Added regression test

Author: staabm

tests/PHPStan/Rules/Comparison/IfConstantConditionRuleTest.php

@@ -173,4 +173,10 @@ public function testBug4912(): void
 		$this->analyse([__DIR__ . '/data/bug-4912.php'], []);
 	}
 
+	public function testBug4864(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-4864.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-4864.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Bug4864;
+
+class Example
+{
+	/** @var mixed */
+	private $value;
+	private bool $isHandled;
+
+	public function fetchValue(callable $f): void
+	{
+		$this->isHandled = false;
+		$this->value = null;
+
+		(function () {
+			$this->isHandled = true;
+			$this->value = 'value';
+		})();
+
+		if ($this->isHandled) {
+			$f($this->value);
+		}
+	}
+}