serialize is not pure for array of object

src/Psalm/Internal/Codebase/Functions.php

@@ -530,12 +530,8 @@ public function isCallMapFunctionPure(
         if ($function_id === 'serialize' && isset($args[0]) && $type_provider) {
             $serialize_type = $type_provider->getType($args[0]->value);
 
-            if ($serialize_type) {
-                foreach ($serialize_type->getAtomicTypes() as $atomic_serialize_type) {
-                    if ($atomic_serialize_type->isObjectType()) {
-                        return false;
-                    }
-                }
+            if ($serialize_type && $serialize_type->canContainObjectType($codebase)) {
+                return false;
             }
         }
 

src/Psalm/Internal/TypeVisitor/CanContainObjectTypeVisitor.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Psalm\Internal\TypeVisitor;
+
+use Psalm\Codebase;
+use Psalm\Internal\Type\Comparator\AtomicTypeComparator;
+use Psalm\Internal\Type\Comparator\UnionTypeComparator;
+use Psalm\Type\Atomic;
+use Psalm\Type\Atomic\TObject;
+use Psalm\Type\NodeVisitor;
+use Psalm\Type\TypeNode;
+use Psalm\Type\Union;
+
+class CanContainObjectTypeVisitor extends NodeVisitor
+{
+    /**
+     * @var bool
+     */
+    private $contains_object_type = false;
+
+    /**
+     * @var Codebase
+     */
+    private $codebase;
+
+    public function __construct(Codebase $codebase)
+    {
+        $this->codebase = $codebase;
+    }
+
+    protected function enterNode(TypeNode $type): ?int
+    {
+        if ($type instanceof Union
+            && (
+                UnionTypeComparator::canBeContainedBy($this->codebase, new Union([new TObject()]), $type)
+                && UnionTypeComparator::canBeContainedBy($this->codebase, $type, new Union([new TObject()]))
+            )
+            ||
+            $type instanceof Atomic
+            && (
+                AtomicTypeComparator::isContainedBy($this->codebase, new TObject(), $type)
+                || AtomicTypeComparator::isContainedBy($this->codebase, $type, new TObject())
+            )
+        ) {
+            $this->contains_object_type = true;
+            return NodeVisitor::STOP_TRAVERSAL;
+        }
+
+        return null;
+    }
+
+    public function matches(): bool
+    {
+        return $this->contains_object_type;
+    }
+}

src/Psalm/Type/Union.php

@@ -7,6 +7,7 @@
 use Psalm\Codebase;
 use Psalm\Internal\DataFlow\DataFlowNode;
 use Psalm\Internal\Type\TypeCombiner;
+use Psalm\Internal\TypeVisitor\CanContainObjectTypeVisitor;
 use Psalm\Internal\TypeVisitor\ContainsClassLikeVisitor;
 use Psalm\Internal\TypeVisitor\ContainsLiteralVisitor;
 use Psalm\Internal\TypeVisitor\FromDocblockSetter;
@@ -1492,6 +1493,15 @@ public function containsAnyLiteral(): bool
         return $literal_visitor->matches();
     }
 
+    public function canContainObjectType(Codebase $codebase): bool
+    {
+        $object_type_visitor = new CanContainObjectTypeVisitor($codebase);
+
+        $object_type_visitor->traverseArray($this->types);
+
+        return $object_type_visitor->matches();
+    }
+
     /**
      * @return list<TTemplateParam>
      */

tests/UnusedCodeTest.php

@@ -751,9 +751,14 @@ public function __wakeup(): void
                         }
                     }
 
-                    function test(): bool {
+                    function test(Foo|int $foo, mixed $bar, iterable $baz): bool {
                         try {
                             serialize(new Foo());
+                            serialize([new Foo()]);
+                            serialize([[new Foo()]]);
+                            serialize($foo);
+                            serialize($bar);
+                            serialize($baz);
                             unserialize("");
                         } catch (\Throwable) {
                             return false;