[TASK] Let DataMapper::createEmptyObject() use doctrine/instantiator

During the removal of the ObjectManager (Extbase), the way the
DataMapper instantiates entities when thawing objects, i.e.
fetching a database row and transform it back into an entity
object, changed. doctrine/instantiator had been used to create
empty objects, i.e. creating objects without calling their
constructor. Now, entities with constructors cannot be thawed
any longer. To bring back this way of working (which existed
for as long as Extbase itself does), doctrine/instantiator is
brought back and used.

> composer req doctrine/instantiator:^2.0

Releases: main
Resolves: #100207
Related: #96208
Change-Id: Iabaddb2a027ea208c0eee75c26ea53f36e7e3285
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78051
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Daniel Goerz <daniel.goerz@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Daniel Goerz <daniel.goerz@b13.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>

composer.json

@@ -53,6 +53,7 @@
 		"doctrine/annotations": "^1.13.3 || ^2.0",
 		"doctrine/dbal": "^3.6.0",
 		"doctrine/event-manager": "^2.0",
+		"doctrine/instantiator": "^2.0",
 		"doctrine/lexer": "^2.0 || ^3.0",
 		"egulias/email-validator": "^4.0",
 		"enshrined/svg-sanitize": "^0.15.4",

typo3/sysext/core/Classes/Utility/GeneralUtility.php

@@ -2995,8 +2995,10 @@ public static function makeInstanceForDi(string $className, ...$constructorArgum
      *
      * @param class-string $className Base class name to evaluate
      * @return class-string Final class name to instantiate with `new [classname]`
+     * @internal This is not a public API method, do not use in own extensions.
+     *           Public to be accessible by extbase hydration.
      */
-    protected static function getClassName($className)
+    public static function getClassName($className)
     {
         if (class_exists($className)) {
             while (static::classHasImplementation($className)) {

typo3/sysext/core/Documentation/Changelog/12.4/Important-100207-LetDataMappercreateEmptyObjectUseDoctrineinstantiator.rst

@@ -0,0 +1,173 @@
+.. include:: /Includes.rst.txt
+
+.. _important-100207-1679414752:
+
+==================================================================================
+Important: #100207 - Let DataMapper::createEmptyObject() use doctrine/instantiator
+==================================================================================
+
+See :issue:`100207`
+
+Description
+===========
+
+Introduction
+------------
+
+This document explains the intended way in which the Extbase ORM thaws/hydrates objects.
+
+Hydrating Objects
+-----------------
+
+Hydrating (the term originates from `doctrine/orm`), or in Extbase terms thawing, is
+the act of creating an object from a given database row. The responsible class involved
+is the :php:`DataMapper`. During the process of hydrating, the :php:`DataMapper` creates
+objects to map the raw database data onto.
+
+Before diving into the framework internals, let's take a look at models from the
+users perspective.
+
+Creating Objects with Constructor Arguments
+-------------------------------------------
+
+Imagine you have a table `tx_extension_domain_model_blog` and a corresponding model
+or entity (entity is used as a synonym here) :php:`Vendor\Extension\Domain\Model\Blog`.
+
+Now, also imagine there is a domain rule which states, that all Blogs must have a
+title. This rule can easily be followed by letting the blog class have a constructor
+with a required argument :php:`string $title`.
+
+..  code-block:: php
+
+    class Blog extends AbstractEntity
+    {
+        protected ObjectStorage $posts;
+
+        public function __construct(protected string $title)
+        {
+            $this->posts = new ObjectStorage();
+        }
+    }
+
+This example also shows how the `posts` property is initialized. It is done in
+the constructor because PHP does not allow setting a default value that is of
+type object.
+
+Hydrating Objects with Constructor Arguments
+--------------------------------------------
+
+Whenever the user creates new blog objects in extension code, the aforementioned
+domain rule is followed. It's also possible to work on the `posts` `ObjectStorage`
+without further initialization. :php:`new Blog('title')` is all I need to create
+a blog object with a valid state.
+
+What happens in the :php:`DataMapper` however, is a totally different thing. When
+hydrating an object, the :php:`DataMapper` cannot follow any domain rules. Its only
+job is to map the raw database values onto a `Blog` instance. The :php:`DataMapper`
+could of course detect constructor arguments and try to guess which argument
+corresponds to what property but only if there is an easy mapping, i.e. if the
+constructor takes argument :php:`string $title` and updates property `title` with it.
+
+To avoid possible errors due to guessing, the :php:`DataMapper` simply
+ignores the constructor at all. It does so with the help of the library `doctrine/instantiator`.
+
+This pretty much explains the title of this document in detail. But there is more
+to all this.
+
+Initializing Objects
+--------------------
+
+Have a look at the :php:`$posts` property in the example above. If the :php:`DataMapper`
+ignores the constructor, that property is in an invalid state, i.e. uninitialized.
+
+To address this problem and possible others, the :php:`DataMapper` will call the method
+`initializeObject(): void` on models, if it exists.
+
+Here is an updated version of the model:
+
+..  code-block:: php
+
+    class Blog extends AbstractEntity
+    {
+        protected ObjectStorage $posts;
+
+        public function __construct(protected string $title)
+        {
+            $this->initializeObject();
+        }
+
+        public function initializeObject(): void
+        {
+            $this->posts = new ObjectStorage();
+        }
+    }
+
+This example demonstrates how Extbase expects the user to set up their model(s). If
+method :php:`initializeObject()` is used for initialization logic that needs to be
+triggered on initial creation AND on hydration. Please mind that :php:`__construct()`
+**SHOULD** call :php:`initializeObject()`.
+
+If there are no domain rules to follow, the recommended way to set up a model
+would then still be to define a :php:`__construct()` and :php:`initializeObject()`
+method like this:
+
+..  code-block:: php
+
+    class Blog extends AbstractEntity
+    {
+        protected ObjectStorage $posts;
+
+        public function __construct()
+        {
+            $this->initializeObject();
+        }
+
+        public function initializeObject(): void
+        {
+            $this->posts = new ObjectStorage();
+        }
+    }
+
+Mutating Objects
+----------------
+
+I'd like to add a few more words on mutators (setter, adder, etc.). One might think that
+:php:`DataMapper` uses mutators during object hydration but it DOES NOT. `mutators`
+are the only way for the user (developer) to implement business rules besides
+using the constructor.
+
+The :php:`DataMapper` uses `@internal` method :php:`AbstractDomainObject::_setProperty()`
+to update object properties. This looks a bit dirty and is a way around all business
+rules but that's what the :php:`DataMapper` needs in order to leave the `mutators` to
+the users.
+
+..  warning::
+
+    While :php:`DataMapper` does not use any mutators, other parts of Extbase do.
+    Both, validation and property mapping, either use existing mutators or gather
+    type information from them. This will change in the future but as of TYPO3 12 LTS
+    this information is correct.
+
+Property Visibility
+-------------------
+
+One important thing to know is that Extbase needs entity properties to be protected
+or public. As written in the former paragraph, :php:`AbstractDomainObject::_setProperty()`
+is used to bypass setters. :php:`AbstractDomainObject` however, is not able to access
+private properties of child classes, hence the need to have protected or public
+properties.
+
+
+Dependency Injection
+--------------------
+
+Without digging too deep into this topic the following statements have to be made.
+Extbase expects entities to be so called prototypes, i.e. classes that do have a
+different state per instance. DataMapper DOES NOT use Dependency Injection for the
+creation of entities, i.e. it does not query the object container. This also means,
+that Dependency Injection is not possible in entities.
+
+If you think that your entities need to use/access services, you need to find other
+ways to implement it.
+
+.. index:: PHP-API, ext:extbase