Solve bug 3979

Author: VincentLanglet

src/Rules/Comparison/ImpossibleCheckTypeFunctionCallRule.php

@@ -7,6 +7,7 @@
 use PHPStan\Parser\LastConditionVisitor;
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
+use function in_array;
 use function sprintf;
 use function strtolower;
 
@@ -37,7 +38,7 @@ public function processNode(Node $node, Scope $scope): array
 		}
 
 		$functionName = (string) $node->name;
-		if (strtolower($functionName) === 'is_a') {
+		if (in_array(strtolower($functionName), ['is_a', 'is_subclass_of'], true)) {
 			return [];
 		}
 		$isAlways = $this->impossibleCheckTypeHelper->findSpecifiedType($scope, $node);

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php

@@ -492,16 +492,7 @@ public function testBug6305(): void
 	{
 		$this->checkAlwaysTrueCheckTypeFunctionCall = true;
 		$this->treatPhpDocTypesAsCertain = true;
-		$this->analyse([__DIR__ . '/data/bug-6305.php'], [
-			[
-				'Call to function is_subclass_of() with Bug6305\B and \'Bug6305\\\A\' will always evaluate to true.',
-				11,
-			],
-			[
-				'Call to function is_subclass_of() with Bug6305\B and \'Bug6305\\\B\' will always evaluate to false.',
-				14,
-			],
-		]);
+		$this->analyse([__DIR__ . '/data/bug-6305.php'], []);
 	}
 
 	public function testBug6698(): void
@@ -1101,4 +1092,11 @@ public function testAlwaysTruePregMatch(): void
 		$this->analyse([__DIR__ . '/data/always-true-preg-match.php'], []);
 	}
 
+	public function testBug3979(): void
+	{
+		$this->checkAlwaysTrueCheckTypeFunctionCall = true;
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-3979.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-3979.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Bug3979;
+
+class A { }
+class B extends A { }
+class C { }
+
+/**
+ * @param mixed $value
+ * @param string $class_type
+ */
+function check_class($value, $class_type): bool
+{
+	if (!is_string($value) || !class_exists($value) ||
+		($class_type && !is_subclass_of($value, $class_type)))
+		return false;
+	return true;
+}
+
+var_dump(check_class("B", "A")); // true
+var_dump(check_class("C", "A")); // false