[Form] DateTimeType ignores date_format and forces html5 format

[spantaleev]

When a single_text datetime widget is created with a custom date_format, it gets ignored and the HTML5 format gets used.

This is because:

• in setDefaultOptions(), the default for format is set to the HTML5 format
• in buildForm(), for single_text widgets, the DateTimeToRfc3339Transformer is used, because the default option for format is the HTML5 format. The date_format option is completely ignored

The documentation for the datetime form type is very confusing. This form type uses both format and date_format, but the documentation does not mention anything about a format option.
Only the date_format option is documented, and its description links to the documentation for format on the date widget.

Broken code:

//`date_format` is ignored. `format` is used (defaults to the HTML5 format)
$builder->add('field', 'datetime', array(
    'widget' => 'single_text',
    'date_format' => 'CUSTOM'
));

Working code:

//The CUSTOM format is used (overrides the default `format` HTML5 value)
$builder->add('field', 'datetime', array(
    'widget' => 'single_text',
    'format' => 'CUSTOM'
));

Perhaps date_format should be removed completely and format should be documented.

This affects Symfony 2.1 and most likely 2.2 as well (judging by the code).