From ddc8c50d2aad5965749841c395e09e82786a6623 Mon Sep 17 00:00:00 2001
From: Brown <github@muglug.com>
Date: Tue, 31 Mar 2020 11:28:36 -0400
Subject: [PATCH] Prevent some inheritance issues

---
 .../Internal/Type/AssertionReconciler.php     | 25 ++++++++++++++
 .../RedundantConditionTest.php                | 33 +++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/src/Psalm/Internal/Type/AssertionReconciler.php b/src/Psalm/Internal/Type/AssertionReconciler.php
index 3b341c2a2..4387bd020 100644
--- a/src/Psalm/Internal/Type/AssertionReconciler.php
+++ b/src/Psalm/Internal/Type/AssertionReconciler.php
@@ -783,6 +783,31 @@ class AssertionReconciler extends \Psalm\Type\Reconciler
 
             $any_scalar_type_match_found = false;
 
+            if ($code_location
+                && $key
+                && !$is_equality
+                && $new_type_part instanceof TNamedObject
+                && !$new_type_has_interface
+                && (!($statements_analyzer->getSource()->getSource() instanceof TraitAnalyzer)
+                    || ($key !== '$this'
+                        && !($existing_var_type->hasLiteralClassString() && $new_type->hasLiteralClassString())))
+                && TypeAnalyzer::isContainedBy(
+                    $codebase,
+                    $existing_var_type,
+                    $new_type
+                )
+            ) {
+                self::triggerIssueForImpossible(
+                    $existing_var_type,
+                    $old_var_type_string,
+                    $key,
+                    $assertion,
+                    true,
+                    $code_location,
+                    $suppressed_issues
+                );
+            }
+
             $new_type = self::filterTypeWithAnother(
                 $codebase,
                 $existing_var_type,
diff --git a/tests/TypeReconciliation/RedundantConditionTest.php b/tests/TypeReconciliation/RedundantConditionTest.php
index cf1dafdad..b1bf00916 100644
--- a/tests/TypeReconciliation/RedundantConditionTest.php
+++ b/tests/TypeReconciliation/RedundantConditionTest.php
@@ -1307,6 +1307,39 @@ class RedundantConditionTest extends \Psalm\Tests\TestCase
                     if (!is_int(returnsInt())) {}',
                 'error_message' => 'TypeDoesNotContainType',
             ],
+            'classAlwaysParent' => [
+                '<?php
+                    class AParent {}
+
+                    class A extends AParent {
+                        public static function load() : A {
+                            return new A();
+                        }
+                    }
+
+                    $a = A::load();
+
+                    if ($a instanceof AParent) {}',
+                'error_message' => 'RedundantCondition',
+            ],
+            'staticClassIsAlwaysNull' => [
+                '<?php
+                    class A {
+                        /**
+                         * @return ?static
+                         */
+                        public static function load() {
+                            return rand(0, 1)
+                                ? null
+                                : new static();
+                        }
+                    }
+
+                    $a = A::load();
+
+                    if ($a && $a instanceof A) {}',
+                'error_message' => 'RedundantConditionGivenDocblockType',
+            ],
         ];
     }
 }