Hello!

Summary

This PR introduces extension interfaces that allow PHPStan extensions to dynamically specify the $this context for closure parameters.

Problem

Currently, PHPStan only supports static @param-closure-this PHPDoc annotations, which cannot handle dynamic scenarios where the closure's $this type depends on runtime context. This particularly affects frameworks like PestPHP, which heavily rely on closures with dynamic $this bindings, and cannot properly communicate type information to PHPStan.

Real-world Example (PestPHP)

// PestPHP test file
test('user can login', function () {
    // PHPStan thinks $this is PHPUnit\Framework\TestCase (from @param-closure-this)
    // But it's actually the user's custom test class with additional methods
    $this->loginAs($user);  // <- PHPStan error: method not found
    $this->assertAuthenticated();
});

Solution

This PR adds three new extension interfaces that mirror the existing parameter type extensions:

• FunctionParameterClosureThisExtension - For function calls
• MethodParameterClosureThisExtension - For method calls
• StaticMethodParameterClosureThisExtension - For static method calls

These extensions can inspect the call context (AST nodes, scope, arguments) and return the appropriate $this type for the closure.

Implementation Details

Architecture

The implementation follows PHPStan's established patterns with minimal invasiveness:

1. Extension interfaces define the API for specifying closure $this types
2. Provider infrastructure manages and lazy-loads registered extensions
3. Integration in NodeScopeResolver checks extensions when processing closures
4. Service tags for DI registration: phpstan.functionParameterClosureThisExtension, etc.

Usage Example

Here's a psuedo-code example of how PestPHP could use this feature:

<?php
use PHPStan\Type\FunctionParameterClosureThisExtension;

class PestTestExtension implements FunctionParameterClosureThisExtension
{
    public function isFunctionSupported(FunctionReflection $function, ParameterReflection $parameter): bool
    {
        return in_array($function->getName(), ['test', 'it', 'beforeEach', 'afterEach'])
            && $parameter->getName() === 'closure';
    }

    public function getClosureThisTypeFromFunctionCall(FunctionReflection $function, FuncCall $call, ParameterReflection $parameter, Scope $scope): ?Type
    {
        // Detect the test class from file/namespace context
        $namespace = $scope->getNamespace();
        if ($namespace !== null && str_ends_with($namespace, '\\Tests')) {
            $testClass = $this->findTestClassInFile($scope->getFile());
            if ($testClass !== null) {
                return new ObjectType($testClass);
            }
        }

        return null;
    }
}

Register in phpstan.neon:

services:
  - class: PestTestExtension
    tags: [phpstan.functionParameterClosureThisExtension]

Thanks!