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+# CLAUDE.md
+
+This file provides guidance for AI assistants working with the phpstan/phpstan-phpunit repository.
+
+## Project Overview
+
+This is a PHPStan extension that provides advanced static analysis support for PHPUnit test suites. It offers:
+
+- **Type extensions**: Correct return types for `createMock()`, `getMockForAbstractClass()`, `getMockFromWsdl()`, `MockBuilder::getMock()`, etc., returning intersection types (e.g., `MockObject&Foo`) so both mock and original class methods are available.
+- **PHPDoc interpretation**: Converts `Foo|MockObject` union types in phpDocs to intersection types.
+- **Assert type narrowing**: Specifies types of expressions passed to `assertInstanceOf`, `assertTrue`, `assertInternalType`, etc.
+- **Early terminating methods**: Defines `fail()`, `markTestIncomplete()`, `markTestSkipped()` as early terminating to prevent false positive undefined variable errors.
+- **Strict rules** (in `rules.neon`): Checks for better assertion usage (e.g., prefer `assertTrue()` over `assertSame(true, ...)`), `@covers` validation, data provider declaration checks, and more.
+
+## PHP Version Requirements
+
+This repository supports **PHP 7.4+**. Do not use language features unavailable in PHP 7.4 (e.g., enums, fibers, readonly properties, intersection types in code — though they appear in stubs/phpDocs).
+
+## PHPUnit Compatibility
+
+The extension supports multiple PHPUnit versions: **^9.5, ^10.5, ^11.5, ^12.0**. Code must be compatible across all these versions. The CI matrix tests all combinations.
+
+## Common Commands
+
+```bash
+# Install dependencies
+composer install
+
+# Run all checks (lint, coding standard, tests, PHPStan)
+make check
+
+# Run tests only
+make tests
+
+# Run PHPStan analysis
+make phpstan
+
+# Run linting
+make lint
+
+# Install coding standard tool (first time only)
+make cs-install
+
+# Run coding standard checks
+make cs
+
+# Fix coding standard issues
+make cs-fix
+
+# Generate PHPStan baseline
+make phpstan-generate-baseline
+```
+
+## Project Structure
+
+```
+src/
+├── PhpDoc/PHPUnit/          # PHPDoc type resolution extensions
+├── Rules/PHPUnit/           # Static analysis rules for PHPUnit
+└── Type/PHPUnit/            # Type-specifying and dynamic return type extensions
+    └── Assert/              # Assert method type narrowing
+
+tests/
+├── Rules/PHPUnit/           # Rule tests and test data (data/ subdirectory)
+├── Rules/Methods/           # Method call rule tests
+├── Type/PHPUnit/            # Type extension tests and test data (data/ subdirectory)
+└── bootstrap.php            # Test bootstrap (loads Composer autoloader)
+
+stubs/                       # PHPUnit stub files for type definitions
+```
+
+## Configuration Files
+
+- **`extension.neon`** — Main extension configuration registered via phpstan/extension-installer. Defines parameters, services (type extensions, helpers), and stub files.
+- **`rules.neon`** — Strict PHPUnit-specific rules. Loaded separately; users opt in by including this file.
+- **`phpstan.neon`** — Self-analysis configuration (level 8, with strict rules and deprecation rules).
+- **`phpstan-baseline.neon`** — Baseline for known PHPStan errors in the project itself.
+- **`phpunit.xml`** — PHPUnit configuration for running the test suite.
+
+## Architecture
+
+### Type Extensions (`src/Type/PHPUnit/`)
+
+These implement PHPStan interfaces to provide correct types:
+
+- `MockBuilderDynamicReturnTypeExtension` — Preserves `MockBuilder<T>` generic type through chained method calls.
+- `MockForIntersectionDynamicReturnTypeExtension` — Returns `MockObject&T` intersection types for mock creation methods.
+- `Assert/AssertMethodTypeSpecifyingExtension` (and function/static variants) — Narrows types after assert calls (e.g., after `assertInstanceOf(Foo::class, $x)`, `$x` is known to be `Foo`).
+
+### Rules (`src/Rules/PHPUnit/`)
+
+These implement `PHPStan\Rules\Rule<T>` to report errors:
+
+- `AssertSameBooleanExpectedRule`, `AssertSameNullExpectedRule` — Suggest specific assertions over generic `assertSame`.
+- `AssertSameWithCountRule` — Suggest `assertCount()` over `assertSame(count(...), ...)`.
+- `ClassCoversExistsRule`, `ClassMethodCoversExistsRule` — Validate `@covers` annotations reference existing code.
+- `DataProviderDeclarationRule`, `DataProviderDataRule` — Validate data provider declarations and data.
+- `MockMethodCallRule` — Check mock method calls are valid.
+- `ShouldCallParentMethodsRule` — Verify `setUp()`/`tearDown()` call parent methods.
+
+### Stubs (`stubs/`)
+
+PHPStan stub files that provide generic type information for PHPUnit classes (e.g., `TestCase::createMock<T>()` returns `MockObject&T`).
+
+## Writing Tests
+
+- **Rule tests** extend `PHPStan\Testing\RuleTestCase<T>`. They implement `getRule()` and call `$this->analyse()` with a test data file path and expected errors array. Test data files live in `tests/Rules/PHPUnit/data/`.
+- **Type tests** extend `PHPStan\Testing\TypeInferenceTestCase`. They use `@dataProvider` with `self::gatherAssertTypes()` or `self::dataFileAsserts()` and call `$this->assertFileAsserts()`. Test data files live in `tests/Type/PHPUnit/data/`.
+- Both types override `getAdditionalConfigFiles()` to return the path to `extension.neon` (and sometimes `rules.neon`).
+
+## Coding Standards
+
+- Uses tabs for indentation (PHP, XML, NEON files).
+- Uses spaces for YAML files (indent size 2).
+- Coding standard is enforced via [phpstan/build-cs](https://github.com/phpstan/build-cs) (PHPCS with a custom standard).
+- Run `make cs` to check, `make cs-fix` to auto-fix.
+
+## CI Pipeline
+
+The GitHub Actions workflow (`.github/workflows/build.yml`) runs on the `2.0.x` branch and pull requests:
+
+1. **Lint** — PHP syntax check across PHP 7.4–8.5.
+2. **Coding Standard** — PHPCS checks using build-cs.
+3. **Tests** — PHPUnit across PHP 7.4–8.5 × lowest/highest dependencies × PHPUnit 9.5/10.5/11.5/12.0 (with version-appropriate exclusions).
+4. **Static Analysis** — PHPStan self-analysis with the same matrix.
+5. **Mutation Testing** — Infection framework on PHP 8.2–8.5, requires 100% MSI on changed lines.
+
+## Development Branch
+
+The main development branch is `2.0.x`.