Allow JsonIgnore on classes and structs

[TonyValenti]

Background and Motivation

Today, JsonIgnore can only be specified on properties and fields. This creates a needlessly redundant scenario when JsonIgnore should be applied to all members of a type.

For example, today one must write:

    public class Person {
        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<long> Id { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<string> FirstName { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<string> LastName { get; set; }
        
        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<int> Age { get; set; }
    }

    [JsonConverter(typeof(OptionalJsonConverter))]
    public struct Optional<T>  {
      /* ... */
    }

When it would be much nicer to be able to write:

    public class Person {
        public Optional<long> Id { get; set; }
        public Optional<string> FirstName { get; set; }
        public Optional<string> LastName { get; set; }
        public Optional<int> Age { get; set; }
    }

    [JsonConverter(typeof(OptionalJsonConverter))]
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public struct Optional<T>  {
      /* ... */
    }

Proposed API

[JsonIgnore(Condition = ...)] should be specifiable on a class/struct to indicate that all properties/fields of that type have the specified default JsonIgnore condition.

    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = false)]
    public sealed class JsonIgnoreAttribute : JsonAttribute

Usage Examples

See Above.

Alternative Designs

Today you can specify a global JsonIgnore value using JsonSerializerOptions.DefaultIgnoreCondition however, this is undesirable because it will impact other types you are (de)serializing and not just your target type.

Risks

None. Today JsonIgnore cannot be applied to classes so enabling it will not be a breaking change.

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and Motivation

Today, JsonIgnore can only be specified on properties and fields. This creates a needlessly redundant scenario when JsonIgnore should be applied to all members of a type.

For example, today one must write:

    public record Person {
        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<long> Id { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<string> FirstName { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<string> LastName { get; set; }
        
        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
        public Optional<int> Age { get; set; }
    }

    [JsonConverter(typeof(OptionalJsonConverter))]
    public struct Optional<T>  {
      /* ... */
    }

When it would be much nicer to be able to write:

    public record Person {
        public Optional<long> Id { get; set; }
        public Optional<string> FirstName { get; set; }
        public Optional<string> LastName { get; set; }
        public Optional<int> Age { get; set; }
    }

    [JsonConverter(typeof(OptionalJsonConverter))]
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public struct Optional<T>  {
      /* ... */
    }

Proposed API

[JsonIgnore(Condition = ...)] should be specifiable on a class to indicate that all properties/fields of that class have the specified default JsonIgnore condition.

    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Class, AllowMultiple = false)]
    public sealed class JsonIgnoreAttribute : JsonAttribute

Usage Examples

See Above.

Alternative Designs

Today you can specify a global JsonIgnore value using JsonSerializerOptions.DefaultIgnoreCondition however, this is undesirable because it will impact other types you are (de)serializing and not just your target type.

Risks

None. Today JsonIgnore cannot be applied to classes so enabling it will not be a breaking change.

Author:	TonyValenti
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json, untriaged
Milestone:	-

[TonyValenti]

@steveharter

[eiriktsarpalis]

Related to #50294 and #55781. In #55781 (comment) I sketched a potential API for customizing ignored values (and not just null/default values) on the converter level. Would such an alternative suit your use case?

[eiriktsarpalis]

Closing in favor of #55781 (comment)