Add regression test for 5805

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -918,4 +918,13 @@ public function testBug4173(): void
 		]);
 	}
 
+	public function testBug5805(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = false;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+		$this->analyse([__DIR__ . '/data/bug-5805.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Variables/data/bug-5805.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types = 1);
+
+namespace Bug5805;
+
+(function (): void {
+	if (!($_GET['foo'])) { // if 'foo' is falsy, SET $var
+		$var = "set";
+	}
+
+	if ($_GET['foo']) {
+
+	} else {
+		// Foo is falsy, var should have been set.
+
+		echo $var;
+	}
+})();