Fix RegexIterator returning generic type with unresolved template parameters

- Fixed GenericTypeTemplateTraverser to continue traversing into bounds of unresolvable template types
- When a template type (like TIterator) can't be inferred from constructor args, its bound may still contain other template types (TKey, TValue) that need resolution
- Added regression test for phpstan/phpstan#13325

Author: VincentLanglet

src/Analyser/Traverser/GenericTypeTemplateTraverser.php

@@ -26,7 +26,7 @@ public function traverse(Type $type, callable $traverse): Type
 		if ($type instanceof TemplateType && !$type->isArgument()) {
 			$newType = $this->resolvedTemplateTypeMap->getType($type->getName());
 			if ($newType === null || $newType instanceof ErrorType) {
-				return $type->getDefault() ?? $type->getBound();
+				return $traverse($type->getDefault() ?? $type->getBound());
 			}
 
 			return TemplateTypeHelper::generalizeInferredTemplateType($type, $newType);

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -1326,4 +1326,9 @@ public function testBug10924(): void
 		$this->analyse([__DIR__ . '/data/bug-10924.php'], []);
 	}
 
+	public function testBug13325(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-13325.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-13325.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bug13325;
+
+use Iterator;
+use RegexIterator;
+use Traversable;
+
+final class Foo
+{
+	/** @return RegexIterator<mixed, mixed, Traversable<mixed, mixed>> */
+	public function __invoke(Iterator $iterator): RegexIterator
+	{
+		return new RegexIterator($iterator, 'string');
+	}
+}