Issue #3014694: Avoid duplicate entry for mass adding terms

Example test data on an empty vocabulary:

animals
-feline
--cat
--lion
cat
-cat3
--cat4
--cat5
dog
-dog
--dog1
--dog2

Closes #3014694

src/Form/AddTermsToVocabularyForm.php

@@ -89,6 +89,12 @@ class AddTermsToVocabularyForm extends FormBase {
       '#title' => $this->t('Create the term in the order provided in the list.'),
       '#description' => $this->t('All terms will be added after the last existing term.'),
     ];
+    $form['ignore_duplicates'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Ignore duplicate terms.'),
+      '#description' => $this->t('Terms which already exist will not be recreated. New child terms of the duplicate will be placed under the existing Taxonomy term.'),
+      '#default_value' => TRUE,
+    ];
     $form['add'] = [
       '#type' => 'submit',
       '#value' => $this->t('Add'),
@@ -105,13 +111,15 @@ class AddTermsToVocabularyForm extends FormBase {
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $term_names_too_long = [];
     $term_names = [];
+    $duplicate_terms = [];
 
     $taxonomy_vocabulary = $form_state->getValue('voc');
     $parents = $form_state->getValue('parents');
     $mass_terms = $form_state->getValue('mass_add');
     $keep_order = $form_state->getValue('keep_order');
+    $ignore_duplicates = $form_state->getValue('ignore_duplicates');
 
-    $new_terms = $this->taxonomyManagerHelper->massAddTerms($mass_terms, $taxonomy_vocabulary->id(), $parents, $term_names_too_long, $keep_order);
+    $new_terms = $this->taxonomyManagerHelper->massAddTerms($mass_terms, $taxonomy_vocabulary->id(), $parents, $term_names_too_long, $keep_order, $ignore_duplicates, $duplicate_terms);
     foreach ($new_terms as $term) {
       $term_names[] = $term->label();
     }
@@ -124,6 +132,9 @@ class AddTermsToVocabularyForm extends FormBase {
         '%names' => implode(', ', $term_names_too_long),
       ]));
     }
+    if (!empty($duplicate_terms)) {
+      $this->messenger()->addWarning($this->t('Skipped the creation of duplicate taxonomy term(s): %duplicate_terms', ['%duplicate_terms' => implode(', ', $duplicate_terms)]));
+    }
     $this->messenger()->addMessage($this->t("Terms added: %terms", ['%terms' => implode(', ', $term_names)]));
     $form_state->setRedirect('taxonomy_manager.admin_vocabulary', ['taxonomy_vocabulary' => $taxonomy_vocabulary->id()]);
   }