From 0840e69332b6a0fd5ab35223501b3796a3f08597 Mon Sep 17 00:00:00 2001
From: Oleg Zhulnev <plbsid@gmail.com>
Date: Mon, 3 May 2021 22:40:21 +0300
Subject: [PATCH] Multiplication mutator should not mutate when return value is
 integer

---
 src/Mutator/Arithmetic/Multiplication.php     | 23 +++++++++-
 .../Mutator/Arithmetic/MultiplicationTest.php | 42 +++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/src/Mutator/Arithmetic/Multiplication.php b/src/Mutator/Arithmetic/Multiplication.php
index b3f65eec8..d787964ee 100644
--- a/src/Mutator/Arithmetic/Multiplication.php
+++ b/src/Mutator/Arithmetic/Multiplication.php
@@ -39,6 +39,9 @@
 use Infection\Mutator\GetMutatorName;
 use Infection\Mutator\Mutator;
 use Infection\Mutator\MutatorCategory;
+use Infection\PhpParser\Visitor\ParentConnector;
+use Infection\PhpParser\Visitor\ReflectionVisitor;
+use function is_string;
 use PhpParser\Node;
 
 /**
@@ -94,7 +97,25 @@ public function canMutate(Node $node): bool
             return false;
         }
 
-        return true;
+        $functionScope = $node->getAttribute(ReflectionVisitor::FUNCTION_SCOPE_KEY);
+
+        if (!$functionScope instanceof Node\Stmt\ClassMethod) {
+            return true;
+        }
+
+        $parentNode = ParentConnector::getParent($node);
+
+        if (!$parentNode instanceof Node\Stmt\Return_) {
+            return true;
+        }
+
+        $returnType = $functionScope->getReturnType();
+
+        if ($returnType instanceof Node\Identifier) {
+            $returnType = $returnType->name;
+        }
+
+        return !(is_string($returnType) && $returnType === 'int');
     }
 
     private function isNumericOne(Node $node): bool
diff --git a/tests/phpunit/Mutator/Arithmetic/MultiplicationTest.php b/tests/phpunit/Mutator/Arithmetic/MultiplicationTest.php
index 4aa62f2dc..04b65db6a 100644
--- a/tests/phpunit/Mutator/Arithmetic/MultiplicationTest.php
+++ b/tests/phpunit/Mutator/Arithmetic/MultiplicationTest.php
@@ -135,6 +135,48 @@ public function mutationsProvider(): iterable
 <?php
 
 $a = $b * -1.0;
+PHP
+        ];
+
+        yield 'It does not mutate when class method returns type is integer' => [
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b): int
+    {
+        return $a * $b;
+    }
+};
+PHP
+        ];
+
+        yield 'It mutates when class method returns type is integer' => [
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b): int
+    {
+        $c = $a * $b;
+
+        return 1;
+    }
+};
+PHP,
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b) : int
+    {
+        $c = $a / $b;
+        return 1;
+    }
+};
 PHP
         ];
     }