JsonTypeInfo OnDeserialized context for better error propagation

[tyler-boyd]

Hey,

I have code that uses OnDeserialized to perform some validations, picture something like this:

public static void Example(JsonTypeInfo typeInfo)
{
    if (typeInfo.Type != typeof(MyType)) return;
    typeInfo.OnDeserialized = obj => 
    {
        throw new JsonException("test");
    }
}

var options = new JsonSerializerOptions() {
    TypeInfoResolver = new DefaultJsonTypeInfoResolver { Modifiers = { Example } }
};
// JsonSerializer.Deserialize<..>(json, options);

The problem I have is that the JsonException I throw does not contain any information about where in the JSON the object that threw the exception is. When errors happen during JSON parsing, there is a path field like $.array[150].example, but in the OnDeserialized callback there is no way to find out where in the object graph we are.

Is what I'm doing bad? Am I missing a way to give more meaningful error messages? Or is this something that would have to be added to STJ?