Fix phpstan/phpstan#13325: RegexIterator returns a generic type with unknown parameters

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);

stubs/iterable.stub

@@ -440,7 +440,7 @@ class RegexIterator extends FilterIterator {
     const USE_KEY = 1 ;
 
     /**
-     * @param Iterator<TKey, TValue> $iterator
+     * @param TIterator $iterator
      * @param self::MATCH|self::GET_MATCH|self::ALL_MATCHES|self::SPLIT|self::REPLACE $mode
      */
     public function __construct(Iterator $iterator, string $regex, int $mode = self::MATCH, int $flags = 0, int $preg_flags = 0) {}

tests/PHPStan/Analyser/nsrt/bug-13325.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Bug13325Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	/**
+	 * @param \Iterator<int, string> $iterator
+	 */
+	public function doFoo(\Iterator $iterator): void
+	{
+		$regexIterator = new \RegexIterator($iterator, '/pattern/');
+		assertType('RegexIterator<int, string, Iterator<int, string>>', $regexIterator);
+	}
+
+	public function doBar(): void
+	{
+		$regexIterator = new \RegexIterator(new \FilesystemIterator('foo'), '/pattern/');
+		assertType('RegexIterator<mixed, mixed, FilesystemIterator>', $regexIterator);
+	}
+
+}

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 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bug13325;
+
+use FilesystemIterator;
+use Iterator;
+use RegexIterator;
+
+final class Foo
+{
+	/** @return RegexIterator<mixed, mixed, Iterator> */
+	public function __invoke(Iterator $iterator): RegexIterator
+	{
+		return new RegexIterator($iterator, 'string');
+	}
+
+	/** @return RegexIterator<mixed, mixed, FilesystemIterator> */
+	public function createRegionIterator(): RegexIterator
+	{
+		return new RegexIterator(
+			new FilesystemIterator('foo'),
+			'/bar/',
+		);
+	}
+}