Mark private properties unused when referenced only in constructor (#1962)

* Mark private properties unused when referenced only in constructor

If a private property is used only in constructor then most likely
it's a dead code since there is no need to have the class property.
But such static properties can be accessed between the calls.

* Ignore the private property issue on alter

* Fix the related dead code psalm

* Add a missing condition into the test

src/Psalm/Codebase.php

@@ -315,7 +315,6 @@ class Codebase
         );
 
         $this->methods = new Internal\Codebase\Methods(
-            $config,
             $providers->classlike_storage_provider,
             $providers->file_reference_provider,
             $this->classlikes

src/Psalm/Internal/Analyzer/ClassAnalyzer.php

@@ -1232,7 +1232,7 @@ class ClassAnalyzer extends ClassLikeAnalyzer
                     if (IssueBuffer::accepts(
                         new PropertyNotSetInConstructor(
                             'Property ' . $property_id . ' is not defined in constructor of ' .
-                                $this->fq_class_name . ' or in any methods called in the constructor',
+                                $this->fq_class_name . ' and in any methods called in the constructor',
                             $error_location,
                             $property_id
                         ),

src/Psalm/Internal/Codebase/ClassLikes.php

@@ -3,6 +3,7 @@ namespace Psalm\Internal\Codebase;
 
 use function array_merge;
 use function array_pop;
+use function count;
 use function end;
 use function explode;
 use function get_declared_classes;
@@ -1688,11 +1689,26 @@ class ClassLikes
         $codebase = $project_analyzer->getCodebase();
 
         foreach ($classlike_storage->properties as $property_name => $property_storage) {
+            $referenced_property_name = strtolower($classlike_storage->name) . '::$' . $property_name;
             $property_referenced = $this->file_reference_provider->isClassPropertyReferenced(
-                strtolower($classlike_storage->name) . '::$' . $property_name
+                $referenced_property_name
             );
 
-            if (!$property_referenced
+            $property_constructor_referenced = false;
+            if ($property_referenced && $property_storage->visibility === ClassLikeAnalyzer::VISIBILITY_PRIVATE) {
+                $all_method_references = $this->file_reference_provider->getAllMethodReferencesToClassMembers();
+
+                if (isset($all_method_references[$referenced_property_name])
+                    && count($all_method_references[$referenced_property_name]) === 1) {
+                    $constructor_name = strtolower($classlike_storage->name) . '::__construct';
+                    $property_references = $all_method_references[$referenced_property_name];
+
+                    $property_constructor_referenced = isset($property_references[$constructor_name])
+                        && !$property_storage->is_static;
+                }
+            }
+
+            if ((!$property_referenced || $property_constructor_referenced)
                 && (substr($property_name, 0, 2) !== '__' || $property_name === '__construct')
                 && $property_storage->location
             ) {
@@ -1765,7 +1781,8 @@ class ClassLikes
                     );
 
                     if ($codebase->alter_code) {
-                        if ($property_storage->stmt_location
+                        if (!$property_constructor_referenced
+                            && $property_storage->stmt_location
                             && isset($project_analyzer->getIssuesToFix()['UnusedProperty'])
                             && !$has_variable_calls
                             && !IssueBuffer::isSuppressed($issue, $classlike_storage->suppressed_issues)

src/Psalm/Internal/Codebase/Methods.php

@@ -36,11 +36,6 @@ class Methods
      */
     private $classlike_storage_provider;
 
-    /**
-     * @var \Psalm\Config
-     */
-    private $config;
-
     /**
      * @var bool
      */
@@ -72,13 +67,11 @@ class Methods
      * @param ClassLikeStorageProvider $storage_provider
      */
     public function __construct(
-        \Psalm\Config $config,
         ClassLikeStorageProvider $storage_provider,
         FileReferenceProvider $file_reference_provider,
         ClassLikes $classlikes
     ) {
         $this->classlike_storage_provider = $storage_provider;
-        $this->config = $config;
         $this->file_reference_provider = $file_reference_provider;
         $this->classlikes = $classlikes;
         $this->return_type_provider = new MethodReturnTypeProvider();

tests/UnusedCodeTest.php

@@ -580,6 +580,32 @@ class UnusedCodeTest extends TestCase
                     new B();',
                 'error_message' => 'PossiblyUnusedProperty',
             ],
+            'propertyUsedOnlyInConstructor' => [
+                '<?php
+                    class A {
+                        /** @var int */
+                        private $used;
+
+                        /** @var int */
+                        private $unused;
+
+                        /** @var int */
+                        private static $staticUnused;
+
+                        public function __construct() {
+                            $this->used = 4;
+                            $this->unused = 4;
+                            self::$staticUnused = 4;
+                        }
+
+                        public function handle(): void
+                        {
+                            $this->used++;
+                        }
+                    }
+                    (new A())->handle();',
+                'error_message' => 'UnusedProperty',
+            ],
         ];
     }
 }