true).
 		Int("int", 1).