New in Symfony 2.8: YAML deprecations

Deprecated non-escaped \ in double-quoted strings

This deprecation is common when defining the classes of the services:

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app.user_manager:
    class: "AppBundle\Manager\UserManager"
    # ...

The alternative is either remove the double quotes or escape the \ backslash doubling it:

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app.user_manager:
    # remove double quotes...
    class: AppBundle\Manager\UserManager
    # ...or escape backslashes
    class: "AppBundle\\Manager\\UserManager"
    # ...

Deprecated usage of @ at the beginning of unquoted strings

This deprecation has a big impact because lots of services use the @service_id notation to define their dependencies:

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app.user_manager:
    # ...
    arguments: [@router, @logger, @doctrine.orm.entity_manager]

According to Yaml specification, unquoted strings cannot start with @, so you must wrap these arguments with single or double quotes:

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app.user_manager:
    # ...
    arguments: ['@router', '@logger', '@doctrine.orm.entity_manager']

Deprecated usage of reserved characters at the beginning of unquoted strings

These deprecations should have a low impact for Symfony developers because it's uncommon to use these characters as the beginning of unquoted strings:

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app.user_manager:
    # ...
    arguments: [`string`, |string, >string]

The solution is to wrap these strings with single or double quotes:

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app.user_manager:
    # ...
    arguments: ['`string`', '|string', '>string']

Deprecations are always a pain for developers and we try to avoid them as much as possible. But allowing to create Yaml files which don't respect the official specification is unquestionably wrong. The recent Symfony 3.0 release was the perfect moment to fix these problems.