PHPStan - PHP Static Analysis Tool (Discover Bugs In Your Code Without Running It!)

PHPStan focuses on finding errors in your code without actually running it. It catches whole classes of bugs even before you write tests for the code. It moves PHP closer to compiled languages in the sense that the correctness of each line of the code can be checked before you run the actual line.

Read more about PHPStan on Medium.com
Try out PHPStan on the on-line playground!

Prerequisites
PHPStan requires PHP >= 7.1. You have to run it in environment with PHP 7.x but the actual code does not have to use PHP 7.x features. (Code written for PHP 5.6 and earlier can run on 7.x mostly unmodified.)
PHPStan works best with modern object-oriented code. The more strongly-typed your code is, the more information you give PHPStan to work with.
Properly annotated and typehinted code (class properties, function and method arguments, return types) helps not only static analysis tools but also other people that work with the code to understand it.

Installation
To start performing analysis on your code, require PHPStan in Composer:

composer require --dev phpstan/phpstan

Composer will install PHPStan's executable in its bin-dir which defaults to vendor/bin.
If you have conflicting dependencies or you want to install PHPStan globally, the best way is via a PHAR archive. You will always find the latest stable PHAR archive below the release notes. You can also use the phpstan/phpstan-shim package to install PHPStan via Composer without the risk of conflicting dependencies.
You can also use PHPStan via Docker.

First run
To let PHPStan analyse your codebase, you have to use the analyse command and point it to the right directories.
So, for example if you have your classes in directories src and tests, you can run PHPStan like this:

vendor/bin/phpstan analyse src tests

PHPStan will probably find some errors, but don't worry, your code might be just fine. Errors found on the first run tend to be:

Extra arguments passed to functions (e. g. function requires two arguments, the code passes three)
Extra arguments passed to print/sprintf functions (e. g. format string contains one placeholder, the code passes two values to replace)
Obvious errors in dead code
Magic behaviour that needs to be defined. See Extensibility.

After fixing the obvious mistakes in the code, look to the following section for all the configuration options that will bring the number of reported errors to zero making PHPStan suitable to run as part of your continuous integration script.

Rule levels
If you want to use PHPStan but your codebase isn't up to speed with strong typing and PHPStan's strict checks, you can choose from currently 8 levels (0 is the loosest and 7 is the strictest) by passing --level to analyse command. Default level is 0.
This feature enables incremental adoption of PHPStan checks. You can start using PHPStan with a lower rule level and increase it when you feel like it.
You can also use --level max as an alias for the highest level. This will ensure that you will always use the highest level when upgrading to new versions of PHPStan. Please note that this can create a significant obstacle when upgrading to a newer version because you might have to fix a lot of code to bring the number of errors down to zero.

Extensibility
Unique feature of PHPStan is the ability to define and statically check "magic" behaviour of classes - accessing properties that are not defined in the class but are created in __get and __set and invoking methods using __call.
See Class reflection extensions, Dynamic return type extensions and Type-specifying extensions.
You can also install official framework-specific extensions:

Unofficial extensions for other frameworks and libraries are also available:

Unofficial extensions with third-party rules:

New extensions are becoming available on a regular basis!

Configuration
Config file is passed to the phpstan executable with -c option:

vendor/bin/phpstan analyse -l 4 -c phpstan.neon src tests

When using a custom project config file, you have to pass the --level (-l) option to analyse command (default value does not apply here).
If you do not provide config file explicitly, PHPStan will look for files named phpstan.neon or phpstan.neon.dist in current directory.
The resolution priority is as such:

If config file is provided on command line, it is used.
If config file phpstan.neon exists in current directory, it will be used.
If config file phpstan.neon.dist exists in current directory, it will be used.
If none of the above is true, no config will be used.

NEON file format is very similar to YAML. All the following options are part of the parameters section.

Configuration variables

%rootDir% - root directory where PHPStan resides (i.e. vendor/phpstan/phpstan in Composer installation)
%currentWorkingDirectory% - current working directory where PHPStan was executed

Configuration options

tmpDir - specifies the temporary directory used by PHPStan cache (defaults to sys_get_temp_dir() . '/phpstan')
level - specifies analysis level - if specified, -l option is not required
paths - specifies analysed paths - if specified, paths are not required to be passed as arguments

Autoloading
PHPStan uses Composer autoloader so the easiest way how to autoload classes is through the autoload/autoload-dev sections in composer.json.

Specify paths to scan
If PHPStan complains about some non-existent classes and you're sure the classes exist in the codebase AND you don't want to use Composer autoloader for some reason, you can specify directories to scan and concrete files to include using autoload_directories and autoload_files array parameters:

parameters:
 autoload_directories:
  - %rootDir%/../../../build
 autoload_files:
  - %rootDir%/../../../generated/routes/GeneratedRouteList.php

%rootDir% is expanded to the root directory where PHPStan resides.

Autoloading for global installation
PHPStan supports global installation using composer global or via a PHAR archive. In this case, it's not part of the project autoloader, but it supports autodiscovery of the Composer autoloader from current working directory residing in vendor/:

cd /path/to/project
phpstan analyse src tests # looks for autoloader at /path/to/project/vendor/autoload.php

If you have your dependencies installed at a different path or you're running PHPStan from a different directory, you can specify the path to the autoloader with the --autoload-file|-a option:

phpstan analyse --autoload-file=/path/to/autoload.php src tests

Exclude files from analysis
If your codebase contains some files that are broken on purpose (e. g. to test behaviour of your application on files with invalid PHP code), you can exclude them using the excludes_analyse array parameter. String at each line is used as a pattern for the fnmatch function.

parameters:
 excludes_analyse:
  - %rootDir%/../../../tests/*/data/*

Include custom extensions
If your codebase contains php files with extensions other than the standard .php extension then you can add them to the fileExtensions array parameter:

parameters:
 fileExtensions:
  - php
  - module
  - inc

Universal object crates
Classes without predefined structure are common in PHP applications. They are used as universal holders of data - any property can be set and read on them. Notable examples include stdClass, SimpleXMLElement (these are enabled by default), objects with results of database queries etc. Use universalObjectCratesClasses array parameter to let PHPStan know which classes with these characteristics are used in your codebase:

parameters:
 universalObjectCratesClasses:
  - Dibi\Row
  - Ratchet\ConnectionInterface

Add non-obviously assigned variables to scope
If you use some variables from a try block in your catch blocks, set polluteCatchScopeWithTryAssignments boolean parameter to true.

try {
 $author = $this->getLoggedInUser();
 $post = $this->postRepository->getById($id);
} catch (PostNotFoundException $e) {
 // $author is probably defined here
 throw new ArticleByAuthorCannotBePublished($author);
}

If you are enumerating over all possible situations in if-elseif branches and PHPStan complains about undefined variables after the conditions, you can write an else branch with throwing an exception:

if (somethingIsTrue()) {
 $foo = true;
} elseif (orSomethingElseIsTrue()) {
 $foo = false;
} else {
 throw new ShouldNotHappenException();
}

doFoo($foo);

I recommend leaving polluteCatchScopeWithTryAssignments set to false because it leads to a clearer and more maintainable code.

Custom early terminating method calls
Previous example showed that if a condition branches end with throwing an exception, that branch does not have to define a variable used after the condition branches end.
But exceptions are not the only way how to terminate execution of a method early. Some specific method calls can be perceived by project developers also as early terminating - like a redirect() that stops execution by throwing an internal exception.

if (somethingIsTrue()) {
 $foo = true;
} elseif (orSomethingElseIsTrue()) {
 $foo = false;
} else {
 $this->redirect('homepage');
}

doFoo($foo);

These methods can be configured by specifying a class on whose instance they are called like this:

parameters:
 earlyTerminatingMethodCalls:
  Nette\Application\UI\Presenter:
   - redirect
   - redirectUrl
   - sendJson
   - sendResponse

Ignore error messages with regular expressions
If some issue in your code base is not easy to fix or just simply want to deal with it later, you can exclude error messages from the analysis result with regular expressions:

parameters:
 ignoreErrors:
  - '#Call to an undefined method [a-zA-Z0-9\\_]+::method\(\)#'
  - '#Call to an undefined method [a-zA-Z0-9\\_]+::expects\(\)#'
  - '#Access to an undefined property PHPUnit_Framework_MockObject_MockObject::\$[a-zA-Z0-9_]+#'
  - '#Call to an undefined method PHPUnit_Framework_MockObject_MockObject::[a-zA-Z0-9_]+\(\)#'

To exclude an error in a specific directory or file, specify a path or paths along with the message:

parameters:
 ignoreErrors:
  -
   message: '#Call to an undefined method [a-zA-Z0-9\\_]+::method\(\)#'
   path: %currentWorkingDirectory%/some/dir/SomeFile.php
  -
   message: '#Call to an undefined method [a-zA-Z0-9\\_]+::method\(\)#'
   paths:
    - %currentWorkingDirectory%/some/dir/*
    - %currentWorkingDirectory%/other/dir/*
  - '#Other error to catch anywhere#'

If some of the patterns do not occur in the result anymore, PHPStan will let you know and you will have to remove the pattern from the configuration. You can turn off this behaviour by setting reportUnmatchedIgnoredErrors to false in PHPStan configuration.

Bootstrap file
If you need to initialize something in PHP runtime before PHPStan runs (like your own autoloader), you can provide your own bootstrap file:

parameters:
 bootstrap: %rootDir%/../../../phpstan-bootstrap.php

Custom rules
PHPStan allows writing custom rules to check for specific situations in your own codebase. Your rule class needs to implement the PHPStan\Rules\Rule interface and registered as a service in the configuration file:

services:
 -
  class: MyApp\PHPStan\Rules\DefaultValueTypesAssignedToPropertiesRule
  tags:
   - phpstan.rules.rule

For inspiration on how to implement a rule turn to src/Rules to see a lot of built-in rules.
Check out also phpstan-strict-rules repository for extra strict and opinionated rules for PHPStan!
Check as well phpstan-deprecation-rules for rules that detect usage of deprecated classes, methods, properties, constants and traits!

Custom error formatters
PHPStan outputs errors via formatters. You can customize the output by implementing the ErrorFormatter interface in a new class and add it to the configuration. For existing formatters, see next chapter.

interface ErrorFormatter
{

 /**
  * Formats the errors and outputs them to the console.
  *
  * @param \PHPStan\Command\AnalysisResult $analysisResult
  * @param \Symfony\Component\Console\Style\OutputStyle $style
  * @return int Error code.
  */
 public function formatErrors(
  AnalysisResult $analysisResult,
  \Symfony\Component\Console\Style\OutputStyle $style
 ): int;

}

services:
 errorFormatter.awesome:
  class: App\PHPStan\AwesomeErrorFormatter

Use the name part after errorFormatter. as the CLI option value:

vendor/bin/phpstan analyse -c phpstan.neon -l 4 --error-format awesome src tests

Existing error formatters to be used
You can pass the following keywords to the --error-format=X parameter in order to affect the output:

table: Default. Grouped errors by file, colorized. For human consumption.
raw: Contains one error per line, with path to file, line number, and error description
checkstyle: Creates a checkstyle.xml compatible output. Note that you'd have to redirect output into a file in order to capture the results for later processing.
json: Creates minified .json output without whitespaces. Note that you'd have to redirect output into a file in order to capture the results for later processing.
prettyJson: Creates human readable .json output with whitespaces and indentations. Note that you'd have to redirect output into a file in order to capture the results for later processing.

Class reflection extensions
Classes in PHP can expose "magical" properties and methods decided in run-time using class methods like __get, __set and __call. Because PHPStan is all about static analysis (testing code for errors without running it), it has to know about those properties and methods beforehand.
When PHPStan stumbles upon a property or a method that is unknown to built-in class reflection, it iterates over all registered class reflection extensions until it finds one that defines the property or method.
Class reflection extension cannot have PHPStan\Broker\Broker (service for obtaining class reflections) injected in the constructor due to circular reference issue, but the extensions can implement PHPStan\Reflection\BrokerAwareExtension interface to obtain Broker via a setter.

Properties class reflection extensions
This extension type must implement the following interface:

namespace PHPStan\Reflection;

interface PropertiesClassReflectionExtension
{

 public function hasProperty(ClassReflection $classReflection, string $propertyName): bool;

 public function getProperty(ClassReflection $classReflection, string $propertyName): PropertyReflection;

}

Most likely you will also have to implement a new PropertyReflection class:

namespace PHPStan\Reflection;

interface PropertyReflection
{

 public function getType(): Type;

 public function getDeclaringClass(): ClassReflection;

 public function isStatic(): bool;

 public function isPrivate(): bool;

 public function isPublic(): bool;

}

This is how you register the extension in project's PHPStan config file:

services:
 -
  class: App\PHPStan\PropertiesFromAnnotationsClassReflectionExtension
  tags:
   - phpstan.broker.propertiesClassReflectionExtension

Methods class reflection extensions
This extension type must implement the following interface:

namespace PHPStan\Reflection;

interface MethodsClassReflectionExtension
{

 public function hasMethod(ClassReflection $classReflection, string $methodName): bool;

 public function getMethod(ClassReflection $classReflection, string $methodName): MethodReflection;

}

Most likely you will also have to implement a new MethodReflection class:

namespace PHPStan\Reflection;

interface MethodReflection
{

 public function getDeclaringClass(): ClassReflection;

 public function getPrototype(): self;

 public function isStatic(): bool;

 public function isPrivate(): bool;

 public function isPublic(): bool;

 public function getName(): string;

 /**
  * @return \PHPStan\Reflection\ParameterReflection[]
  */
 public function getParameters(): array;

 public function isVariadic(): bool;

 public function getReturnType(): Type;

}

This is how you register the extension in project's PHPStan config file:

services:
 -
  class: App\PHPStan\EnumMethodsClassReflectionExtension
  tags:
   - phpstan.broker.methodsClassReflectionExtension

Dynamic return type extensions
If the return type of a method is not always the same, but depends on an argument passed to the method, you can specify the return type by writing and registering an extension.
Because you have to write the code with the type-resolving logic, it can be as complex as you want.
After writing the sample extension, the variable $mergedArticle will have the correct type:

$mergedArticle = $this->entityManager->merge($article);
// $mergedArticle will have the same type as $article

This is the interface for dynamic return type extension:

namespace PHPStan\Type;

use PhpParser\Node\Expr\MethodCall;
use PHPStan\Analyser\Scope;
use PHPStan\Reflection\MethodReflection;

interface DynamicMethodReturnTypeExtension
{

 public function getClass(): string;

 public function isMethodSupported(MethodReflection $methodReflection): bool;

 public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type;

}

And this is how you'd write the extension that correctly resolves the EntityManager::merge() return type:

public function getClass(): string
{
 return \Doctrine\ORM\EntityManager::class;
}

public function isMethodSupported(MethodReflection $methodReflection): bool
{
 return $methodReflection->getName() === 'merge';
}

public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type
{
 if (count($methodCall->args) === 0) {
  return \PHPStan\Reflection\ParametersAcceptorSelector::selectFromArgs(
   $scope,
   $methodCall->args,
   $methodReflection->getVariants()
  )->getReturnType();
 }
 $arg = $methodCall->args[0]->value;

 return $scope->getType($arg);
}

And finally, register the extension to PHPStan in the project's config file:

services:
 -
  class: App\PHPStan\EntityManagerDynamicReturnTypeExtension
  tags:
   - phpstan.broker.dynamicMethodReturnTypeExtension

There's also an analogous functionality for:

static methods using DynamicStaticMethodReturnTypeExtension interface and phpstan.broker.dynamicStaticMethodReturnTypeExtension service tag.
functions using DynamicFunctionReturnTypeExtension interface and phpstan.broker.dynamicFunctionReturnTypeExtension service tag.

Type-specifying extensions
These extensions allow you to specify types of expressions based on certain pre-existing conditions. This is best illustrated with couple examples:

if (is_int($variable)) {
    // here we can be sure that $variable is integer
}

// using PHPUnit's asserts

self::assertNotNull($variable);
// here we can be sure that $variable is not null

Type-specifying extension cannot have PHPStan\Analyser\TypeSpecifier injected in the constructor due to circular reference issue, but the extensions can implement PHPStan\Analyser\TypeSpecifierAwareExtension interface to obtain TypeSpecifier via a setter.
This is the interface for type-specifying extension:

namespace PHPStan\Type;

use PhpParser\Node\Expr\StaticCall;
use PHPStan\Analyser\Scope;
use PHPStan\Analyser\SpecifiedTypes;
use PHPStan\Analyser\TypeSpecifierContext;
use PHPStan\Reflection\MethodReflection;

interface StaticMethodTypeSpecifyingExtension
{

 public function getClass(): string;

 public function isStaticMethodSupported(MethodReflection $staticMethodReflection, StaticCall $node, TypeSpecifierContext $context): bool;

 public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes;

}

And this is how you'd write the extension for the second example above:

public function getClass(): string
{
 return \PHPUnit\Framework\Assert::class;
}

public function isStaticMethodSupported(MethodReflection $staticMethodReflection, StaticCall $node, TypeSpecifierContext $context): bool;
{
 // The $context argument tells us if we're in an if condition or not (as in this case).
 return $staticMethodReflection->getName() === 'assertNotNull' && $context->null();
}

public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
{
 // Assuming extension implements \PHPStan\Analyser\TypeSpecifierAwareExtension.
 return $this->typeSpecifier->create($node->var, \PHPStan\Type\TypeCombinator::removeNull($scope->getType($node->var)), $context);
}

And finally, register the extension to PHPStan in the project's config file:

services:
 -
  class: App\PHPStan\AssertNotNullTypeSpecifyingExtension
  tags:
   - phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension

There's also an analogous functionality for:

dynamic methods using MethodTypeSpecifyingExtension interface and phpstan.typeSpecifier.methodTypeSpecifyingExtension service tag.
functions using FunctionTypeSpecifyingExtension interface and phpstan.typeSpecifier.functionTypeSpecifyingExtension service tag.

Building
You can either run the whole build including linting and coding standards using