[FIX] dynamic variable undefined inside isset

src/Rules/Variables/DefinedVariableRule.php

@@ -41,6 +41,11 @@ public function getNodeType(): string
 	public function processNode(Node $node, Scope $scope): array
 	{
 		$errors = [];
+
+		if ($scope->isUndefinedExpressionAllowed($node)) {
+			return [];
+		}
+
 		if (is_string($node->name)) {
 			$variableNameScopes = [$node->name => $scope];
 		} else {
@@ -78,7 +83,7 @@ private function processSingleVariable(Scope $scope, Variable $node, string $var
 			}
 		}
 
-		if ($scope->isInExpressionAssign($node) || $scope->isUndefinedExpressionAllowed($node)) {
+		if ($scope->isInExpressionAssign($node)) {
 			return [];
 		}
 

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -1169,4 +1169,23 @@ public function testBug8719(): void
 		$this->analyse([__DIR__ . '/data/bug-8719.php'], []);
 	}
 
+	public function testBug13353(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = true;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+
+		$this->analyse([__DIR__ . '/data/bug-13353.php'], [
+			[
+				'Variable $bar might not be defined.',
+				11,
+			],
+			[
+				'Undefined variable: $bar',
+				20,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Variables/IssetRuleTest.php

@@ -511,4 +511,11 @@ public function testBug10640(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-10640.php'], []);
 	}
 
+	public function testBug13353(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+
+		$this->analyse([__DIR__ . '/data/bug-13353.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Variables/data/bug-13353.php

@@ -0,0 +1,21 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13353;
+
+$foo = 'bar';
+
+if (!isset($$foo)) {
+	echo 'Wololo';
+}
+
+echo $$foo;
+
+function () {
+	$foo = 'bar';
+
+	if (!isset($$foo)) {
+		echo 'Wololo';
+	}
+
+	echo $$foo;
+};