Fix unknown properties for class extending DateInterval|DatePeriod an…

…d loaded with runtime reflection

src/Reflection/ReflectionProvider/ClassBlacklistReflectionProvider.php

@@ -54,7 +54,17 @@ public function hasClass(string $className): bool
 			}
 		}
 
-		return $this->reflectionProvider->hasClass($className);
+		$has = $this->reflectionProvider->hasClass($className);
+		if (!$has) {
+			return false;
+		}
+
+		$classReflection = $this->reflectionProvider->getClass($className);
+		if ($classReflection->isSubclassOf(\DateInterval::class) || $classReflection->isSubclassOf(\DatePeriod::class)) {
+			return false;
+		}
+
+		return true;
 	}
 
 	public function getClass(string $className): ClassReflection

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -244,6 +244,12 @@ public function testBug3415Two(): void
 		$this->assertCount(0, $errors);
 	}
 
+	public function testBug3468(): void
+	{
+		$errors = $this->runAnalyse(__DIR__ . '/data/bug-3468.php');
+		$this->assertCount(0, $errors);
+	}
+
 	/**
 	 * @param string $file
 	 * @return \PHPStan\Analyser\Error[]

tests/PHPStan/Analyser/data/bug-3468.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace Bug3468;
+
+class NewInterval extends \DateInterval
+{
+}
+
+function (NewInterval $ni): void {
+	$ni->f = 0.1;
+};