Mark class_exists, interface_exists, trait_exists, and enum_exists as having no side effects in function metadata

src/Node/Expr/AlwaysRememberedExpr.php

@@ -7,6 +7,7 @@
 use PHPStan\Node\VirtualNode;
 use PHPStan\Type\Type;
 
+/** Wraps an expression so its type is always remembered in the scope, bypassing impurity checks. */
 final class AlwaysRememberedExpr extends Expr implements VirtualNode
 {
 

src/Type/Php/ClassExistsFunctionTypeSpecifyingExtension.php

@@ -12,7 +12,9 @@
 use PHPStan\Analyser\TypeSpecifierAwareExtension;
 use PHPStan\Analyser\TypeSpecifierContext;
 use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Node\Expr\AlwaysRememberedExpr;
 use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\BooleanType;
 use PHPStan\Type\ClassStringType;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\Constant\ConstantStringType;
@@ -47,10 +49,11 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 		$args = $node->getArgs();
 		$argType = $scope->getType($args[0]->value);
 		if ($argType instanceof ConstantStringType) {
+			$funcCall = new FuncCall(new FullyQualified('class_exists'), [
+				new Arg(new String_(ltrim($argType->getValue(), '\\'))),
+			]);
 			return $this->typeSpecifier->create(
-				new FuncCall(new FullyQualified('class_exists'), [
-					new Arg(new String_(ltrim($argType->getValue(), '\\'))),
-				]),
+				new AlwaysRememberedExpr($funcCall, new BooleanType(), new BooleanType()),
 				new ConstantBooleanType(true),
 				$context,
 				$scope,

tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php

@@ -109,3 +109,50 @@ function test(): void
 		assertType('int', impure());
 	}
 }
+
+function testClassExistsRemembered(): void
+{
+	if (\class_exists('Bug8579RememberedA')) {
+		assertType('true', \class_exists('Bug8579RememberedA'));
+	} else {
+		assertType('bool', \class_exists('Bug8579RememberedA'));
+	}
+
+	assertType('bool', \class_exists('Bug8579RememberedA'));
+}
+
+function testClassExistsFalseNotRemembered(): void
+{
+	if (!\class_exists('Bug8579FalseNotRememberedA')) {
+		assertType('bool', \class_exists('Bug8579FalseNotRememberedA'));
+	}
+
+	assertType('bool', \class_exists('Bug8579FalseNotRememberedA'));
+}
+
+function testInterfaceExistsFalseNotRemembered(): void
+{
+	if (!\interface_exists('Bug8579FalseNotRememberedC')) {
+		assertType('bool', \interface_exists('Bug8579FalseNotRememberedC'));
+	}
+
+	assertType('bool', \interface_exists('Bug8579FalseNotRememberedC'));
+}
+
+function testTraitExistsFalseNotRemembered(): void
+{
+	if (!\trait_exists('Bug8579FalseNotRememberedD')) {
+		assertType('bool', \trait_exists('Bug8579FalseNotRememberedD'));
+	}
+
+	assertType('bool', \trait_exists('Bug8579FalseNotRememberedD'));
+}
+
+function testEnumExistsFalseNotRemembered(): void
+{
+	if (!\enum_exists('Bug8579FalseNotRememberedE')) {
+		assertType('bool', \enum_exists('Bug8579FalseNotRememberedE'));
+	}
+
+	assertType('bool', \enum_exists('Bug8579FalseNotRememberedE'));
+}

tests/PHPStan/Rules/Classes/InstantiationDoNotRememberPossiblyImpureValuesRuleTest.php

@@ -0,0 +1,35 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Classes;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use function array_merge;
+
+/**
+ * @extends RuleTestCase<InstantiationRule>
+ */
+class InstantiationDoNotRememberPossiblyImpureValuesRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return self::getContainer()->getByType(InstantiationRule::class);
+	}
+
+	public function testBug8579(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-8579.php'], []);
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return array_merge(
+			parent::getAdditionalConfigFiles(),
+			[
+				__DIR__ . '/doNotRememberPossiblyImpureValues.neon',
+			],
+		);
+	}
+
+}

tests/PHPStan/Rules/Classes/data/bug-8579.php

@@ -0,0 +1,13 @@
+<?php
+
+if (!class_exists('NonexistentClassBug8579')) throw new \Exception('nonexistentclass');
+$x = new \NonexistentClassBug8579();
+
+if (!interface_exists('NonexistentInterfaceBug8579')) throw new \Exception('nonexistentinterface');
+$x = new \NonexistentInterfaceBug8579();
+
+if (!trait_exists('NonexistentTraitBug8579')) throw new \Exception('nonexistenttrait');
+$x = new \NonexistentTraitBug8579();
+
+if (!enum_exists('NonexistentEnumBug8579')) throw new \Exception('nonexistentenum');
+$x = new \NonexistentEnumBug8579();

tests/PHPStan/Rules/Classes/doNotRememberPossiblyImpureValues.neon

@@ -0,0 +1,2 @@
+parameters:
+	rememberPossiblyImpureFunctionValues: false