From 545d6c66da6de433ebad70444282326e33b368b9 Mon Sep 17 00:00:00 2001
From: Hug0-Drelon <hugo.drelon@gmail.com>
Date: Fri, 11 Nov 2022 21:27:06 +0100
Subject: [PATCH 1/2] Special case for mixed type in filter return type.

---
 src/HookCallbackRule.php | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/HookCallbackRule.php b/src/HookCallbackRule.php
index 39bf49e..9bdfdd2 100644
--- a/src/HookCallbackRule.php
+++ b/src/HookCallbackRule.php
@@ -19,6 +19,7 @@
 use PHPStan\Type\Constant\ConstantIntegerType;
 use PHPStan\Type\VerbosityLevel;
 use PHPStan\Type\VoidType;
+use PHPStan\Type\MixedType;
 
 /**
  * @implements \PHPStan\Rules\Rule<\PhpParser\Node\Expr\FuncCall>
@@ -206,8 +207,9 @@ protected function validateFilterReturnType(ParametersAcceptor $callbackAcceptor
     {
         $returnType = $callbackAcceptor->getReturnType();
         $isVoidSuperType = $returnType->isSuperTypeOf(new VoidType());
+        $isMixedType = $returnType->equals(new MixedType());
 
-        if (! $isVoidSuperType->yes()) {
+        if ($isMixedType || $isVoidSuperType->no()) {
             return;
         }
 

From 22fa69d51e903153b8f6cb11ac4ee8d93e4444fe Mon Sep 17 00:00:00 2001
From: Hug0-Drelon <hugo.drelon@gmail.com>
Date: Fri, 11 Nov 2022 21:27:30 +0100
Subject: [PATCH 2/2] Add test for mixed type return type in callback.

---
 tests/data/hook-callback.php | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tests/data/hook-callback.php b/tests/data/hook-callback.php
index bf57d22..0b3fe66 100644
--- a/tests/data/hook-callback.php
+++ b/tests/data/hook-callback.php
@@ -185,6 +185,7 @@
 add_filter('filter', function($one = null, $two = null, $three = null) {
     return 123;
 });
+add_filter('filter', 'return_mixed');
 
 // Action callbacks must return void
 add_action('action', function() {
@@ -248,6 +249,10 @@ function filter_variadic_typed( $one, ...$two ) : int {
     return 123;
 }
 
+function return_mixed($value) : mixed {
+    return $value;
+}
+
 class TestInvokableTyped {
     public function __invoke($one, $two) : int {
         return 123;