fix: deduplicate identical sub-schemas with same title

[uprising8664]

Summary

This PR fixes an issue where identical sub-schemas with the same title would generate duplicate TypeScript interface declarations. The fix adds structural hash-based deduplication that tracks emitted type names and reuses them when the same schema structure appears multiple times.

Problem

Previously, when a dereferenced JSON Schema contained the same sub-schema structure multiple times (common in oneOf, anyOf, allOf compositions), the compiler would generate duplicate TypeScript interfaces:

Example

Input Schema:

{
  "title": "Example",
  "type": "object",
  "properties": {
    "user": {
      "oneOf": [
        {
          "title": "Address",
          "type": "object",
          "properties": {
            "street": { "type": "string" },
            "city": { "type": "string" }
          },
          "required": ["street", "city"]
        },
        {
          "title": "Contact",
          "type": "object",
          "properties": {
            "email": { "type": "string" }
          }
        }
      ]
    },
    "billing": {
      "title": "Address",
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "city": { "type": "string" }
      },
      "required": ["street", "city"]
    },
    "shipping": {
      "anyOf": [
        {
          "title": "Address",
          "type": "object",
          "properties": {
            "street": { "type": "string" },
            "city": { "type": "string" }
          },
          "required": ["street", "city"]
        },
        {
          "title": "Contact",
          "type": "object",
          "properties": {
            "phone": { "type": "string" }
          }
        }
      ]
    }
  }
}

Before (duplicate declarations):

export interface Address {
  street: string;
  city: string;
}
export interface Address1 {
  street: string;
  city: string;
}
export interface Address2 {
  street: string;
  city: string;
}

After (single declaration):

export interface Example {
  user?: Address | Contact;
  billing?: Address;
  shipping?: Address | Contact1;
  [k: string]: unknown;
}
export interface Address {
  street: string;
  city: string;
  [k: string]: unknown;
}
export interface Contact {
  email?: string;
  [k: string]: unknown;
}
export interface Contact1 {
  phone?: string;
  [k: string]: unknown;
}

Note: The Address schema appears 3 times in the input but only generates 1 interface in the output.

Enum Deduplication

The same deduplication now applies to enums (both enum declarations via tsEnumNames and union types).

Named Enum (tsEnumNames)

Input Schema:

{
  "title": "Example",
  "type": "object",
  "properties": {
    "primary": {
      "title": "Status",
      "type": "string",
      "enum": ["active", "inactive"],
      "tsEnumNames": ["Active", "Inactive"]
    },
    "secondary": {
      "title": "Status",
      "type": "string",
      "enum": ["active", "inactive"],
      "tsEnumNames": ["Active", "Inactive"]
    }
  }
}

Before (duplicate declarations):

export enum Status {
  Active = "active",
  Inactive = "inactive",
}
export enum Status1 {
  Active = "active",
  Inactive = "inactive",
}

After (single declaration):

export enum Status {
  Active = "active",
  Inactive = "inactive",
}

Unnamed Enum (union type)

Input Schema:

{
  "title": "Example",
  "type": "object",
  "properties": {
    "primary": {
      "title": "Status",
      "type": "string",
      "enum": ["active", "inactive"]
    },
    "secondary": {
      "title": "Status",
      "type": "string",
      "enum": ["active", "inactive"]
    }
  }
}

Before:

export type Status = "active" | "inactive";
export type Status1 = "active" | "inactive";

After:

export type Status = "active" | "inactive";

Changes

• Add structural hashing to identify identical schemas
• Track emitted type names in generator to prevent duplicates
• Schemas with identical title and structure now reuse the same type definition
• Different structures with the same title still get unique numbered names (e.g., Contact, Contact1)
• Extend standaloneName() dedup cache to work without schema.title (property name used as fallback key)
• Add name-based deduplication to declareEnums() matching the existing pattern in declareNamedInterfaces()
• Add test coverage for duplicate sub-schema and enum scenarios

[evert]

This is awesome!