Add test

Author: VincentLanglet

tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php

@@ -283,6 +283,13 @@ public function testBug10732(): void
 		$this->analyse([__DIR__ . '/data/bug-10732.php'], []);
 	}
 
+	public function testBug10960(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->checkNullables = true;
+		$this->analyse([__DIR__ . '/data/bug-10960.php'], []);
+	}
+
 	public function testBug11518(): void
 	{
 		$this->checkExplicitMixed = true;

tests/PHPStan/Rules/Functions/data/bug-10960.php

@@ -0,0 +1,26 @@
+<?php declare(strict_types = 1);
+
+namespace Bug10960;
+
+/**
+ * @param array{foo: string} $foo
+ *
+ * @return array{FOO: string}
+ */
+function upperCaseKey(array $foo): array
+{
+	return array_change_key_case($foo, CASE_UPPER);
+}
+
+/**
+ * @param array{FOO: string} $foo
+ *
+ * @return array{foo: string}
+ */
+function lowerCaseKey(array $foo): array
+{
+	return array_change_key_case($foo, CASE_LOWER);
+}
+
+upperCaseKey(['foo' => 'bar']);
+lowerCaseKey(['FOO' => 'bar']);