feature #28070 [Translator] Use ICU parent locales as fallback locales (thewilkybarkid)

This PR was squashed before being merged into the 4.2-dev branch (closes #28070).

Discussion
----------

[Translator] Use ICU parent locales as fallback locales

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12319
| License       | MIT
| Doc PR        | symfony/symfony-docs#10122

Currently the `Translator` fall backs based on the locale separator (eg `es_AR` to `es`), but the ICU data contains parent locales (eg `es_AR` is a child of `es_419`, as is `es_BO`, `es_EC` etc).

This makes use of the ICU data to add add in these fallbacks. This means the specific locales can be used, but the translations can stored in these groupings (eg `es_419` for Latin American Spanish), as well as adding other sensible fallbacks (eg Cape Verdean Portuguese to `pt_PT`).

Commits
-------

e0f402fc29 [Translator] Use ICU parent locales as fallback locales

Author: fabpot

Data/Generator/LocaleDataGenerator.php

@@ -57,6 +57,7 @@ public function generateData(GeneratorConfig $config)
 
         $locales = $localeScanner->scanLocales($config->getSourceDir().'/locales');
         $aliases = $localeScanner->scanAliases($config->getSourceDir().'/locales');
+        $parents = $localeScanner->scanParents($config->getSourceDir().'/locales');
 
         // Flip to facilitate lookup
         $flippedLocales = array_flip($locales);
@@ -134,6 +135,12 @@ public function generateData(GeneratorConfig $config)
                 'Aliases' => $aliases,
             ));
         }
+
+        // Write parents locale file for the Translation component
+        \file_put_contents(
+            __DIR__.'/../../../Translation/Resources/data/parents.json',
+            \json_encode($parents, \JSON_PRETTY_PRINT).\PHP_EOL
+        );
     }
 
     private function generateLocaleName($locale, $displayLocale)

Data/Util/LocaleScanner.php

@@ -82,4 +82,24 @@ public function scanAliases($sourceDir)
 
         return $aliases;
     }
+
+    /**
+     * Returns all locale parents found in the given directory.
+     */
+    public function scanParents(string $sourceDir): array
+    {
+        $locales = $this->scanLocales($sourceDir);
+        $fallbacks = array();
+
+        foreach ($locales as $locale) {
+            $content = \file_get_contents($sourceDir.'/'.$locale.'.txt');
+
+            // Aliases contain the text "%%PARENT" followed by the aliased locale
+            if (\preg_match('/%%Parent{"([^"]+)"}/', $content, $matches)) {
+                $fallbacks[$locale] = $matches[1];
+            }
+        }
+
+        return $fallbacks;
+    }
 }

Tests/Data/Util/LocaleScannerTest.php

@@ -42,10 +42,13 @@ protected function setUp()
 
         $this->filesystem->touch($this->directory.'/en.txt');
         $this->filesystem->touch($this->directory.'/en_alias.txt');
+        $this->filesystem->touch($this->directory.'/en_child.txt');
         $this->filesystem->touch($this->directory.'/de.txt');
         $this->filesystem->touch($this->directory.'/de_alias.txt');
+        $this->filesystem->touch($this->directory.'/de_child.txt');
         $this->filesystem->touch($this->directory.'/fr.txt');
         $this->filesystem->touch($this->directory.'/fr_alias.txt');
+        $this->filesystem->touch($this->directory.'/fr_child.txt');
         $this->filesystem->touch($this->directory.'/root.txt');
         $this->filesystem->touch($this->directory.'/supplementalData.txt');
         $this->filesystem->touch($this->directory.'/supplementaldata.txt');
@@ -54,6 +57,9 @@ protected function setUp()
         file_put_contents($this->directory.'/en_alias.txt', 'en_alias{"%%ALIAS"{"en"}}');
         file_put_contents($this->directory.'/de_alias.txt', 'de_alias{"%%ALIAS"{"de"}}');
         file_put_contents($this->directory.'/fr_alias.txt', 'fr_alias{"%%ALIAS"{"fr"}}');
+        file_put_contents($this->directory.'/en_child.txt', 'en_GB{%%Parent{"en"}}');
+        file_put_contents($this->directory.'/de_child.txt', 'en_GB{%%Parent{"de"}}');
+        file_put_contents($this->directory.'/fr_child.txt', 'en_GB{%%Parent{"fr"}}');
     }
 
     protected function tearDown()
@@ -63,7 +69,7 @@ protected function tearDown()
 
     public function testScanLocales()
     {
-        $sortedLocales = array('de', 'de_alias', 'en', 'en_alias', 'fr', 'fr_alias');
+        $sortedLocales = array('de', 'de_alias', 'de_child', 'en', 'en_alias', 'en_child', 'fr', 'fr_alias', 'fr_child');
 
         $this->assertSame($sortedLocales, $this->scanner->scanLocales($this->directory));
     }
@@ -74,4 +80,11 @@ public function testScanAliases()
 
         $this->assertSame($sortedAliases, $this->scanner->scanAliases($this->directory));
     }
+
+    public function testScanParents()
+    {
+        $sortedParents = array('de_child' => 'de', 'en_child' => 'en', 'fr_child' => 'fr');
+
+        $this->assertSame($sortedParents, $this->scanner->scanParents($this->directory));
+    }
 }