ArrayItemRemoval should not mutate lists (#1358)

* ArrayItemRemoval should not mutate lists

* Update src/Mutator/Removal/ArrayItemRemoval.php

* Update src/Mutator/Removal/ArrayItemRemoval.php

src/Mutator/Removal/ArrayItemRemoval.php

@@ -41,6 +41,7 @@
 use Infection\Mutator\GetConfigClassName;
 use Infection\Mutator\GetMutatorName;
 use Infection\Mutator\MutatorCategory;
+use Infection\PhpParser\Visitor\ParentConnector;
 use function min;
 use PhpParser\Node;
 use PhpParser\Node\Expr\ArrayItem;
@@ -119,7 +120,22 @@ public function mutate(Node $arrayNode): iterable
 
     public function canMutate(Node $node): bool
     {
-        return $node instanceof Node\Expr\Array_ && count($node->items);
+        if (!$node instanceof Node\Expr\Array_) {
+            return false;
+        }
+
+        if ($node->items === []) {
+            return false;
+        }
+
+        $parent = ParentConnector::findParent($node);
+
+        // Arrays to the left of an assignments are not arrays but lists.
+        if ($parent instanceof Node\Expr\Assign && $parent->var === $node) {
+            return false;
+        }
+
+        return true;
     }
 
     /**

tests/phpunit/Mutator/Removal/ArrayItemRemovalTest.php

@@ -102,5 +102,17 @@ public function mutationsProvider(): iterable
             ],
             ['remove' => 'all', 'limit' => 1],
         ];
+
+        yield 'It does not mutate lists with missing elements' => [
+            '<?php [, $a] = [];',
+        ];
+
+        yield 'It does not mutate lists with one element' => [
+            '<?php [$a] = [];',
+        ];
+
+        yield 'It does not mutate lists with any number of elements' => [
+            '<?php [$a, $b] = [];',
+        ];
     }
 }