From 3848fa687288a92d544a79eefe8fe18330bc59d9 Mon Sep 17 00:00:00 2001
From: Brown <github@muglug.com>
Date: Thu, 23 Jul 2020 01:48:06 -0400
Subject: [PATCH] Fix #3870 - mark properties as reference-free only for
 externally-immutable classes

---
 .../Analyzer/FunctionLikeAnalyzer.php         |  4 +--
 tests/ImmutableAnnotationTest.php             | 26 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/Psalm/Internal/Analyzer/FunctionLikeAnalyzer.php b/src/Psalm/Internal/Analyzer/FunctionLikeAnalyzer.php
index eb00d42c8..5f4c2c347 100644
--- a/src/Psalm/Internal/Analyzer/FunctionLikeAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/FunctionLikeAnalyzer.php
@@ -216,9 +216,7 @@ abstract class FunctionLikeAnalyzer extends SourceAnalyzer
 
                 $context->vars_in_scope['$this'] = new Type\Union([$this_object_type]);
 
-                if ($storage->external_mutation_free
-                    && !$storage->mutation_free_inferred
-                ) {
+                if ($appearing_class_storage->external_mutation_free) {
                     $context->vars_in_scope['$this']->reference_free = true;
 
                     if ($this->function->name->name !== '__construct') {
diff --git a/tests/ImmutableAnnotationTest.php b/tests/ImmutableAnnotationTest.php
index 0efc66b94..aff3eb487 100644
--- a/tests/ImmutableAnnotationTest.php
+++ b/tests/ImmutableAnnotationTest.php
@@ -699,6 +699,32 @@ class ImmutableAnnotationTest extends TestCase
                     }',
                 'error_message' => 'ImpurePropertyAssignment',
             ],
+            'mutationInPropertyAssignment' => [
+                '<?php
+                    class D {
+                        private string $s;
+
+                        public function __construct(string $s) {
+                            $this->s = $s;
+                        }
+
+                        /**
+                         * @psalm-mutation-free
+                         */
+                        public function getShort() : string {
+                            return substr($this->s, 0, 5);
+                        }
+
+                        /**
+                         * @psalm-mutation-free
+                         */
+                        public function getShortMutating() : string {
+                            $this->s .= "hello";
+                            return substr($this->s, 0, 5);
+                        }
+                    }',
+                'error_message' => 'ImpurePropertyAssignment',
+            ],
         ];
     }
 }