PCRE problem #4448
Description
Bug report
We got a PHP error after upgrading to PHP 8:
TypeError: preg_replace(): Argument #3 ($subject) must be of type array|string, null given in phpstan-src/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php:207
#0 phpstan-src/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php:207 preg_replace()
#1 phpstan-src/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php:168 PHPStan\Reflection\BetterReflection\SourceLocator\OptimizedDirectorySourceLocator->findSymbols()
#2 phpstan-src/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php:130 PHPStan\Reflection\BetterReflection\SourceLocator\OptimizedDirectorySourceLocator->init()
#3 phpstan-src/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php:57 PHPStan\Reflection\BetterReflection\SourceLocator\OptimizedDirectorySourceLocator->findFileByClass()
#4 phpstan-src/vendor/ondrejmirtes/better-reflection/src/SourceLocator/Type/AggregateSourceLocator.php:35 PHPStan\Reflection\BetterReflection\SourceLocator\OptimizedDirectorySourceLocator->locateIdentifier()
#5 phpstan-src/vendor/ondrejmirtes/better-reflection/src/SourceLocator/Type/MemoizingSourceLocator.php:40 Roave\BetterReflection\SourceLocator\Type\AggregateSourceLocator->locateIdentifier()
#6 phpstan-src/vendor/ondrejmirtes/better-reflection/src/Reflector/ClassReflector.php:45 Roave\BetterReflection\SourceLocator\Type\MemoizingSourceLocator->locateIdentifier()
#7 phpstan-src/src/Reflection/BetterReflection/Reflector/MemoizingClassReflector.php:32 Roave\BetterReflection\Reflector\ClassReflector->reflect()
#8 phpstan-src/src/Reflection/BetterReflection/BetterReflectionProvider.php:118 PHPStan\Reflection\BetterReflection\Reflector\MemoizingClassReflector->reflect()
#9 phpstan-src/src/Reflection/ReflectionProvider/ChainReflectionProvider.php:30 PHPStan\Reflection\BetterReflection\BetterReflectionProvider->hasClass()
#10 phpstan-src/src/Reflection/ReflectionProvider/MemoizingReflectionProvider.php:37 PHPStan\Reflection\ReflectionProvider\ChainReflectionProvider->hasClass()
#11 phpstan-src/src/Broker/Broker.php:63 PHPStan\Reflection\ReflectionProvider\MemoizingReflectionProvider->hasClass()
#12 phpstan-src/src/Type/ObjectType.php:281 PHPStan\Broker\Broker->hasClass()
#13 phpstan-src/src/Type/VerbosityLevel.php:93 PHPStan\Type\ObjectType->PHPStan\Type\{closure}()
#14 phpstan-src/src/Type/ObjectType.php:297 PHPStan\Type\VerbosityLevel->handle()
#15 phpstan-src/src/Command/IgnoredRegexValidator.php:90 PHPStan\Type\ObjectType->describe()
#16 phpstan-src/src/Command/IgnoredRegexValidator.php:50 PHPStan\Command\IgnoredRegexValidator->getIgnoredTypes()
#17 phpstan-src/src/Analyser/IgnoredErrorHelper.php:89 PHPStan\Command\IgnoredRegexValidator->validate()
#18 phpstan-src/src/Command/AnalyseApplication.php:92 PHPStan\Analyser\IgnoredErrorHelper->initialize()
#19 phpstan-src/src/Command/AnalyseCommand.php:228 PHPStan\Command\AnalyseApplication->analyse()
#20 phpstan-src/vendor/symfony/console/Command/Command.php:255 PHPStan\Command\AnalyseCommand->execute()
#21 phpstan-src/vendor/symfony/console/Application.php:1009 Symfony\Component\Console\Command\Command->run()
#22 phpstan-src/vendor/symfony/console/Application.php:273 Symfony\Component\Console\Application->doRunCommand()
#23 phpstan-src/vendor/symfony/console/Application.php:149 Symfony\Component\Console\Application->doRun()
#24 phpstan-src/bin/phpstan(96): Symfony\Component\Console\Application->run()
#25 phpstan-src/bin/phpstan(97): {closure}()
The problem is here: https://github.com/phpstan/phpstan-src/blob/b9f1d99dcdb2dfc738f20ac1c6a579fe6c1cb16f/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php#L205
I added some debug statements and found that PCRE error was "Backtrack limit exhausted". We're on defaults, and it's 1000000 (same as on 7.4).
I had to set it to -1 to fix this. Here is the cause: https://gist.github.com/b1rdex/97698460e26b51f416b78d9c64b14bfd/7b9926f0c6e7f4363c3550b7b9ded8769903bd5d. It contains a very big heredoc.
The PCRE might be doing catastrophic backtracking. I can't fix it.
Please add some is_string() checks and report the error correctly.