Issue #2985716 by maxocub, masipila: Cannot save language negotiation settings after upgrade

core/modules/language/src/Plugin/migrate/process/LanguageDomains.php

@@ -20,7 +20,7 @@ class LanguageDomains extends ArrayBuild {
    * {@inheritdoc}
    */
   public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    if ($row->getSourceProperty('domain_negotiation')) {
+    if ($row->getSourceProperty('domain_negotiation_used')) {
       global $base_url;
 
       foreach ($value as $old_key => $old_value) {

core/modules/language/src/Plugin/migrate/source/Language.php

@@ -66,7 +66,7 @@ public function prepareRow(Row $row) {
       // when the 'language_negotiation' variable is set to '3', and in D7, when
       // the 'locale_language_negotiation_url_part' variable is set to '1'.
       if ($this->variableGet('language_negotiation', 0) == 3 || $this->variableGet('locale_language_negotiation_url_part', 0) == 1) {
-        $row->setSourceProperty('domain_negotiation', TRUE);
+        $row->setSourceProperty('domain_negotiation_used', TRUE);
       }
     }
 

core/modules/language/tests/src/Kernel/Migrate/d7/MigrateLanguageNegotiationSettingsTest.php

@@ -53,6 +53,10 @@ public function testLanguageTypes() {
    * Tests the migration with prefix negotiation.
    */
   public function testLanguageNegotiationWithPrefix() {
+    $this->sourceDatabase->update('languages')
+      ->fields(['domain' => ''])
+      ->execute();
+
     $this->executeMigrations([
       'language',
       'd7_language_negotiation_settings',
@@ -68,6 +72,15 @@ public function testLanguageNegotiationWithPrefix() {
       'is' => 'is',
     ];
     $this->assertSame($expected_prefixes, $config->get('url.prefixes'));
+
+    // If prefix negotiation is used, make sure that no domains are migrated.
+    // Otherwise there will be validation errors when trying to save URL
+    // language detection configuration from the UI.
+    $expected_domains = [
+      'en' => '',
+      'is' => '',
+    ];
+    $this->assertSame($expected_domains, $config->get('url.domains'));
   }
 
   /**