Do not mutate $var instanceof ClassName inside assert() function …

…as it's impossible or hard to kill

Fixes #1845

src/Mutator/Boolean/InstanceOf_.php

@@ -39,6 +39,7 @@
 use Infection\Mutator\GetMutatorName;
 use Infection\Mutator\Mutator;
 use Infection\Mutator\MutatorCategory;
+use Infection\PhpParser\Visitor\ParentConnector;
 use PhpParser\Node;
 
 /**
@@ -80,6 +81,26 @@ public function mutate(Node $node): iterable
 
     public function canMutate(Node $node): bool
     {
-        return $node instanceof Node\Expr\Instanceof_;
+        if (!$node instanceof Node\Expr\Instanceof_) {
+            return false;
+        }
+
+        if ($this->isArgumentOfAssertFunction($node)) {
+            return false;
+        }
+
+        return true;
+    }
+
+    private function isArgumentOfAssertFunction(Node\Expr\Instanceof_ $node): bool
+    {
+        $parentNode = ParentConnector::findParent($node);
+        $grandParentNode = $parentNode !== null ? ParentConnector::findParent($parentNode) : null;
+
+        if (!$grandParentNode instanceof Node\Expr\FuncCall || !$grandParentNode->name instanceof Node\Name) {
+            return false;
+        }
+
+        return $grandParentNode->name->toLowerString() === 'assert';
     }
 }

tests/phpunit/Mutator/Boolean/InstanceOf_Test.php

@@ -96,5 +96,46 @@ public function mutationsProvider(): iterable
                 ,
             ],
         ];
+
+        yield 'It does not mutate an instanceof comparison inside `assert()` function call with a class literal' => [
+            <<<'PHP'
+<?php
+
+return assert($example instanceof Example);
+PHP
+            ,
+        ];
+
+        yield 'It does not mutate an instanceof comparison inside `assert()` function call with variable' => [
+            <<<'PHP'
+<?php
+
+return assert($example instanceof $foo);
+PHP
+            ,
+        ];
+
+        yield 'It mutates an instanceof comparison inside other than `assert()` functions' => [
+            <<<'PHP'
+<?php
+
+return someFunc($example instanceof $foo);
+PHP
+            ,
+            [
+                <<<'PHP'
+<?php
+
+return someFunc(true);
+PHP
+            ,
+                <<<'PHP'
+<?php
+
+return someFunc(false);
+PHP
+            ,
+            ],
+        ];
     }
 }