Add regression test for #11507

tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php

@@ -534,6 +534,14 @@ public function testBug8031(): void
 		$this->analyse([__DIR__ . '/data/bug-8031.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0.0')]
+	public function testBug11507(): void
+	{
+		$this->checkNullables = true;
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-11507.php'], []);
+	}
+
 	public function testBug15245(): void
 	{
 		$this->checkNullables = true;

tests/PHPStan/Rules/Functions/data/bug-11507.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+use function PHPStan\dumpType;
+
+/**
+ * @template TValue
+ */
+class Collection
+{
+	/**
+	* @param array<int, TValue> $items
+	*/ 
+	public function __construct(
+		public array $items,
+	) {}
+
+	 /**
+     * Run a map over each of the items.
+     *
+     * @template TMapValue
+     *
+     * @param  callable(TValue, int=): TMapValue  $callback
+     * @return Collection<TMapValue>
+     */
+	public function map(callable $callback) 
+	{
+		$keys = array_keys($this->items);
+
+		$items = array_map($callback, $this->items);
+
+        $result = array_combine($keys, $items);
+
+		return new self($result);
+	}
+}
+
+/**
+ * @param  Collection<non-empty-array<string>>  $collection
+ * @return Collection<non-empty-array<string>>
+ */
+function foo(Collection $collection)
+{
+	return $collection->map(function (array $item) {
+		$item['foo'] = '100';
+
+		return $item;
+	});
+}