[API Proposal]: System.Text.Json.Schema: option to disable generating $refs

Start with JsonSchemaExporterOptions and the GetJsonSchemaAsNode entry point mentioned in the issue, then trace where the schema exporter creates $ref nodes. Add the proposed GenerateRefs option and verify that disabling it produces an expanded schema without references for the provided nested dictionary case.

Background and motivation

I apply DataAnnotations attributes (migrating from Newtonsoft.Json.Schema) to the JSON generated schema through JsonSchemaExporterOptions.TransformSchemaNode. However, the built-in generator transforms part of the schema into a $ref before I can apply my own transformations, resulting in an incorrect schema because the values of the attributes are not the same. Here's an example:

[TypeArgumentRegularExpression("[A-Za-z]+", 0)]
[TypeArgumentRegularExpression("[0-9]+", 1)]
public Dictionary<string, string[]>? Dict { get; set; }

[TypeArgumentRegularExpression("[A-Z]+", 0)]
[TypeArgumentRegularExpression("[a-z]+", 1)]
[TypeArgumentRegularExpression("[0-9]+", 2)]
public Dictionary<string, Dictionary<string, string[]>>? Dict2 { get; set; }

Note that TypeArgumentRegularExpression is a custom attribute based on System.ComponentModel.DataAnnotations.RegularExpressionAttribute which allows me to specify to which TKey/TValue the regex pattern should be applied. The resulting schema looks like:

"properties": {
  "Dict": {
    "type": "object",
    "additionalProperties": false,
    "patternProperties": {
      "[A-Za-z]\u002B": {
        "type": "array",
        "items": {
          "type": "string",
          "pattern": "[0-9]\u002B"
        }
      }
    }
  },
  "Dict2": {
    "type": "object",
    "additionalProperties": false,
    "patternProperties": {
      "[A-Z]\u002B": {
        "$ref": "#/properties/Dict"
      }
    }
  }
}

As you can see, the TValue of the second dictionary has been turned into a $ref to the first dictionary, even though it has a different regex pattern for TKey (Dict's TKey is [A-Za-z]+, but Dict2-TValue's TKey only allows [a-z]+).

I think the easiest solution for this would be an option to disable generating $refs.

API Proposal

namespace System.Text.Json.Schema;

public sealed class JsonSchemaExporterOptions
{
    public bool GenerateRefs { get; init; }
}

API Usage

var transformer = new MyJsonSchemaTransformer();

var jsonSchemaExporterOptions = new JsonSchemaExporterOptions
{
    TreatNullObliviousAsNonNullable = true,
    TransformSchemaNode = transformer.TransformSchemaNode,
    GenerateRefs = false,
};

var result = jsonSerializerOptions.GetJsonSchemaAsNode(typeof(MyObject), jsonSchemaExporterOptions).ToString();

Alternative Designs

No response

Risks

No response