Symfony 4: Reusable code in "src" - php

Question

I'm trying to update a Symfony 3.4 application to Symfony 4. On my current applications I always share a local AdminBundle folder inside src. I know Symfony 4 recommends to be "bundle-less" now. But this AdminBundle is the base for most of my projects, and sometimes I make some updates to it that can be deployed to all my projects just pushing to the repository.
I tried to move by AdminBundle inside src but obviously that's not working. Could anyone detail the recipe or configuration needed to make this Bundle work under Symfony 4 in a generic way?
If this is not possible what's the best way to create a reusable code in symfony 4?

Answer 1

I'm currently using a similiar approach:
I've got a "CoreBundle" for shared Services, Entites, Subscribers etc under "src".
In order to make this usable i had to edit the following:
config/maker.yaml -> to use make:entity and create under CoreBundle
maker:
root_namespace: 'App\CoreBundle'
config/packages/doctrine.yaml modify -> to get the Entities from CoreBundle
orm:
auto_generate_proxy_classes: true
naming_strategy: doctrine.orm.naming_strategy.underscore_number_aware
auto_mapping: true
mappings:
App:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/CoreBundle/Entity'
prefix: 'App\CoreBundle\Entity'
alias: App
config/services.yaml add -> to import all SymfonyLike Classes
###> CoreBundle ###
App\CoreBundle\:
resource: '../src/CoreBundle/*'
exclude: '../src/CoreBundle/{DependencyInjection,Entity,Model,Migrations,Tests}'
App\CoreBundle\Controller\:
resource: '../src/CoreBundle/Controller'
tags: ['controller.service_arguments']
###< CoreBundle ###
config/* add -> where i wanted to import a separate config file
imports:
- { resource: '../../src/CoreBundle/Resources/config/*.yaml' }