Fix extracting POT files from vendor prefix plugins.

Correctly generate the output file name for vendor prefixed plugins.
As per the convention defined in MessagesFileLoader, prefixed plugins
only use the plugin name as the domain.po/pot file.

Refs #8316

src/Shell/Task/ExtractTask.php

@@ -547,7 +547,13 @@ class ExtractTask extends Shell
                 $output .= $header . $sentence;
             }
 
-            $filename = $domain . '.pot';
+            // Remove vendor prefix if present.
+            $slashPosition = strpos($domain, '/');
+            if ($slashPosition !== false) {
+                $domain = substr($domain, $slashPosition + 1);
+            }
+
+            $filename = str_replace('/', '_', $domain) . '.pot';
             $File = new File($this->_output . $filename);
             $response = '';
             while ($overwriteAll === false && $File->exists() && strtoupper($response) !== 'Y') {

tests/TestCase/Shell/Task/ExtractTaskTest.php

@@ -263,7 +263,7 @@ class ExtractTaskTest extends TestCase
     }
 
     /**
-     * Test that is possible to extract messages form a single plugin
+     * Test that is possible to extract messages from a single plugin
      *
      * @return void
      */
@@ -288,6 +288,31 @@ class ExtractTaskTest extends TestCase
     }
 
     /**
+     * Test that is possible to extract messages from a vendored plugin.
+     *
+     * @return void
+     */
+    public function testExtractVendoredPlugin()
+    {
+        Configure::write('App.namespace', 'TestApp');
+
+        $this->Task = $this->getMock(
+            'Cake\Shell\Task\ExtractTask',
+            ['_isExtractingApp', 'in', 'out', 'err', 'clear', '_stop'],
+            [$this->io]
+        );
+
+        $this->Task->params['output'] = $this->path . DS;
+        $this->Task->params['plugin'] = 'Company/TestPluginThree';
+
+        $this->Task->main();
+        $result = file_get_contents($this->path . DS . 'test_plugin_three.pot');
+        $this->assertNotRegExp('#Pages#', $result);
+        $this->assertRegExp('/default\.ctp:\d+/', $result);
+        $this->assertContains('A vendor message', $result);
+    }
+
+    /**
      *  Test that the extract shell overwrites existing files with the overwrite parameter
      *
      * @return void

tests/test_app/Plugin/Company/TestPluginThree/src/Template/Layout/default.ctp

@@ -1,2 +1,3 @@
 default test_three_theme layout
 <?= $this->fetch('content') ?>
+<?= __d('company/test_plugin_three', 'A vendor message') ?>