Issue #3166044 by anmolgoyal74, spuky, idebr, quietone, sarvjeetsingh,...

Issue #3166044 by anmolgoyal74, spuky, idebr, quietone, sarvjeetsingh, janmejaig, paulocs, ranjith_kumar_k_u, jungle, benjifisher, alexpott: Allow file extensions containing underscores

core/modules/file/src/Plugin/Field/FieldType/FileItem.php

@@ -166,7 +166,7 @@ public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
       '#type' => 'textfield',
       '#title' => t('Allowed file extensions'),
       '#default_value' => $extensions,
-      '#description' => t('Separate extensions with a space or comma and do not include the leading dot.'),
+      '#description' => $this->t("Separate extensions with a comma or space. Each extension can contain alphanumeric characters, '.', and '_', and should start and end with an alphanumeric character."),
       '#element_validate' => [[static::class, 'validateExtensions']],
       '#weight' => 1,
       '#maxlength' => 256,
@@ -227,8 +227,8 @@ public static function validateExtensions($element, FormStateInterface $form_sta
       $extensions = preg_replace('/([, ]+\.?)/', ' ', trim(strtolower($element['#value'])));
       $extension_array = array_unique(array_filter(explode(' ', $extensions)));
       $extensions = implode(' ', $extension_array);
-      if (!preg_match('/^([a-z0-9]+([.][a-z0-9])* ?)+$/', $extensions)) {
-        $form_state->setError($element, t('The list of allowed extensions is not valid, be sure to exclude leading dots and to separate extensions with a comma or space.'));
+      if (!preg_match('/^([a-z0-9]+([._][a-z0-9])* ?)+$/', $extensions)) {
+        $form_state->setError($element, t("The list of allowed extensions is not valid. Allowed characters are a-z, 0-9, '.', and '_'. The first and last characters cannot be '.' or '_', and these two characters cannot appear next to each other. Separate extensions with a comma or space."));
       }
       else {
         $form_state->setValueForElement($element, $extensions);

core/modules/file/tests/src/Functional/FileFieldWidgetTest.php

@@ -501,6 +501,27 @@ public function testFileExtensionsSetting() {
     $edit = ['settings[file_extensions]' => 'jpg php'];
     $this->submitForm($edit, 'Save settings');
     $this->assertSession()->pageTextContains('Saved ' . $field_name . ' configuration.');
+
+    // Check that a file extension with an underscore can be configured.
+    $edit = [
+      'settings[file_extensions]' => 'x_t x.t xt x_y_t',
+    ];
+    $this->drupalGet("admin/structure/types/manage/$type_name/fields/$field_id");
+    $this->submitForm($edit, 'Save settings');
+    $field = FieldConfig::loadByName('node', $type_name, $field_name);
+    $this->assertEquals('x_t x.t xt x_y_t', $field->getSetting('file_extensions'));
+
+    // Check that a file field with an invalid value in allowed extensions
+    // property throws an error message.
+    $invalid_extensions = ['x_.t', 'x._t', 'xt_', 'x__t', '_xt'];
+    foreach ($invalid_extensions as $value) {
+      $edit = [
+        'settings[file_extensions]' => $value,
+      ];
+      $this->drupalGet("admin/structure/types/manage/$type_name/fields/$field_id");
+      $this->submitForm($edit, 'Save settings');
+      $this->assertSession()->pageTextContains("The list of allowed extensions is not valid. Allowed characters are a-z, 0-9, '.', and '_'. The first and last characters cannot be '.' or '_', and these two characters cannot appear next to each other. Separate extensions with a comma or space.");
+    }
   }
 
   /**