[Bug]: Duplicate union types after ClassPropertyProcessor transformation

[ragulka]

What happened?

While using spatie/laravel-typescript-transformer, I noticed that a property typed as /** @var string[]|Collection<int, string> */ can produce string[] | string[] in the generated TypeScript output (only when the fix in PR #136 is present, though).

This becomes apparent when two conditions are met:

1. The FixArrayLikeStructuresClassPropertyProcessor is configured to replace array-like classes (as laravel-typescript-transformer does by registering Collection::class and EloquentCollection::class)
2. The docblock union contains both an explicit array type and an array-like class that resolves to the same array shape after transformation

While the issue manifests when using the Laravel package, the root cause is in the core typescript-transformer package's transformation pipeline, so it should probably be addressed here.

When a property has a PHPDoc union type that includes both an array-like class (e.g. Collection<int, string>) and its equivalent array type (e.g. string[]), the generated TypeScript output contains duplicate union members like string[] | string[].

TypeScriptUnion deduplicates its members in the constructor via the UniqueTypeScriptNodes trait. At construction time, the two members are different node types (TypeScriptGeneric for Collection and TypeScriptArray for string[]), so both are kept.

FixArrayLikeStructuresClassPropertyProcessor then runs and replaces the TypeScriptGeneric(Collection, ...) node with TypeScriptArray([string]) via a Visitor. Now both members are identical, but deduplication has already run and is not triggered again.

A possible fix could be to add a DeduplicateUnionTypesClassPropertyProcessor that runs as the last processor in the chain. It would walk the type tree and re-deduplicate any TypeScriptUnion members after all other processors have finished their transformations.

How to reproduce the bug

Given a class with a property typed as:

/** @var Collection<int, string>|string[] */
public array $items;

When FixArrayLikeStructuresClassPropertyProcessor is configured to replace Collection, the output is:

items: string[] | string[]

Instead of the expected:

items: string[]

Package Version

3.1.1

PHP Version

8.5.4

Which operating systems does with happen with?

macOS

Notes

No response