add jsonb_set support

[accestfromim]

add jsonb_set support function mentioned in issue #4216

[accestfromim]

I am not sure if I did it right. I'd be glad if I can receive your instruction

[prkbuilds]

LGTM. Types are correctly defined as well the nullability, Great Work!

[weiznich]

Thanks for submitting this PR.

I've found an potential issue with nullability inference that should be fixed. You can use the existing CombinedNullableValue trait for this.

[weiznich]

I'm sorry to bring that up, but the following example won't infer nullablity correctly:

    /// let result = diesel::select(jsonb_set::<Jsonb, Nullable<Array<Nullable<Text>>>, _, _, _>(
    ///         // cannot be json!(null)
    ///         json!([]),
    ///         None,
    ///         json!({"foo": 42})
    ///     )).get_result::<Value>(connection)?;

This is expected to only accept a Option<Value> as return type as the return value will be NULL in this case.

[accestfromim]

Thanks for your kind instuction.
I fixed it by doing this:
before:

fn jsonb_set<
        E: JsonbOrNullableJsonb + SingleValue,
        Arr: TextArrayOrNullableTextArray + SingleValue
    >(base: E, path: Arr, new_value: E) -> E;

after:

fn jsonb_set<
        E: JsonbOrNullableJsonb + SingleValue,
        Arr: TextArrayOrNullableTextArray + CombinedNullableValue<E,Jsonb>
    >(base: E, path: Arr, new_value: E) -> Arr::Out;

Thanks for your instruction again!

[weiznich]

Thanks for the update, looks good now