Prevent false-positive in get_parent_class() on interfaces

src/Type/Php/GetParentClassDynamicFunctionReturnTypeExtension.php

@@ -82,7 +82,15 @@ private function findParentClassNameType(string $className): Type
 			]);
 		}
 
-		return $this->findParentClassType($this->reflectionProvider->getClass($className));
+		$classReflection = $this->reflectionProvider->getClass($className);
+		if ($classReflection->isInterface()) {
+			return new UnionType([
+				new ClassStringType(),
+				new ConstantBooleanType(false),
+			]);
+		}
+
+		return $this->findParentClassType($classReflection);
 	}
 
 	private function findParentClassType(

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1244,6 +1244,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9062.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/object-shape.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/memcache-get.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-4302b.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-4302b.php

@@ -0,0 +1,20 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4302b;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function theMethod(MyInterface $interface, MyClass $class, MySubClass $subclass) {
+		assertType('class-string|false', get_parent_class($interface));
+		assertType('false', get_parent_class($class));
+		assertType("'Bug4302b\\\\MyClass'", get_parent_class($subclass));
+	}
+}
+
+interface MyInterface {}
+
+class MyClass implements MyInterface {}
+
+class MySubClass extends MyClass {}

tests/PHPStan/Rules/Comparison/IfConstantConditionRuleTest.php

@@ -144,4 +144,10 @@ public function testBug8485(): void
 		$this->analyse([__DIR__ . '/data/bug-8485.php'], []);
 	}
 
+	public function testBug4302(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-4302.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-4302.php

@@ -0,0 +1,14 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4302;
+
+class HelloWorld
+{
+	public function theMethod(MyInterface $object) {
+		if (get_parent_class($object)) {
+			return 1;
+		}
+	}
+}
+
+interface MyInterface {}