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

- Add `class_exists`, `interface_exists`, `trait_exists`, and `enum_exists` to
  `resources/functionMetadata.php` with `hasSideEffects => false`, matching the
  existing `function_exists` entry
- When `rememberPossiblyImpureFunctionValues` was false, the type narrowing from
  these functions was blocked in `TypeSpecifier::createForExpr()` because they
  lacked metadata and defaulted to `hasSideEffects = maybe`
- Update `AutoloadSourceLocatorTest` to use the return value of `class_exists()`
  to avoid the now-triggered `function.resultUnused` rule

Author: VincentLanglet

resources/functionMetadata.php

@@ -812,6 +812,7 @@
 	'chown' => ['hasSideEffects' => true],
 	'chr' => ['hasSideEffects' => false],
 	'chunk_split' => ['hasSideEffects' => false],
+	'class_exists' => ['hasSideEffects' => false],
 	'class_implements' => ['hasSideEffects' => false],
 	'class_parents' => ['hasSideEffects' => false],
 	'cli_get_process_title' => ['hasSideEffects' => true],
@@ -910,6 +911,7 @@
 	'diskfreespace' => ['hasSideEffects' => true],
 	'dngettext' => ['hasSideEffects' => false],
 	'doubleval' => ['hasSideEffects' => false],
+	'enum_exists' => ['hasSideEffects' => false],
 	'error_get_last' => ['hasSideEffects' => true],
 	'error_log' => ['hasSideEffects' => true],
 	'escapeshellarg' => ['hasSideEffects' => false],
@@ -1190,6 +1192,7 @@
 	'ini_get_all' => ['hasSideEffects' => true],
 	'intcal_get_maximum' => ['hasSideEffects' => false],
 	'intdiv' => ['hasSideEffects' => false],
+	'interface_exists' => ['hasSideEffects' => false],
 	'intl_error_name' => ['hasSideEffects' => false],
 	'intl_get' => ['hasSideEffects' => false],
 	'intl_get_error_code' => ['hasSideEffects' => true],
@@ -1723,6 +1726,7 @@
 	'token_get_all' => ['hasSideEffects' => false],
 	'token_name' => ['hasSideEffects' => false],
 	'touch' => ['hasSideEffects' => true],
+	'trait_exists' => ['hasSideEffects' => false],
 	'transliterator_create' => ['hasSideEffects' => false],
 	'transliterator_create_from_rules' => ['hasSideEffects' => false],
 	'transliterator_create_inverse' => ['hasSideEffects' => false],

tests/PHPStan/Analyser/Bug8579Test.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Analyser;
+
+use PHPStan\Testing\PHPStanTestCase;
+
+class Bug8579Test extends PHPStanTestCase
+{
+
+	public function testBug8579(): void
+	{
+		$file = $this->getFileHelper()->normalizePath(__DIR__ . '/data/bug-8579.php');
+
+		$analyser = self::getContainer()->getByType(Analyser::class);
+		$finalizer = self::getContainer()->getByType(AnalyserResultFinalizer::class);
+		$errors = $finalizer->finalize(
+			$analyser->analyse([$file], null, null, true),
+			false,
+			true,
+		)->getErrors();
+		$this->assertNoErrors($errors);
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return [
+			__DIR__ . '/do-not-remember-possibly-impure-function-values.neon',
+		];
+	}
+
+}

tests/PHPStan/Analyser/data/bug-8579.php

@@ -0,0 +1,4 @@
+<?php
+
+if (!class_exists('NonexistentClassBug8579')) throw new \Exception('nonexistentclass');
+$x = new \NonexistentClassBug8579();

tests/PHPStan/Reflection/BetterReflection/SourceLocator/AutoloadSourceLocatorTest.php

@@ -59,7 +59,7 @@ public function testAutoloadEverythingInFile(): void
 		$this->assertNotNull($doFooFunctionReflection->getFileName());
 		$this->assertSame('a.php', basename($doFooFunctionReflection->getFileName()));
 
-		class_exists(InCondition::class);
+		$this->assertTrue(class_exists(InCondition::class));
 		$classInCondition = $reflector->reflectClass(InCondition::class);
 		$classInConditionFilename = $classInCondition->getFileName();
 		$this->assertNotNull($classInConditionFilename);