Summary

Adds a PHP configuration format as a first-class alternative to YAML, designed to become the canonical way to configure Codeception in future versions. A codeception.php (or *.suite.php / env file) returns a fluent builder — or a raw array — instead of YAML. This unlocks IDE autocomplete, PHPStan-checkable config, ::class constants, native getenv(), and real PHP expressions (E_ALL & ~E_DEPRECATED), while keeping a 1:1 mapping to every existing YAML key. YAML is untouched and remains the default — the PHP format is fully opt-in.

<?php
use Codeception\Config\GlobalConfig;
use Codeception\Config\SuiteConfig;

return GlobalConfig::create()
    ->namespace('App\Tests')
    ->paths(tests: 'tests', output: 'tests/_output', data: 'tests/_data', support: 'tests/Support')
    ->settings(colors: true, memoryLimit: '1024M')
    ->suite('Functional', SuiteConfig::create()
        ->actor('FunctionalTester')
        ->module('Asserts')
        ->module('Db', ['dsn' => getenv('DB_DSN')]));

What's new

Builder API (src/Codeception/Config/, namespace Codeception\Config\):

• GlobalConfig, SuiteConfig (both final), ConfigInterface (forever-contract = toArray() only), AbstractConfigBuilder (@internal), Params.
• Uniform pattern: singular appenders (module(), moduleConfig(), extension(), suite(), env(), commands()) + one raw escape hatch merge(). settings() uses explicit named nullable params (camelCase → snake_case) for autocomplete.

Loader (Configuration.php): per role (global / suite / env), if any .php variant exists, PHP wins and YAML is ignored — one rule everywhere. Config files are loaded exactly once, inside an isolated closure wrapped in output buffering (stray echo can't corrupt --xml/--json output), with concrete-type guards (a SuiteConfig returned in global position throws a clear error naming the file and expected type). Cross-format extends works both directions.

Params: %param% stays YAML-only; PHP configs use getenv() in the global file and Params::get() in suite/env files (with a self-explaining exception if Params::get() is called too early during global load).

Tooling & scaffolding:

• config:validate now reports the loaded config file path.
• config:to-php — new command migrating existing YAML projects to builder-style PHP (--dry-run prints without writing; renderer Lib/Generator/PhpConfigFile.php).
• bootstrap, init, g:suite, g:env gain PHP output; g:suite/g:env detect the project format and no longer risk generating a silently-shadowed file when the other extension already exists.

Design notes

• New Codeception\Config\ namespace deliberately avoids colliding with the existing Codeception\Configuration class.
• A reflection drift-guard test fails if any core $defaultConfig / $defaultSuiteSettings key gains no builder method — the canonical API can't silently lag core.
• Mutable builders (matching Rector / PHP-CS-Fixer); merge() renamed from with() since with* implies immutable clone in PHP.
• Considered and rejected: closure-style config, attributes, immutable builders, a separate lib-config package, var_export array generation. (Rationale available on request.)

Backward compatibility

Non-breaking and additive. YAML behavior is unchanged; YAML remains the default scaffold. Flipping the default to PHP, and any future YAML deprecation, is left as a maintainer decision — not smuggled in here.

Tests

• 30 unit tests (tests/unit/Codeception/Config/): every builder method → expected key/value, snake_case mapping, guards, merge() order, drift-guards, Params::get() timing.
• 13 cli tests (tests/cli/ConfigPhpFormatCest.php): discovery, php-wins, env-wins, cross-format extends, type/echo/invalid-return errors, inline-suite shadowing, config:to-php migrate → build → run.
• Verified against a CI-faithful Linux run (build + web server + run cli,unit,coverage), plus phpstan analyse src and composer cs-tests clean.

Unrelated changes (disclosed)

This commit also bumps CI actions: actions/checkout@v6 → v7 and actions/cache@v3 → v6 in .github/workflows/build.yml. Not history-rewritten; called out here for review.