Allow ChildAdmin for Unidirectional References

[VincentLanglet]

Subject

Closes #7857.

Changing the typehint in the AbstractAdmin is BC.
But for the interface we'll have to wait next major (or should we consider the BC-break now @jordisala1991 ?)

Changelog

### Fixed
- Allow ChildAdmin for Unidirectional References

[VincentLanglet]

Static analysis tool are telling me that I'm calling

AdminInterface->setParent($child, null)

So either we ignore the error, either we consider the BC break in the interface.

Also, best would be to add a functional test

[jordisala1991]

IMHO, this patch should include:

• Tests about that feature (functional would be nice)
• Docs about this new way to add childs when they are null related in both ways.
• And it would be nice if we could detect when someone is passing null but he should pass an argument (not sure if that is possible).

[jordisala1991]

should we avoid call parent?

Something like

if $parent !== null $child->setParent()

[VincentLanglet]

Set parent is doing

final public function setParent(AdminInterface $parent, ?string $parentAssociationMapping): void
    {
        $this->parent = $parent;
        $this->parentAssociationMapping[$parent->getCode()] = $parentAssociationMapping;
    }

So, we still need to

• set the parent
• fill the parentAssociationMapping because later we acces it with

final public function getParentAssociationMapping(): ?string
    {
        if (!$this->isChild()) {
            throw new \LogicException(sprintf(
                'Admin "%s" has no parent.',
                static::class
            ));
        }

        $parent = $this->getParent()->getCode();

        return $this->parentAssociationMapping[$parent];
    }

which already accepts to return null.

[VincentLanglet]

• Tests about that feature (functional would be nice)

Done

• Docs about this new way to add childs when they are null related in both ways.

I don't think a lot of doc are needed, I added one line

• And it would be nice if we could detect when someone is passing null but he should pass an argument (not sure if that is possible).

Not possible IMHO. And technically you can decide to not pass a field even if it exists, for some reason...

The only issue I have now is the psalm/phpstan errors and if we should do a BC-break or not for this "fix".
WDYT ? Should we ignore the errors or update the interface ? @jordisala1991

[VincentLanglet]

I ignored the static analysis errors to avoid the bc break. But I'm pretty sure nobody are implementing the interface without extending the abstractAdmin ^^