From 65efab3a8de2a99732c377971c958eebb09e98dc Mon Sep 17 00:00:00 2001
From: orklah <ronan_morin@hotmail.com>
Date: Sun, 9 Jan 2022 15:48:58 +0100
Subject: [PATCH 1/2] keep class-strings through array_merge

---
 .../ArrayMergeReturnTypeProvider.php           |  9 +++++++++
 tests/ArrayFunctionCallTest.php                | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/Psalm/Internal/Provider/ReturnTypeProvider/ArrayMergeReturnTypeProvider.php b/src/Psalm/Internal/Provider/ReturnTypeProvider/ArrayMergeReturnTypeProvider.php
index 578560b635c..63059484798 100644
--- a/src/Psalm/Internal/Provider/ReturnTypeProvider/ArrayMergeReturnTypeProvider.php
+++ b/src/Psalm/Internal/Provider/ReturnTypeProvider/ArrayMergeReturnTypeProvider.php
@@ -50,6 +50,7 @@ public static function getFunctionReturnType(FunctionReturnTypeProviderEvent $ev
         $codebase = $statements_source->getCodebase();
 
         $generic_properties = [];
+        $class_strings = [];
         $all_keyed_arrays = true;
         $all_int_offsets = true;
         $all_nonempty_lists = true;
@@ -107,6 +108,10 @@ public static function getFunctionReturnType(FunctionReturnTypeProviderEvent $ev
                                     continue;
                                 }
 
+                                if (isset($unpacked_type_part->class_strings[$key])) {
+                                    $class_strings[$key] = true;
+                                }
+
                                 if (!isset($generic_properties[$key]) || !$type->possibly_undefined) {
                                     $generic_properties[$key] = $type;
                                 } else {
@@ -218,6 +223,10 @@ public static function getFunctionReturnType(FunctionReturnTypeProviderEvent $ev
         ) {
             $objectlike = new TKeyedArray($generic_properties);
 
+            if ($class_strings !== []) {
+                $objectlike->class_strings = $class_strings;
+            }
+
             if ($all_nonempty_lists || $all_int_offsets) {
                 $objectlike->is_list = true;
             }
diff --git a/tests/ArrayFunctionCallTest.php b/tests/ArrayFunctionCallTest.php
index f504a6f0def..01954168671 100644
--- a/tests/ArrayFunctionCallTest.php
+++ b/tests/ArrayFunctionCallTest.php
@@ -2121,6 +2121,24 @@ function foo(): array
                         return $a;
                     }',
             ],
+            'arrayUnshiftOnEmptyArrayMeansNonEmptyList' => [
+                '<?php
+
+                    class A {
+                        /** @var array<class-string, string> */
+                        private array $a;
+
+                        public function __construct() {
+                            $this->a = [];
+                        }
+
+                        public function handle(): void {
+                            $b = [A::class => "d"];
+                            $this->a = array_merge($this->a, $b);
+                        }
+                    }
+                    ',
+            ],
         ];
     }
 

From 52ae26f143fda0ebab57a00b7703a75496837a76 Mon Sep 17 00:00:00 2001
From: orklah <ronan_morin@hotmail.com>
Date: Sun, 9 Jan 2022 15:53:43 +0100
Subject: [PATCH 2/2] fix test

---
 tests/ArrayFunctionCallTest.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/ArrayFunctionCallTest.php b/tests/ArrayFunctionCallTest.php
index 01954168671..b06a524a54b 100644
--- a/tests/ArrayFunctionCallTest.php
+++ b/tests/ArrayFunctionCallTest.php
@@ -2121,7 +2121,7 @@ function foo(): array
                         return $a;
                     }',
             ],
-            'arrayUnshiftOnEmptyArrayMeansNonEmptyList' => [
+            'keepClassStringInOffsetThroughArrayMerge' => [
                 '<?php
 
                     class A {