Bleeding edge - report top-level xor because that's probably not what the user intended to do

Author: ondrejmirtes

conf/config.level4.neon

@@ -3,7 +3,6 @@ includes:
 
 rules:
 - PHPStan\Rules\Arrays\DeadForeachRule
-- PHPStan\Rules\DeadCode\NoopRule
 - PHPStan\Rules\DeadCode\UnreachableStatementRule
 - PHPStan\Rules\DeadCode\UnusedPrivateConstantRule
 - PHPStan\Rules\DeadCode\UnusedPrivateMethodRule
@@ -68,6 +67,13 @@ services:
 tags:
 - phpstan.rules.rule
 
+-
+class: PHPStan\Rules\DeadCode\NoopRule
+arguments:
+logicalXor: %featureToggles.logicalXor%
+tags:
+- phpstan.rules.rule
+
 -
 class: PHPStan\Rules\DeadCode\UnusedPrivatePropertyRule
 arguments:

src/Rules/DeadCode/NoopRule.php

@@ -15,7 +15,7 @@
 class NoopRule implements Rule
 {
 
-public function __construct(private ExprPrinter $exprPrinter)
+public function __construct(private ExprPrinter $exprPrinter, private bool $logicalXor)
 {
 }
 
@@ -36,6 +36,15 @@ public function processNode(Node $node, Scope $scope): array
 ) {
 $expr = $expr->expr;
 }
+if ($this->logicalXor && $expr instanceof Node\Expr\BinaryOp\LogicalXor) {
+return [
+RuleErrorBuilder::message(
+'Unused result of "xor" operator.',
+)->line($expr->getLine())
+->tip('This operator has unexpected precedence, try disambiguating the logic with parentheses ().')
+->build(),
+];
+}
 if (
 !$expr instanceof Node\Expr\Variable
 && !$expr instanceof Node\Expr\PropertyFetch

tests/PHPStan/Rules/DeadCode/NoopRuleTest.php

@@ -15,7 +15,7 @@ class NoopRuleTest extends RuleTestCase
 
 protected function getRule(): Rule
 {
-return new NoopRule(new ExprPrinter(new Printer()));
+return new NoopRule(new ExprPrinter(new Printer()), true);
 }
 
 public function testRule(): void
@@ -77,6 +77,11 @@ public function testRule(): void
 'Expression "(string) 1" on a separate line does not do anything.',
 30,
 ],
+[
+'Unused result of "xor" operator.',
+32,
+'This operator has unexpected precedence, try disambiguating the logic with parentheses ().',
+],
 ]);
 }
 

tests/PHPStan/Rules/DeadCode/data/noop.php

@@ -2,7 +2,7 @@
 
 namespace DeadCodeNoop;
 
-function (stdClass $foo) {
+function (stdClass $foo, bool $a, bool $b) {
 $foo->foo();
 
 $arr = [];
@@ -28,4 +28,6 @@ function (stdClass $foo) {
 Foo::TEST;
 
 (string) 1;
+
+$r = $a xor $b;
 };