Add requiredTypename example demonstrating custom plugin for type-safe __typename handling

[Copilot]

Adds an example demonstrating a custom plugin that adds a requiredTypename() method to interface and union refs, enforcing __typename: string as a required property through TypeScript's type system.

Implementation

Plugin (examples/required-typename/src/required-typename-plugin.ts):

• Extends InterfaceRef, ImplementableInterfaceRef, and UnionRef prototypes with requiredTypename() method
• Returns same ref with updated types requiring __typename: string
• No plugin class or registration—purely additive types and methods

Example Schema:

• Union type (Pet) and interface type (Node) using requiredTypename()
• Omits resolveType/isTypeOf since GraphQL resolves via __typename field directly
• Method chained immediately at definition

// Plugin adds method to refs
const PetUnion = builder.unionType('Pet', {
  types: [DogType, CatType],
}).requiredTypename();

// TypeScript now requires __typename in resolvers
builder.queryType({
  fields: (t) => ({
    pets: t.field({
      type: [PetUnion],
      resolve: () => [
        { __typename: 'Dog', name: 'Fido', breed: 'Golden Retriever' },
        { __typename: 'Cat', name: 'Whiskers', livesRemaining: 9 },
      ],
    }),
  }),
});

Testing: Includes schema tests validating union/interface resolution with __typename.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Demo: requiredTypename</issue_title> <issue_description>Create an example in the examples directory that adds a custom plugin that adds a requiredTypename() method on interface and union refs.

The idea is to just return the same ref, but update the types so that __typename: string is a required property for any fields returning that union or interface The example should have the full plugin with types and the method implementation attached to class proptotypes on a single plugin file and an example schema that can be used to ensure it type checks and works with a simple test.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes hayes/pothos#1556

---

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Latest commit: 4fb633733946010b160481c51697acc654c78ba6

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Project	Deployment	Preview	Comments	Updated (UTC)
pothos	Ready	Preview	Comment	Nov 25, 2025 10:10pm