Add support for @readonly annotation

src/Psalm/Internal/Analyzer/CommentAnalyzer.php

@@ -96,10 +96,6 @@ class CommentAnalyzer
 
         $comment_text = $comment->getText();
 
-        if (!isset($parsed_docblock['specials']['var']) && !isset($parsed_docblock['specials']['psalm-var'])) {
-            return [];
-        }
-
         $var_line_number = $comment->getLine();
 
         if ($parsed_docblock) {
@@ -184,6 +180,7 @@ class CommentAnalyzer
                 $var_comment->type_end = $type_end;
                 $var_comment->deprecated = isset($parsed_docblock['specials']['deprecated']);
                 $var_comment->internal = isset($parsed_docblock['specials']['internal']);
+                $var_comment->readonly = isset($parsed_docblock['specials']['readonly']);
                 if (isset($parsed_docblock['specials']['psalm-internal'])) {
                     $psalm_internal = reset($parsed_docblock['specials']['psalm-internal']);
                     if ($psalm_internal) {
@@ -202,6 +199,19 @@ class CommentAnalyzer
             }
         }
 
+        if (!$var_comments
+            && (isset($parsed_docblock['specials']['deprecated'])
+                || isset($parsed_docblock['specials']['internal'])
+                || isset($parsed_docblock['specials']['readonly']))
+        ) {
+            $var_comment = new VarDocblockComment();
+            $var_comment->deprecated = isset($parsed_docblock['specials']['deprecated']);
+            $var_comment->internal = isset($parsed_docblock['specials']['internal']);
+            $var_comment->readonly = isset($parsed_docblock['specials']['readonly']);
+
+            $var_comments[] = $var_comment;
+        }
+
         return $var_comments;
     }
 

src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/PropertyAssignmentAnalyzer.php

@@ -14,6 +14,7 @@ use Psalm\CodeLocation;
 use Psalm\Context;
 use Psalm\Issue\DeprecatedProperty;
 use Psalm\Issue\ImplicitToStringCast;
+use Psalm\Issue\InaccessibleProperty;
 use Psalm\Issue\InternalProperty;
 use Psalm\Issue\InvalidPropertyAssignment;
 use Psalm\Issue\InvalidPropertyAssignmentValue;
@@ -614,6 +615,32 @@ class PropertyAssignmentAnalyzer
                             }
                         }
                     }
+
+                    if ($property_storage->readonly) {
+                        $appearing_property_class = $codebase->properties->getAppearingClassForProperty(
+                            $property_id,
+                            true
+                        );
+
+                        if ($appearing_property_class
+                            && !($context->self
+                                && ($appearing_property_class === $context->self
+                                    || $codebase->classExtends($context->self, $appearing_property_class))
+                                && (!$context->calling_method_id
+                                    || \strpos($context->calling_method_id, '::__construct'))
+                            )
+                        ) {
+                            if (IssueBuffer::accepts(
+                                new InaccessibleProperty(
+                                    $property_id . ' is marked readonly',
+                                    new CodeLocation($statements_analyzer->getSource(), $stmt)
+                                ),
+                                $statements_analyzer->getSuppressedIssues()
+                            )) {
+                                // fall through
+                            }
+                        }
+                    }
                 }
 
                 $class_property_type = $codebase->properties->getPropertyType(

src/Psalm/Internal/Scanner/VarDocblockComment.php

@@ -58,4 +58,11 @@ class VarDocblockComment
      * @var null|string
      */
     public $psalm_internal = null;
+
+    /**
+     * Whether or not the property is readonly
+     *
+     * @var bool
+     */
+    public $readonly = false;
 }

src/Psalm/Internal/Visitor/ReflectorVisitor.php

@@ -2967,6 +2967,7 @@ class ReflectorVisitor extends PhpParser\NodeVisitorAbstract implements PhpParse
             $property_storage->deprecated = $var_comment ? $var_comment->deprecated : false;
             $property_storage->internal = $var_comment ? $var_comment->internal : false;
             $property_storage->psalm_internal = $var_comment ? $var_comment->psalm_internal : null;
+            $property_storage->readonly = $var_comment ? $var_comment->readonly : false;
 
             if (!$signature_type && !$doc_var_group_type) {
                 if ($property->default) {

src/Psalm/Storage/PropertyStorage.php

@@ -69,6 +69,11 @@ class PropertyStorage
      */
     public $internal = false;
 
+    /**
+     * @var bool
+     */
+    public $readonly = false;
+
     /**
      * @var null|string
      */

tests/PropertyTypeTest.php

@@ -1661,6 +1661,38 @@ class PropertyTypeTest extends TestCase
                         }
                     }',
             ],
+            'readonlyPropertySetInConstructor' => [
+                '<?php
+                    class A {
+                        /**
+                         * @readonly
+                         */
+                        public string $bar;
+
+                        public function __construct() {
+                            $this->bar = "hello";
+                        }
+                    }
+
+                    echo (new A)->bar;'
+            ],
+            'readonlyPropertySetChildClass' => [
+                '<?php
+                    abstract class A {
+                        /**
+                         * @readonly
+                         */
+                        public string $bar;
+                    }
+
+                    class B extends A {
+                        public function __construct() {
+                            $this->bar = "hello";
+                        }
+                    }
+
+                    echo (new B)->bar;'
+            ],
         ];
     }
 
@@ -2592,6 +2624,61 @@ class PropertyTypeTest extends TestCase
                     }',
                 'error_message' => 'InvalidPropertyAssignmentValue'
             ],
+            'readonlyPropertySetInConstructorAndAlsoAnotherMethodInsideClass' => [
+                '<?php
+                    class A {
+                        /**
+                         * @readonly
+                         */
+                        public string $bar;
+
+                        public function __construct() {
+                            $this->bar = "hello";
+                        }
+
+                        public function setBar() : void {
+                            $this->bar = "goodbye";
+                        }
+                    }',
+                'error_message' => 'InaccessibleProperty',
+            ],
+            'readonlyPropertySetInConstructorAndAlsoAnotherMethodInSublass' => [
+                '<?php
+                    class A {
+                        /**
+                         * @readonly
+                         */
+                        public string $bar;
+
+                        public function __construct() {
+                            $this->bar = "hello";
+                        }
+                    }
+
+                    class B extends A {
+                        public function setBar() : void {
+                            $this->bar = "hello";
+                        }
+                    }',
+                'error_message' => 'InaccessibleProperty',
+            ],
+            'readonlyPropertySetInConstructorAndAlsoOutsideClass' => [
+                '<?php
+                    class A {
+                        /**
+                         * @readonly
+                         */
+                        public string $bar;
+
+                        public function __construct() {
+                            $this->bar = "hello";
+                        }
+                    }
+
+                    $a = new A();
+                    $a->bar = "goodbye";',
+                'error_message' => 'InaccessibleProperty',
+            ],
         ];
     }
 }