proposal: add omitnull option

[Qhesz]

Current behaviour

Given the following types:

type container struct {
    A optInt `json:"a"`
}

type optInt struct {
    Present bool
    Value int
}

func (o *optInt) UnmarshalJSON(b []byte) error { ... }

func (o optInt) MarshalJSON() ([]byte, error) {
    // Returns "null" if not present
    ...
}

The input json {} would be marshalled back out as {"a":null}

Proposed optional behaviour:

With an extra option omitnull:

type container struct {
    A optInt `json:"a,omitnull"`
}

The input json {} would be marshalled back out as {}

In general, omitnull would mean that if the tagged field's value marshals to the json null value, then omit the field entirely from the output.

Reason I don't want to use *int

I want to maintain == on structs, and adding a pointer inside my container struct means I can no longer use ==.

Generalising

This would provide a mechanism for omitting any nested struct, which is the only (?) type not covered by the existing omitempty option.

[agnivade]

Hello @Qhesz, thanks for creating this proposal. This is a duplicate of #11939. I will close this in favor of that one. Please feel free to subscribe to that one. Thank you.