encoding/json: rendered empty struct on omitempty

[IGLOU-EU]

What version of Go are you using (go version)?

$ go version
go version go1.20 linux/amd64

What did you do?

Marshal a struct into Json with omitempty.
https://go.dev/play/p/nTyS0p_JP3E

type A struct {
	AA string `json:"aa,omitempty"`
	AB []struct {
		ABA int    `json:"aba,omitempty"`
		ABB string `json:"abb,omitempty"`
	} `json:"ab,omitempty"`
	AC struct {
		ACA int `json:"aca,omitempty"`
	} `json:"ac,omitempty"`
}

func main() {
	a, b := json.Marshal(A{AA: "Hum"})
	fmt.Printf("%s\n%v", a, b)
}

What did you expect to see?

{"aa":"Hum"}

What did you see instead?

{"aa":"Hum","ac":{}}

[zephyrtronium]

See also #11939 and #45669, and tangentially #22480. This is working as currently documented:

The "omitempty" option specifies that the field should be omitted from the encoding if the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array, slice, map, or string.

With respect to omitempty, there is no "empty" value of any struct type.

[IGLOU-EU]

Thank you, that true. I go read their's proposal !