Error Identifier: logicalXor.rightAlwaysFalse

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Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

function doFoo(bool $flag): bool
{
	$f = false;
	return $flag xor $f;
}

Why is it reported? #

The right side of the xor operator always evaluates to false. This makes the xor expression equivalent to just the left side, because $left xor false always equals $left. The right operand is redundant and likely indicates a logic error.

In the example above, $f is always false, so $flag xor $f is equivalent to $flag.

How to fix it #

Simplify the expression by removing the redundant xor:

 <?php declare(strict_types = 1);
 
 function doFoo(bool $flag): bool
 {
-	$f = false;
-	return $flag xor $f;
+	return $flag;
 }

Or fix the right-side condition so that it can actually evaluate to true:

 <?php declare(strict_types = 1);
 
-function doFoo(bool $flag): bool
+function doFoo(bool $flag, bool $other): bool
 {
-	$f = false;
-	return $flag xor $f;
+	return $flag xor $other;
 }

How to ignore this error #

You can use the identifier logicalXor.rightAlwaysFalse to ignore this error using a comment:

// @phpstan-ignore logicalXor.rightAlwaysFalse
codeThatProducesTheError();

You can also use only the identifier key to ignore all errors of the same type in your configuration file in the ignoreErrors parameter:

parameters:
	ignoreErrors:
		-
			identifier: logicalXor.rightAlwaysFalse

Rules that report this error #

• PHPStan\Rules\Comparison\LogicalXorConstantConditionRule [1]