Preserve POT file order when updating PO files

features/updatepo.feature

@@ -488,6 +488,10 @@ Feature: Update existing PO files from a POT file
       #: foo-plugin.php:1
       msgid "Some string"
       msgstr ""
+
+      #: foo-plugin.php:2
+      msgid "Some other string"
+      msgstr ""
       """
     And a foo-plugin/foo-plugin-de_DE.po file:
       """
@@ -527,3 +531,55 @@ Feature: Update existing PO files from a POT file
       """
       "PO-Revision-Date: 2018-05-02T22:06:24+00:00\n"
       """
+
+  Scenario: Keeps POT file order of translations
+    Given an empty foo-plugin directory
+    And a foo-plugin/foo-plugin.pot file:
+      """
+      # Copyright (C) 2018 Foo Plugin
+      # This file is distributed under the same license as the Foo Plugin package.
+      msgid ""
+      msgstr ""
+      "Project-Id-Version: Foo Plugin\n"
+      "Content-Type: text/plain; charset=UTF-8\n"
+      "X-Domain: foo-plugin\n"
+
+      #: foo-plugin.php:1
+      msgid "First string"
+      msgstr ""
+
+      #: foo-plugin.php:10
+      msgid "Second string"
+      msgstr ""
+
+      #: foo-plugin.php:20
+      msgid "Third string"
+      msgstr ""
+      """
+    And a foo-plugin/foo-plugin-de_DE.po file:
+      """
+      # Copyright (C) 2018 Foo Plugin
+      # This file is distributed under the same license as the Foo Plugin package.
+      msgid ""
+      msgstr ""
+      "Project-Id-Version: Foo Plugin\n"
+      "Content-Type: text/plain; charset=UTF-8\n"
+      "Language: de_DE\n"
+      "X-Domain: foo-plugin\n"
+
+      #: foo-plugin.php:20
+      msgid "Third string"
+      msgstr "Dritte Zeichenfolge"
+
+      #: foo-plugin.php:1
+      msgid "First string"
+      msgstr "Erste Zeichenfolge"
+      """
+
+    When I run `wp i18n update-po foo-plugin/foo-plugin.pot foo-plugin/foo-plugin-de_DE.po`
+    Then STDOUT should be:
+      """
+      Success: Updated 1 file.
+      """
+    And STDERR should be empty
+    And the contents of the foo-plugin/foo-plugin-de_DE.po file should match /First string.*Second string.*Third string/s

src/UpdatePoCommand.php

@@ -91,7 +91,10 @@ public function __invoke( $args, $assoc_args ) {
 			// Uses gmdate() for consistency across different server timezones.
 			$po_translations->setHeader( 'PO-Revision-Date', gmdate( 'Y-m-d\TH:i:sP' ) );
 
-			if ( ! $po_translations->toPoFile( $file->getPathname() ) ) {
+			// Reorder translations to match POT file order.
+			$ordered_translations = $this->reorder_translations( $po_translations, $pot_translations );
+
+			if ( ! $ordered_translations->toPoFile( $file->getPathname() ) ) {
 				WP_CLI::warning( sprintf( 'Could not update file %s', $file->getPathname() ) );
 				continue;
 			}
@@ -101,4 +104,31 @@ public function __invoke( $args, $assoc_args ) {
 
 		WP_CLI::success( sprintf( 'Updated %d %s.', $result_count, Utils\pluralize( 'file', $result_count ) ) );
 	}
+
+	/**
+	 * Reorder translations to match the POT file order.
+	 *
+	 * @param Translations $po_translations  The merged PO translations.
+	 * @param Translations $pot_translations The POT translations (source of truth for order).
+	 *
+	 * @return Translations Translations object with entries in POT file order.
+	 */
+	private function reorder_translations( Translations $po_translations, Translations $pot_translations ) {
+		$ordered = new Translations();
+
+		// Copy headers from the merged PO translations.
+		foreach ( $po_translations->getHeaders() as $name => $value ) {
+			$ordered->setHeader( $name, $value );
+		}
+
+		// Add translations in POT file order.
+		foreach ( $pot_translations as $pot_entry ) {
+			$po_entry = $po_translations->find( $pot_entry );
+			if ( $po_entry ) {
+				$ordered[] = $po_entry->getClone();
+			}
+		}
+
+		return $ordered;
+	}
 }