Don't double negate

src/Infection/TrinaryLogicMutator.php

@@ -5,12 +5,13 @@
 use Infection\Mutator\Definition;
 use Infection\Mutator\Mutator;
 use Infection\Mutator\MutatorCategory;
+use Infection\PhpParser\Visitor\ParentConnector;
 use LogicException;
 use PhpParser\Node;
 use function in_array;
 
 /**
- * @implements Mutator<Node\Expr\MethodCall>
+ * @implements Mutator<Node\Expr\MethodCall|Node\Expr\BooleanNot>
  */
 final class TrinaryLogicMutator implements Mutator
 {
@@ -38,6 +39,18 @@ public function getName(): string
 
 	public function canMutate(Node $node): bool
 	{
+		if ($node instanceof Node\Expr\MethodCall) {
+			$parentNode = ParentConnector::getParent($node);
+
+			if ($parentNode instanceof Node\Expr\BooleanNot) {
+				return false;
+			}
+		}
+
+		if ($node instanceof Node\Expr\BooleanNot) {
+			$node = $node->expr;
+		}
+
 		if (!$node instanceof Node\Expr\MethodCall) {
 			return false;
 		}
@@ -55,6 +68,25 @@ public function canMutate(Node $node): bool
 
 	public function mutate(Node $node): iterable
 	{
+		if ($node instanceof Node\Expr\BooleanNot) {
+			$node = $node->expr;
+			if (!$node instanceof Node\Expr\MethodCall) {
+				throw new LogicException();
+			}
+
+			if (!$node->name instanceof Node\Identifier) {
+				throw new LogicException();
+			}
+
+			if ($node->name->name === 'yes') {
+				yield new Node\Expr\MethodCall($node->var, 'no');
+			} else {
+				yield new Node\Expr\MethodCall($node->var, 'yes');
+			}
+
+			return;
+		}
+
 		if (!$node->name instanceof Node\Identifier) {
 			throw new LogicException();
 		}

tests/Infection/TrinaryLogicMutatorTest.php

@@ -78,6 +78,22 @@ public static function mutationsProvider(): iterable
 				$trinary = \PHPStan\Type\IsSuperTypeOfResult::createYes();
 				!$trinary->no();
 				PHP
+,
+		];
+
+		yield 'It does not double negate' => [
+			<<<'PHP'
+				<?php
+				$trinary = \PHPStan\Type\IsSuperTypeOfResult::createYes();
+				!$trinary->yes();
+				PHP
+,
+			<<<'PHP'
+				<?php
+
+				$trinary = \PHPStan\Type\IsSuperTypeOfResult::createYes();
+				$trinary->no();
+				PHP
 ,
 		];
 	}