feature #28952 [Translation] allow using the ICU message format using domains with the "+intl-icu" suffix (nicolas-grekas)

This PR was merged into the 4.2-dev branch.

Discussion
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[Translation] allow using the ICU message format using domains with the "+intl-icu" suffix

| Q             | A
| ------------- | ---
| Branch?       | 4.2
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no (unless merged after 4.2)
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This PR replaces the `FallbackFormatter` logic by explicit opt-in.
This allows triggering accurate exceptions when one wants to use the ICU message format but the extension (or the polyfill) is missing.
The way to opt-in is to put messages in a domain with the `+intl-icu` suffix *at loading/declaration time*.
E.g. translations in `messages+intl-icu.en.yaml` will be read as part of the `messages` domain , but will be parsed by intl's `MessageFormatter` instead of the default Symfony one.
To make it seamless to adopt the ICU format, `%`s are trimmed from parameter keys (idea borrowed from https://github.com/webfactory/WebfactoryIcuTranslationBundle)

This is for 4.2 as it changes a feature that is not released yet.
ping @Nyholm - we drafted this together.

Commits
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d95cc4d4c6 [Translation] allow using the ICU message format using domains with the "+intl-icu" suffix

Author: fabpot

DependencyInjection/Configuration.php

@@ -699,7 +699,7 @@ private function addTranslatorSection(ArrayNodeDefinition $rootNode)
                             ->defaultValue(array('en'))
                         ->end()
                         ->booleanNode('logging')->defaultValue(false)->end()
-                        ->scalarNode('formatter')->defaultValue(class_exists(\MessageFormatter::class) ? 'translator.formatter.default' : 'translator.formatter.symfony')->end()
+                        ->scalarNode('formatter')->defaultValue('translator.formatter.default')->end()
                         ->scalarNode('default_path')
                             ->info('The default path used to load translations')
                             ->defaultValue('%kernel.project_dir%/translations')

Resources/config/translation.xml

@@ -29,15 +29,9 @@
             <tag name="monolog.logger" channel="translation" />
         </service>
 
-        <service id="translator.formatter.symfony" class="Symfony\Component\Translation\Formatter\MessageFormatter">
+        <service id="translator.formatter.default" class="Symfony\Component\Translation\Formatter\MessageFormatter">
             <argument type="service" id="identity_translator" />
         </service>
-        <service id="translator.formatter.intl" class="Symfony\Component\Translation\Formatter\IntlMessageFormatter" public="false" />
-        <service id="translator.formatter.fallback" class="Symfony\Component\Translation\Formatter\FallbackFormatter" public="false">
-            <argument type="service" id="translator.formatter.intl" />
-            <argument type="service" id="translator.formatter.symfony" />
-        </service>
-        <service id="translator.formatter.default" alias="translator.formatter.fallback" />
 
         <service id="translation.loader.php" class="Symfony\Component\Translation\Loader\PhpFileLoader">
             <tag name="translation.loader" alias="php" />

Tests/DependencyInjection/ConfigurationTest.php

@@ -189,7 +189,7 @@ protected static function getBundleDefaultConfig()
                 'enabled' => !class_exists(FullStack::class),
                 'fallbacks' => array('en'),
                 'logging' => false,
-                'formatter' => \class_exists('MessageFormatter') ? 'translator.formatter.default' : 'translator.formatter.symfony',
+                'formatter' => 'translator.formatter.default',
                 'paths' => array(),
                 'default_path' => '%kernel.project_dir%/translations',
             ),