[Form] [DataMapper] Read only form datamapper fix

[Romain-Geissler]

The current 2.0.13 Symfony\Component\Form\Extension\Core\DataMapper\PropertyPathMapper enables to overwrite data from form values, no matter the form fields are read only or not.

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: -
Todo: -
License of the code: MIT
Documentation PR: -

[travisbot]

This pull request passes (merged 47605f6 into 72b2f69).

[webmozart]

Forms don't bind when they are read only, so why is this change necessary?

[stof]

@bschussek A read-only child will not be bound but the setter will still be called on the parent object for this field (with the old value), making it mandatory to define setters for read-only fields.

[Romain-Geissler]

In my case, the property is still set through a setter even if the field for this property is read only. The problem is the setter is not called with the legacy value it held, but with the value given by the form. In my case the value is transformed from a string to an object by a DataMapper, which returns null for an empty string/value. Thus, the setter is called with null instead of the previous non null value (and not always the same) it held.

This PR just prevent the setter for an object property marked as read only in the form definition from being called.

[webmozart]

Ok, 👍 then