Add JSON Schema → C# records source generator

[Copilot]

Introduces a new Roslyn IIncrementalGenerator library that reads .schema.json additional files and emits a #nullable enable C# record hierarchy, with namespacing derived from the file's directory path.

Generator library (src/JsonSchema)

• JsonSchemaGenerator – IIncrementalGenerator; picks up *.schema.json AdditionalFiles, derives namespace from RootNamespace + subdirectory path, derives type name from file name or schema title
• SchemaParser – hand-written recursive descent JSON parser; no external dependencies, safe to run in any Roslyn host; handles type as string or array (["string","null"] → nullable)
• CodeEmitter – emits #nullable enable records with get; init; property accessors; required properties → non-nullable (with = default!; for reference types), optional → nullable; nested object properties → additional sibling records named {Parent}{Prop}; each property is decorated with [JsonPropertyName(...)] and, when available, [Description(...)]

Type mapping

JSON Schema	Format	C#
string	—	string
string	date-time	global::System.DateTimeOffset
string	date / time	DateOnly / TimeOnly
string	uuid/guid	global::System.Guid
integer	— / int64	int / long
number	— / float	double / float
boolean	—	bool
array	—	T[]
object + additionalProperties	—	Dictionary<string, T>
object + properties	—	nested record

Property attributes

Each generated property is decorated with:

• [global::System.Text.Json.Serialization.JsonPropertyName("originalName")] — always present, preserves the original JSON key casing for serialisation round-trips
• [global::System.ComponentModel.Description("...")] — emitted only when the JSON Schema property has a description field

Example

Given Models/Person.schema.json:

{
  "type": "object",
  "required": ["id", "name"],
  "properties": {
    "id":      { "type": "string", "format": "uuid" },
    "name":    { "type": "string", "description": "Full display name" },
    "age":     { "type": "integer" },
    "address": {
      "type": "object",
      "required": ["street"],
      "properties": {
        "street": { "type": "string" },
        "city":   { "type": "string" }
      }
    }
  }
}

Emits:

// <auto-generated/>
#nullable enable

namespace MyApp.Models
{
    public record Person
    {
        [global::System.Text.Json.Serialization.JsonPropertyName("id")]
        public global::System.Guid Id { get; init; }

        [global::System.Text.Json.Serialization.JsonPropertyName("name")]
        [global::System.ComponentModel.Description("Full display name")]
        public string Name { get; init; } = default!;

        [global::System.Text.Json.Serialization.JsonPropertyName("age")]
        public int? Age { get; init; }

        [global::System.Text.Json.Serialization.JsonPropertyName("address")]
        public PersonAddress? Address { get; init; }
    }

    public record PersonAddress
    {
        [global::System.Text.Json.Serialization.JsonPropertyName("street")]
        public string Street { get; init; } = default!;

        [global::System.Text.Json.Serialization.JsonPropertyName("city")]
        public string? City { get; init; }
    }
}

Other changes

• global.json – updated SDK from 6.0.100 (unavailable) to 8.0.100 with latestMinor rollforward
• tests/Tests.JsonSchema – 49 unit tests covering parser, emitter, and the Roslyn generator driver

Original prompt

let's create a new library that uses source generators to create a c# class hierarchy based on the path of a file containing a Json schema.

the generator should support NRE, records, use arrays and dictionaries, and use type annotation to select the correct .net primitive type.

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[Kralizek]

Instead of records with primary constructors, use classic properties with get; init; accessors. Also decorate them with attributes to match the name and the description if available.

[Copilot]

Instead of records with primary constructors, use classic properties with get; init; accessors. Also decorate them with attributes to match the name and the description if available.

Addressed in c9dd4b8 — see the reply above for the full details and a sample of the new generated output.