Mark `class_exists`, `interface_exists`, `trait_exists`, and `enum_exists` as having no side effects in function metadata by phpstan-bot · Pull Request #5607 · phpstan/phpstan-src

phpstan-bot · 2026-05-06T19:43:35Z

Summary

When rememberPossiblyImpureFunctionValues is set to false, PHPStan incorrectly reports "Instantiated class X not found" even when the instantiation is guarded by class_exists(). The same issue affects interface_exists, trait_exists, and enum_exists.

Changes

Added class_exists, interface_exists, trait_exists, and enum_exists to resources/functionMetadata.php with 'hasSideEffects' => false
Updated tests/PHPStan/Reflection/BetterReflection/SourceLocator/AutoloadSourceLocatorTest.php to use the return value of class_exists() (avoids the now-correctly-triggered function.resultUnused warning)
Added regression test tests/PHPStan/Analyser/Bug8579Test.php with test data

Root cause

TypeSpecifier::createForExpr() blocks type narrowing for function calls when rememberPossiblyImpureFunctionValues is false and hasSideEffects is not definitively no. Since class_exists and its siblings were missing from resources/functionMetadata.php, they defaulted to hasSideEffects = maybe (set in NativeFunctionReflectionProvider::findFunctionReflection()). This caused the condition at line 2481 of TypeSpecifier.php (!$this->rememberPossiblyImpureFunctionValues && !$hasSideEffects->no()) to evaluate to true, returning empty SpecifiedTypes and preventing the truthy/falsey narrowing from being stored in the scope.

The function_exists function was already correctly marked as hasSideEffects => false in the metadata and was unaffected. The fix brings the other *_exists functions in line with it.

Test

tests/PHPStan/Analyser/Bug8579Test.php — runs full analysis with rememberPossiblyImpureFunctionValues: false config and verifies that class_exists() guards prevent the "class not found" error
Analogous cases (interface_exists, trait_exists, enum_exists) were verified via direct analysis and confirmed working

Fixes phpstan/phpstan#8579

…ists` 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

VincentLanglet

This is semantic wrong because those function depends on other parameters.
One *_exists function could return false and then true later.

But there is something specific to them, as soon as they return true, it stay true. Once a class is loaded in PHP, it cannot be unloaded within the same process.

…pe narrowing Instead of incorrectly marking class_exists, interface_exists, trait_exists, and enum_exists as having no side effects (they trigger autoloading), wrap the FuncCall in AlwaysRememberedExpr in ClassExistsFunctionTypeSpecifyingExtension. This bypasses the rememberPossiblyImpureFunctionValues check in TypeSpecifier::createForExpr() while keeping the correct hasSideEffects semantics. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

phpstan-bot · 2026-05-06T20:54:08Z

Done. Here's a summary of what changed:

Problem: The reviewer correctly pointed out that class_exists, interface_exists, trait_exists, and enum_exists DO have side effects (they trigger autoloading), so marking them as hasSideEffects => false in functionMetadata.php was semantically wrong.

Root cause: When rememberPossiblyImpureFunctionValues is false, TypeSpecifier::createForExpr() blocks type narrowing for any function without hasSideEffects = no. The ClassExistsFunctionTypeSpecifyingExtension calls typeSpecifier->create() with a FuncCall, which hits this impurity check and returns empty SpecifiedTypes.

Fix: Instead of lying about side effects, wrap the FuncCall in AlwaysRememberedExpr in the extension. This is an existing mechanism that bypasses the impurity check in createForExpr() (since AlwaysRememberedExpr is not a FuncCall), and when applied to the scope via MutatingScope::specifyExpressionType(), it propagates the type to the inner FuncCall too. This way isInClassExists() still finds the stored type when checking class existence.

Changes:

Reverted all 4 hasSideEffects => false entries from functionMetadata.php
Modified ClassExistsFunctionTypeSpecifyingExtension to wrap the FuncCall in AlwaysRememberedExpr
Reverted the unnecessary test change in AutoloadSourceLocatorTest.php
Kept the regression test Bug8579Test.php (still passes)

VincentLanglet

Add test to ensure that a false result for class_exists is still not always remembered when we don't remember possibly impure function.

When rememberPossiblyImpureFunctionValues is false, a false result from class_exists() must not be permanently cached — a subsequent class_exists() call for the same class should still be able to return true (since the class could be autoloaded between calls). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

phpstan-bot · 2026-05-06T21:15:13Z

Pushed. Here's what I added to address the review:

New test method testClassExistsFalseNotAlwaysRemembered() in Bug8579Test.php
New test data file bug-8579-false-not-remembered.php with two scenarios:
1. class_exists returns false (falsy if branch not exiting), then a second class_exists for the same class still works and allows instantiation
2. Same pattern but using if/else — the else branch sees class_exists as false, but after the block, a subsequent class_exists check can still return true

Both scenarios run with rememberPossiblyImpureFunctionValues: false and verify no errors are reported, ensuring the false result from class_exists() is not permanently cached. All tests (11996) and make phpstan pass.

staabm · 2026-05-07T05:47:19Z

+
+use PHPStan\Testing\PHPStanTestCase;
+
+class Bug8579Test extends PHPStanTestCase


why do we need such new test? can't we test it with a regular rule-test?

Done. Here's what I changed to address staabm's review:

Converted Bug8579Test to a standard rule test: Created InstantiationDoNotRememberPossiblyImpureValuesRuleTest extending RuleTestCase<InstantiationRule> with rememberPossiblyImpureFunctionValues: false config, following the same pattern as MatchExpressionDoNotRememberPossiblyImpureValuesRuleTest.

Converted the false-not-remembered test to assertType: Added two assertType('bool', class_exists(...)) assertions to the existing do-not-remember-possibly-impure-function-values.php test data file, verifying that a class_exists false result is not permanently remembered after branch merges.

Deleted the old custom test: Removed Bug8579Test.php and its data files (bug-8579.php, bug-8579-false-not-remembered.php) from the Analyser test directory.

All 11997 tests pass and make phpstan reports no errors.

staabm · 2026-05-07T05:47:36Z

+	// The false result must not be permanently remembered,
+	// so a subsequent class_exists check can still return true


can this be tested via assertType() in a nsrt test?

Move the Bug8579 regression test from a custom Analyser test to a standard RuleTestCase for InstantiationRule with rememberPossiblyImpureFunctionValues: false config. Convert the class_exists false-not-remembered test to assertType assertions in the existing DoNotRememberPossiblyImpureFunctionValues test data file. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

VincentLanglet · 2026-05-07T07:05:26Z

+		// class_exists returned false here, but we don't exit
+	}
+
+	assertType('bool', class_exists('Bug8579FalseNotRememberedA'));


Also add assert inside the if

Done. Added assertType('bool', class_exists(...)) assertions inside the if branches as requested by VincentLanglet. The expected type is bool (not true/false) because with rememberPossiblyImpureFunctionValues: false, function call results are not narrowed within branches — only the class existence narrowing (used by instantiation checks) is preserved via AlwaysRememberedExpr. All 12000 tests pass and make phpstan reports no errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

staabm · 2026-05-07T08:36:25Z

 		$args = $node->getArgs();
 		$argType = $scope->getType($args[0]->value);
 		if ($argType instanceof ConstantStringType) {
+			$funcCall = new FuncCall(new FullyQualified('class_exists'), [


per PR title I expect a tests (and fixes) also for interface_exists, trait_exists, and enum_exists

Pushed. Here's what was done to address staabm's review:

1. Added interface_exists/trait_exists/enum_exists tests (tests/PHPStan/Rules/Classes/data/bug-8579.php): Added instantiation guards using all four *_exists functions, not just class_exists. The InstantiationDoNotRememberPossiblyImpureValuesRuleTest now covers all four functions with rememberPossiblyImpureFunctionValues: false.

2. Fixed nsrt assertions to actually test the fix (tests/PHPStan/Analyser/data/do-not-remember-possibly-impure-function-values.php): The previous assertions used unqualified class_exists(...) which produced a different expression key (class_exists(...)) than what the extension stores (\class_exists(...) via FullyQualified), so they always got bool regardless of the fix. Changed to \class_exists(...) (fully qualified) so the key matches. The truthy branch now correctly asserts 'true' — verified this fails before the fix and passes after.

All 12000 tests pass and make phpstan reports no errors.

staabm · 2026-05-07T08:41:04Z

 	}
 }
+
+function testClassExistsFalseNotRemembered(): void


all these nsrt tests did not fail before this PR. is it intentional?

should we have this very same test-lines in a nsrt test with rememberPossiblyImpureFunctionValues: false?

staabm · 2026-05-07T08:45:51Z

-				new FuncCall(new FullyQualified('class_exists'), [
-					new Arg(new String_(ltrim($argType->getValue(), '\\'))),
-				]),
+				new AlwaysRememberedExpr($funcCall, new BooleanType(), new BooleanType()),


I always wondered what the use-case is for AlwaysRememberedExpr and when it is expected to be used. would be great this could be documented in the AlwaysRememberedExpr-class

…rtions - Add interface_exists, trait_exists, and enum_exists guard tests to bug-8579.php rule test data, matching the existing class_exists test - Fix nsrt assertions in do-not-remember test to use fully qualified \class_exists() so the expression key matches the stored type from AlwaysRememberedExpr — the truthy-branch assertType('true') now correctly fails without the fix and passes with it - Replace tests that passed trivially (asserting 'bool' with unqualified class_exists, which never matched the stored key) Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

VincentLanglet reviewed May 6, 2026

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staabm reviewed May 7, 2026

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VincentLanglet reviewed May 7, 2026

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Add assertType inside if branches for class_exists do-not-remember test

3567b00

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

VincentLanglet approved these changes May 7, 2026

View reviewed changes

VincentLanglet requested a review from staabm May 7, 2026 07:22

VincentLanglet self-assigned this May 7, 2026

staabm reviewed May 7, 2026

View reviewed changes


		use PHPStan\Testing\PHPStanTestCase;

		class Bug8579Test extends PHPStanTestCase

		// The false result must not be permanently remembered,
		// so a subsequent class_exists check can still return true

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phpstan-bot commented May 6, 2026

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