fix: Collection::flatMap callback can return Enumerable (#970)

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed template resolution when `flatMap`'s callback returns an `Enumerable`
+
 ## [0.7.13] - 2021-10-14
 
 ### Fixed

stubs/Collection.stub

@@ -84,7 +84,7 @@ class Collection implements \ArrayAccess, Enumerable
 
     /**
      * @template TReturn
-     * @param callable(TValue, TKey): array<TReturn> $callback
+     * @param callable(TValue, TKey): (array<TReturn>|\Illuminate\Support\Enumerable<array-key, TReturn>) $callback
      * @return static<TKey, TReturn>
      */
     public function flatMap(callable $callback) {}

tests/Features/ReturnTypes/CollectionStub.php

@@ -7,6 +7,7 @@
 use App\User;
 use Illuminate\Database\Eloquent\Collection as EloquentCollection;
 use Illuminate\Support\Collection as SupportCollection;
+use function PHPStan\Testing\assertType;
 use Traversable;
 
 class CollectionStub
@@ -156,6 +157,19 @@ public function testFlatMap(EloquentCollection $collection)
         });
     }
 
+    /**
+     * @param  EloquentCollection<User>  $collection
+     */
+    public function testFlatMapWithCollection(EloquentCollection $collection): void
+    {
+        assertType(
+            'Illuminate\Support\Collection<int, App\Account>',
+            $collection->flatMap(function (User $user, int $id) {
+                return $user->accounts;
+            })
+        );
+    }
+
     /**
      * @param  EloquentCollection<User>  $items
      * @return EloquentCollection<User>