System.Text.Json contract customization: not possible to enable deserialization in properties marked JsonIgnoreCondition.Always #71886
Description
Consider the following test:
[Fact]
public static void CanEnableDeserializationOnAlwaysIgnoreProperty()
{
var options = new JsonSerializerOptions
{
TypeInfoResolver = new DefaultJsonTypeInfoResolver
{
Modifiers =
{
jsonTypeInfo =>
{
if (jsonTypeInfo.Type != typeof(ClassWithJsonIgnoreAlwaysProperty))
{
return;
}
JsonPropertyInfo jsonPropertyInfo = jsonTypeInfo.Properties[0];
jsonPropertyInfo.Set = (obj, value) => ((ClassWithJsonIgnoreAlwaysProperty)obj).Value = (int)value;
}
}
}
};
ClassWithJsonIgnoreAlwaysProperty value = JsonSerializer.Deserialize<ClassWithJsonIgnoreAlwaysProperty>("""{"Value":42}""", options);
Assert.Equal(42, value.Value);
}
public class ClassWithJsonIgnoreAlwaysProperty
{
[JsonIgnore]
public int Value { get; set; }
}This happens because the DetermineSerializationCapabilities method will mark the property as non-serializable/deserializable based on the initial value of JsonIgnoreCondition. JsonIgnoreCondition is not user-settable so no user modification on the contract model can prevent this.
I would recommend we change this so that all logic in DetermineSerializationCapabilities is done at initialization time and can be modified by users. Additionally, I propose we introduce a ShouldDeserialize method to JsonPropertyInfo:
public partial class JsonPropertyInfo
{
public Func<object, object?, bool> ShouldSerialize { get; set; }
+ public Func<object, object?, bool> ShouldDeserialize { get; set; }
}The two delegates would allow mapping all possible JsonIgnoreCondition configurations to these two delegates and not require nulling out the Get and Set delegates as we currently do for JsonIgnoreCondition.Always. Contract customization in Json.NET also includes a ShouldDeserialize delegate complementing ShouldSerialize so we should be following a similar approach in System.Text.Json.