From 0a54c84055b1dc47852f76f6452ef174d09e5bcd Mon Sep 17 00:00:00 2001
From: kkmuffme <11071985+kkmuffme@users.noreply.github.com>
Date: Fri, 9 Jun 2023 12:37:41 +0200
Subject: [PATCH] readonly does not have write access, therefore is safe as
 long as the type is contained in the parent type

Fix https://github.com/vimeo/psalm/issues/9831#issuecomment-1569022701
---
 src/Psalm/Internal/Analyzer/ClassAnalyzer.php | 15 ++++++++++++++-
 tests/PropertyTypeInvarianceTest.php          | 17 +++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/Psalm/Internal/Analyzer/ClassAnalyzer.php b/src/Psalm/Internal/Analyzer/ClassAnalyzer.php
index fb72507a305..84d33115fd5 100644
--- a/src/Psalm/Internal/Analyzer/ClassAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/ClassAnalyzer.php
@@ -802,7 +802,20 @@ public static function addContextProperties(
                         $codebase,
                     );
 
-                    if ($property_storage->location
+                    if ($guide_property_storage->readonly
+                        && UnionTypeComparator::isContainedBy(
+                            $codebase,
+                            $property_type,
+                            $guide_property_type,
+                            false,
+                            false,
+                            null,
+                            false,
+                            false,
+                        )) {
+                        // if the original property is readonly, it cannot be written
+                        // therefore invariance is not a problem, if the parent type contains the child type
+                    } elseif ($property_storage->location
                         && !$property_type->equals($guide_property_type, false)
                         && $guide_class_storage->user_defined
                     ) {
diff --git a/tests/PropertyTypeInvarianceTest.php b/tests/PropertyTypeInvarianceTest.php
index fdf00095bab..ba4b8a7b11b 100644
--- a/tests/PropertyTypeInvarianceTest.php
+++ b/tests/PropertyTypeInvarianceTest.php
@@ -231,6 +231,23 @@ class Baz extends Bar {
                         public $d;
                     }',
             ],
+            'allowReadonly' => [
+                'code' => '<?php
+                    class ParentClass
+                    {
+                        /**
+                         * @readonly
+                         * @var null|string
+                         */
+                        protected $mightExist;
+                    }
+
+                    class ChildClass extends ParentClass
+                    {
+                        /** @var string */
+                        protected $mightExist = "";
+                    }',
+            ],
         ];
     }