[Translator] Dump native plural formats to po files

src/Symfony/Component/Translation/Dumper/PoFileDumper.php

@@ -51,13 +51,66 @@ public function formatCatalogue(MessageCatalogue $messages, $domain, array $opti
                 $output .= $this->formatComments(implode(' ', (array) $metadata['sources']), ':');
             }
 
-            $output .= sprintf('msgid "%s"'."\n", $this->escape($source));
-            $output .= sprintf('msgstr "%s"'."\n", $this->escape($target));
+            $sourceRules = $this->getStandardRules($source);
+            $targetRules = $this->getStandardRules($target);
+            if (2 == \count($sourceRules) && $targetRules !== []) {
+                $output .= sprintf('msgid "%s"'."\n", $this->escape($sourceRules[0]));
+                $output .= sprintf('msgid_plural "%s"'."\n", $this->escape($sourceRules[1]));
+                foreach ($targetRules as $i => $targetRule) {
+                    $output .= sprintf('msgstr[%d] "%s"'."\n", $i, $this->escape($targetRule));
+                }
+            } else {
+                $output .= sprintf('msgid "%s"'."\n", $this->escape($source));
+                $output .= sprintf('msgstr "%s"'."\n", $this->escape($target));
+            }
         }
 
         return $output;
     }
 
+    private function getStandardRules(string $id)
+    {
+        // Partly copied from TranslatorTrait::trans.
+        $parts = [];
+        if (preg_match('/^\|++$/', $id)) {
+            $parts = explode('|', $id);
+        } elseif (preg_match_all('/(?:\|\||[^\|])++/', $id, $matches)) {
+            $parts = $matches[0];
+        }
+
+        $intervalRegexp = <<<'EOF'
+/^(?P<interval>
+    ({\s*
+        (\-?\d+(\.\d+)?[\s*,\s*\-?\d+(\.\d+)?]*)
+    \s*})
+
+        |
+
+    (?P<left_delimiter>[\[\]])
+        \s*
+        (?P<left>-Inf|\-?\d+(\.\d+)?)
+        \s*,\s*
+        (?P<right>\+?Inf|\-?\d+(\.\d+)?)
+        \s*
+    (?P<right_delimiter>[\[\]])
+)\s*(?P<message>.*?)$/xs
+EOF;
+
+        $standardRules = [];
+        foreach ($parts as $part) {
+            $part = trim(str_replace('||', '|', $part));
+
+            if (preg_match($intervalRegexp, $part)) {
+                // Explicit rule is not a standard rule.
+                return [];
+            } else {
+                $standardRules[] = $part;
+            }
+        }
+
+        return $standardRules;
+    }
+
     /**
      * {@inheritdoc}
      */

src/Symfony/Component/Translation/Tests/Dumper/PoFileDumperTest.php

@@ -45,4 +45,17 @@ public function testFormatCatalogue()
 
         $this->assertStringEqualsFile(__DIR__.'/../fixtures/resources.po', $dumper->formatCatalogue($catalogue, 'messages'));
     }
+
+    public function testDumpPlurals()
+    {
+        $catalogue = new MessageCatalogue('en');
+        $catalogue->add([
+            'foo|foos' => 'bar|bars',
+            '{0} no foos|one foo|%count% foos' => '{0} no bars|one bar|%count% bars',
+        ]);
+
+        $dumper = new PoFileDumper();
+
+        $this->assertStringEqualsFile(__DIR__.'/../fixtures/plurals.po', $dumper->formatCatalogue($catalogue, 'messages'));
+    }
 }

src/Symfony/Component/Translation/Tests/Loader/PoFileLoaderTest.php

@@ -34,7 +34,11 @@ public function testLoadPlurals()
         $resource = __DIR__.'/../fixtures/plurals.po';
         $catalogue = $loader->load($resource, 'en', 'domain1');
 
-        $this->assertEquals(['foo' => 'bar', 'foos' => 'bar|bars'], $catalogue->all('domain1'));
+        $this->assertEquals([
+            'foo' => 'bar',
+            'foos' => 'bar|bars',
+            '{0} no foos|one foo|%count% foos' => '{0} no bars|one bar|%count% bars',
+        ], $catalogue->all('domain1'));
         $this->assertEquals('en', $catalogue->getLocale());
         $this->assertEquals([new FileResource($resource)], $catalogue->getResources());
     }

src/Symfony/Component/Translation/Tests/fixtures/plurals.po

@@ -1,5 +1,13 @@
+msgid ""
+msgstr ""
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Language: en\n"
+
 msgid "foo"
 msgid_plural "foos"
 msgstr[0] "bar"
 msgstr[1] "bars"
 
+msgid "{0} no foos|one foo|%count% foos"
+msgstr "{0} no bars|one bar|%count% bars"