Stop building show/list/form when accessing fieldDescription

[VincentLanglet]

Subject

I am targeting this branch, because I think I have found a BC-way to fix the bug (#6142) which can easily occur and create infinite loop.

Currently methods getFormFieldDescriptions, getFormFieldDescription and hasFormFieldDescription are calling this->buildForm.
But the buildForm method is calling lot of things, as shown in the issue, we may find

if (null !== $help) {
    $this->admin->getFormFieldDescription($name)->setHelp($help);
}

in the FormMapper->add, or

$formMapper->setHelps(['name' => 'help_page_name']);

in the SonataPageBundle configureFormField method witch lead to a hasFormFieldDescriptions call.

The developper could also possibly use the getFormFieldDescriptions, getFormFieldDescription and hasFormFieldDescription in the configureFormField and create an infinite loop.

Before we didn't try to build the form if the form was already build.
By adding a state, I now do not try to build the form if the build of the form already started.

Closes #6142.

Changelog

### Fixed
- `getFormFieldDescriptions`, `getFormFieldDescription` and `hasFormFieldDescription` doesn't build form anymore if the build already started, avoiding an infinite loop.
- `getShowFieldDescriptions`, `getShowFieldDescription` and `hasShowFieldDescription` doesn't build show anymore if the build already started, avoiding an infinite loop.
- `getListFieldDescriptions`, `getListFieldDescription` and `hasListFieldDescription` doesn't build list anymore if the build already started, avoiding an infinite loop.
- `getFilterFieldDescriptions`, `getFilterFieldDescription` and `hasFilterFieldDescription` doesn't build datagrid anymore if the build already started, avoiding an infinite loop.

[VincentLanglet]

@sonata-project/contributors I need your help on this !

[jordisala1991]

If the issue is not easily fixable, isnt it better to just revert your pr and then try to find a better way? to avoid breaking peoples apps.

[VincentLanglet]

If the issue is not easily fixable, isnt it better to just revert your pr and then try to find a better way? to avoid breaking peoples apps.

Yes, if I don't find better solution I will remove the buildXXX method only in getFormFieldDescription.

But the issue will still be present for others methods, it just not currently happen.

Currently SonataPageBundle call getFormFieldDescription('toto') during the configureFormField ; luckily it doesn't build the form. But if the call was made this way getFormFieldDescriptions['toto'] it would have create the same issue.

But I think I have find the right way to fix this definitely by adding a state.
I build the form only if I've not already started to build the form.
The same strategy was used for the menu or the routes.

[jordisala1991]

Looks ok to me, @gremo does it fix your issue?

[core23]

No tests required?

[VincentLanglet]

You want a functionnal test to prevent the infinite loop @core23 ?

[VincentLanglet]

Done @core23.

It was pretty useful since I caught a mistake. I wrote

$this->loaded['form']

instead of

$this->loaded['form'] = true

so the PR wasn't fixing the bug...

But everything is ok now.

[VincentLanglet]

Done @phansys

[core23]

Thanks @VincentLanglet