Change return types of through (pagination) and transform (collection) (#56105)

Author: glamorous

src/Illuminate/Collections/Collection.php

@@ -1729,8 +1729,10 @@ public function takeWhile($value)
     /**
      * Transform each item in the collection using a callback.
      *
-     * @param  callable(TValue, TKey): TValue  $callback
-     * @return $this
+     * @template TMapValue
+     *
+     * @param  callable(TValue, TKey): TMapValue  $callback
+     * @return $this<TKey, TMapValue>
      */
     public function transform(callable $callback)
     {

src/Illuminate/Pagination/AbstractPaginator.php

@@ -353,8 +353,10 @@ public function lastItem()
     /**
      * Transform each item in the slice of items using a callback.
      *
-     * @param  callable  $callback
-     * @return $this
+     * @template TMapValue
+     *
+     * @param  callable(TValue, TKey): TMapValue  $callback
+     * @return $this<TKey, TMapValue>
      */
     public function through(callable $callback)
     {

types/Support/Collection.php

@@ -1049,13 +1049,20 @@ function ($collection, $count) {
 assertType('Illuminate\Support\Collection<int, User>', $collection->splice(1));
 assertType('Illuminate\Support\Collection<int, User>', $collection->splice(1, 1, [new User]));
 
-assertType('Illuminate\Support\Collection<int, User>', $collection->transform(function ($user, $int) {
+assertType('mixed', $collection->transform(function ($user, $int) {
     assertType('User', $user);
     assertType('int', $int);
 
     return new User;
 }));
 
+assertType('mixed', $collection->transform(function ($user, $int): int {
+    assertType('User', $user);
+    assertType('int', $int);
+
+    return $int * 2;
+}));
+
 assertType('Illuminate\Support\Collection<int, User>', $collection->add(new User));
 
 /**