[Routing] The parameter "app.route_prefix" must be defined

[mfrieling]

I followed How to Use Service Container Parameters in your Routes to configure the _locale prefix for the Sonata Admin routes in my project and got the error message

The parameter "app.route_prefix" must be defined.

After a second look on the documentation and my local changes I found out that the section "You can also use a parameter to define your route path (or part of your path)" uses the %app.route_prefix% parameter but never defines it. In the documentation the information should be added, where and how to define this parameter, especially that "_locale" must be added as placeholder {_locale} and not as _locale:

YAML:

# config/services.yaml
parameters:
  app.route_prefix: '{_locale}'

XML:

<!-- config/services.xml -->
        <?xml version="1.0" charset="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                https://symfony.com/schema/dic/services/services-1.0.xsd">

            <parameters>
                <parameter key="app.route_prefix">{_locale}</parameter>
            </parameters>
        </container>

PHP:

// config/services.php
        $container->setParameter('app.route_prefix', '{_locale}');

I'm not editing the documentation on my own because I don't know the exact syntax for RST and and the Symfony rules for the documentation and at the moment have no time to read into it :-(

[javiereguiluz]

@mfrieling thanks for reporting this issue. You are right and we're trying to improve this in #11587. However, we prefer to not use the {_locale} parameter as an example. The reason is that "routing + locale/i18n" has improved a lot in recent Symfony versions, so we don't want to mix those here. that's why we used a normal parameter. Thanks.

[mfrieling]

@javiereguiluz I understand your rationale to use a generic parameter. Mine to use {_locale} was to complete the existing example of https://symfony.com/doc/current/routing/service_container_parameters.html using it, because without the missing app.route_prefix parameter that example simply doesn't work. Therefore I suggest fixing that example accordingly as well to giving an example with a generic parameter as you've done in #11587.