Custom Acme namespaces with Symfony Flex

composer.json

{
    "type": "project",
    "license": "proprietary",
    "require": {
        "php": "^7.1.3",
        "ext-iconv": "*",
        "symfony/console": "^4.0",
        "symfony/flex": "^1.0",
        "symfony/framework-bundle": "^4.0",
        "symfony/lts": "^4@dev",
        "symfony/yaml": "^4.0"
    },
    "require-dev": {
        "symfony/dotenv": "^4.0"
    },
    "config": {
        "preferred-install": {
            "*": "dist"
        },
        "sort-packages": true
    },
    "autoload": {
        "psr-4": {
            "App\\": "src/App/",
            "Acme\\": "src/Acme/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "App\\Tests\\": "tests/"
        }
    },
    "replace": {
        "symfony/polyfill-iconv": "*",
        "symfony/polyfill-php71": "*",
        "symfony/polyfill-php70": "*",
        "symfony/polyfill-php56": "*"
    },
    "scripts": {
        "auto-scripts": {
            "cache:clear": "symfony-cmd",
            "assets:install --symlink --relative %PUBLIC_DIR%": "symfony-cmd"
        },
        "post-install-cmd": [
            "@auto-scripts"
        ],
        "post-update-cmd": [
            "@auto-scripts"
        ]
    },
    "conflict": {
        "symfony/symfony": "*"
    },
    "extra": {
        "symfony": {
            "id": "01C8D4KZZ4TAGW8JM3F94XV9WQ",
            "allow-contrib": false
        }
    }
}

services.yml

# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration
parameters:

services:
    # default configuration for services in *this* file
    _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
        public: false       # Allows optimizing the container by removing unused services; this also means
                            # fetching services directly from the container via $container->get() won't work.
                            # The best practice is to be explicit about your dependencies anyway.

    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/App/*'
        exclude: '../src/App/{Entity,Migrations,Tests,Kernel.php}'

    Acme\:
        resource: '../src/Acme/*'
        exclude: '../src/Acme/{Entity,Migrations,Tests,Kernel.php}'

    # controllers are imported separately to make sure services can be injected
    # as action arguments even if you don't extend any base controller class
    App\Controller\:
        resource: '../src/App/Controller'
        tags: ['controller.service_arguments']

    Acme\Presentation\Controller\:    
        resource: '../src/Acme/Presentation/Controller'
        tags: ['controller.service_arguments']

    # add more service definitions when explicit configuration is needed
    # please note that last definitions always *replace* previous ones

My (Domain-Driven Design) directory structure:

src/App/Controller
src/Acme/Application/Service
src/Acme/Domain/Model
src/Acme/Infrastructure
src/Acme/Presentation/Controller

As described by @predakanga:

• symfony/flex#93 (comment)

Further discussions:

• symfony/flex#196
• symfony/flex#138
• symfony/maker-bundle#2