UPGRADE FROM 3.0 to 3.1

DependencyInjection

Using unsupported configuration keys in YAML configuration files has been deprecated and will raise an exception in Symfony 4.0.
Using unsupported options to configure service aliases has been deprecated and will raise an exception in Symfony 4.0.

The choices_as_values option of the ChoiceType has been deprecated and will be removed in Symfony 4.0.
Support for data objects that implements both Traversable and ArrayAccess in ResizeFormListener::preSubmit method has been deprecated and will be removed in Symfony 4.0.

Passing objects as URI attributes to the ESI and SSI renderers has been deprecated and will be removed in Symfony 4.0. The inline fragment renderer should be used with object attributes.

Passing a Doctrine Cache instance to the ClassMetadataFactory has been deprecated and will not be supported in Symfony 4.0. You should use the CacheClassMetadataFactory class instead.

Deprecated usage of % at the beginning of an unquoted string.
The Dumper::setIndentation() method is deprecated and will be removed in Symfony 4.0. Pass the indentation level to the constructor instead.
Deprecated support for passing true/false as the second argument to the parse() method to trigger exceptions when an invalid type was passed.

Before:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', true);
```
After:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE);
```

Deprecated support for passing true/false as the third argument to the parse() method to toggle object support.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT);

Deprecated support for passing true/false as the fourth argument to the parse() method to parse objects as maps.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT_FOR_MAP);

Deprecated support for passing true/false as the fourth argument to the dump() method to trigger exceptions when an invalid type was passed.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE);

Deprecated support for passing true/false as the fifth argument to the dump() method to toggle object support.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, Yaml::DUMP_OBJECT);

The !!php/object tag to indicate dumped PHP objects has been deprecated and will be removed in Symfony 4.0. Use the !php/object tag instead.

The DateTimeValidator::PATTERN constant is deprecated and will be removed in Symfony 4.0.