Added a common return type for Collection::getIterator() method (#1889)

* Adjusted docblock for collections in order to have common type for getIterator() method

* Added a common interface for iterators

src/Propel/Runtime/Collection/Collection.php

@@ -201,7 +201,7 @@ public function setData(array $data): void
     }
 
     /**
-     * @return \Propel\Runtime\Collection\CollectionIterator
+     * @return \Propel\Runtime\Collection\CollectionIterator|\Propel\Runtime\Collection\IteratorInterface
      */
     public function getIterator(): Traversable
     {

src/Propel/Runtime/Collection/CollectionIterator.php

@@ -15,7 +15,7 @@
  *
  * @extends \ArrayIterator<(int|string), mixed>
  */
-class CollectionIterator extends ArrayIterator
+class CollectionIterator extends ArrayIterator implements IteratorInterface
 {
     /**
      * @var \Propel\Runtime\Collection\Collection

src/Propel/Runtime/Collection/IteratorInterface.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * MIT License. This file is part of the Propel package.
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Propel\Runtime\Collection;
+
+use Countable;
+use Iterator;
+
+/**
+ * @extends \Iterator<(int|string), mixed>
+ */
+interface IteratorInterface extends Iterator, Countable
+{
+}

src/Propel/Runtime/Collection/OnDemandCollection.php

@@ -108,10 +108,8 @@ public function fromArray(array $arr): void
         throw new ReadOnlyModelException('The On Demand Collection is read only');
     }
 
-    // IteratorAggregate Interface
-
     /**
-     * @return \Propel\Runtime\Collection\OnDemandIterator
+     * @return \Propel\Runtime\Collection\OnDemandIterator|\Propel\Runtime\Collection\IteratorInterface
      */
     public function getIterator(): Traversable
     {

src/Propel/Runtime/Collection/OnDemandIterator.php

@@ -8,7 +8,6 @@
 
 namespace Propel\Runtime\Collection;
 
-use Iterator;
 use Propel\Runtime\ActiveRecord\ActiveRecordInterface;
 use Propel\Runtime\DataFetcher\DataFetcherInterface;
 use Propel\Runtime\Exception\PropelException;
@@ -19,10 +18,8 @@
  * Class for iterating over a statement and returning one Propel object at a time
  *
  * @author Francois Zaninotto
- *
- * @implements \Iterator<int|string, mixed>
  */
-class OnDemandIterator implements Iterator
+class OnDemandIterator implements IteratorInterface
 {
     /**
      * @var \Propel\Runtime\Formatter\ObjectFormatter