isset.variable - Phpstan

Code example

php

<?php declare(strict_types = 1);

function doFoo(): void
{
	if (isset($undefined)) { // ERROR: Variable $undefined in isset() is never defined.
		echo $undefined;
	}
}

Why is it reported?

The variable checked inside isset() is never defined in the current scope. The isset() language construct checks whether a variable exists and is not null. When used on a variable that is never defined, the result is always false. This usually indicates a typo in the variable name or a missing assignment.

How to fix it

Define the variable before checking it, or fix the variable name if it is a typo:

diff-php

 <?php declare(strict_types = 1);

 function doFoo(): void
 {
-	if (isset($undefined)) {
-		echo $undefined;
+	$value = getValue();
+	if (isset($value)) {
+		echo $value;
 	}
 }

If the variable comes from a dynamic source (e.g., extracted variables), make the data flow explicit:

diff-php

 <?php declare(strict_types = 1);

-function doFoo(): void
+function doFoo(?string $name = null): void
 {
-	if (isset($undefined)) {
-		echo $undefined;
+	if (isset($name)) {
+		echo $name;
 	}
 }