proposal: encoding/json: add ... json tag to spread

[maru44]

I added new json tag.
This can be instead of embedded generics.

As you know, we cannot embed generics to struct.

this is invalid

type bad[T any] struct{
    Name string
    T
}

I want use embed in json, so I added new json tag to spread struct in its parent.

ex)

type good[T any] struct {
    Name string
    Free T `json:"..."`
}

type more struct {
    Age int
    Country string
}

var foo = good[more]{
    Name: "Foo",
    more: more{
        Age: 20,
        Country: "U.S.A",
    },
}

If you encode it in json. It'll be like this.

{"Name": "Foo", "Age": 20, "Country": "U.S.A"}

My PR.

[icholy]

The door isn't closed on allowing embedding type parameters #43621

[DeedleFake]

Anonymous fields can also be manually named, overriding their typical behavior. I think having a way to do the opposite and treat a named field as though it were anonymous makes sense. Even without generics, it would allow you to have a field of an interface type and spread the values to the parent object:

type Example {
  ID int `json:"id"`
  Name string `json:"name"`
  Extra any `json:"..."`
}

[dsnet]

This sounds like a duplicate of #6213.

[ianlancetaylor]

Closing as dup. Please comment if you disagree.