Stop boxing types that recurse only through an array or dictionary

[eyupcanakman]

Motivation

The generator boxes a type whose only self-reference is reached through an array or dictionary. Swift arrays and dictionaries keep their elements in heap-allocated storage, so a reference reached only through them cannot form a value-type cycle and the type does not need a CopyOnWriteBox. Supporting-recursive-types.md already notes that arrays and dictionaries can be considered boxed, so the containing type does not require boxing. Fixes #682.

Modifications

• In ExistingTypeDescription.referencedSchemaComponentName, return nil for .array and .dictionaryValue instead of recursing into them. .optional and .any still recurse.

Result

A type that recurses only through an array or dictionary is generated as a plain struct with stored properties, not a boxed type.

Test Plan

Added two snippet reference tests covering recursion through an array and through a dictionary.

[simonjbeaumont]

This looks good and is a really nice catch. Thanks!

Could we extend the tests to include the mixed case where the schema recurses through a direct ref AND a container.

  Node:
    type: object
    properties:
      parent: { $ref: '#/components/schemas/Node' }        # direct -> must still box
      children:
        type: array
        items: { $ref: '#/components/schemas/Node' }        # container -> must not prevent the box

This presumably should still box.

[eyupcanakman]

Added two mixed-case tests, a Node with a direct parent ref alongside a children array, and the same with a children dictionary. Both still box, since the direct ref forms the value cycle and only the container path stopped contributing one.

[simonjbeaumont]

Thanks for the contribution!