Issue #1884762 by tim.plunkett, Gábor Hojtsy: Block forms should use #type => machine_name().

core/modules/block/lib/Drupal/block/BlockBase.php

@@ -241,11 +241,15 @@ public function form($form, &$form_state) {
       '#default_value' => !$entity->isNew() ? $entity->label() : $definition['subject'],
     );
     $form['machine_name'] = array(
-      '#type' => 'textfield',
+      '#type' => 'machine_name',
       '#title' => t('Block machine name'),
       '#maxlength' => 64,
       '#description' => t('A unique name to save this block configuration. Must be alpha-numeric and be underscore separated.'),
       '#default_value' => $entity->id(),
+      '#machine_name' => array(
+        'exists' => 'block_load',
+        'replace_pattern' => '[^a-z0-9_.]+',
+      ),
       '#required' => TRUE,
       '#disabled' => !$entity->isNew(),
     );
@@ -419,12 +423,7 @@ public function blockForm($form, &$form_state) {
    * @see \Drupal\block\BlockBase::blockValidate()
    */
   public function validate($form, &$form_state) {
-    if (empty($form['machine_name']['#disabled'])) {
-      if (preg_match('/[^a-zA-Z0-9_]/', $form_state['values']['machine_name'])) {
-        form_set_error('machine_name', t('Block name must be alphanumeric or underscores only.'));
-      }
-    }
-    else {
+    if (!empty($form['machine_name']['#disabled'])) {
       $config_id = explode('.', $form_state['values']['machine_name']);
       $form_state['values']['machine_name'] = array_pop($config_id);
     }

core/modules/block/lib/Drupal/block/Tests/BlockLanguageTest.php

@@ -62,7 +62,7 @@ public function testLanguageBlockVisibility() {
     // Enable a standard block and set the visibility setting for one language.
     $edit = array(
       'visibility[language][langcodes][en]' => TRUE,
-      'machine_name' => $this->randomName(8),
+      'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
     );
     $this->drupalPost('admin/structure/block/add/system_powered_by_block' . '/' . $default_theme, $edit, t('Save block'));

core/modules/block/lib/Drupal/block/Tests/BlockTest.php

@@ -157,7 +157,7 @@ public function testCustomBlockFormat() {
     $this->removeDefaultBlocks();
 
     // Add a new custom block by filling out the input form on the admin/structure/block/add page.
-    $info = $this->randomName(8);
+    $info = strtolower($this->randomName(8));
     $custom_block['machine_name'] = $info;
     $custom_block['info'] = $info;
     $custom_block['label'] = $this->randomName(8);
@@ -199,7 +199,7 @@ function testBlockVisibility() {
     // Enable a standard block.
     $default_theme = variable_get('theme_default', 'stark');
     $edit = array(
-      'machine_name' => $this->randomName(8),
+      'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
       'label' => $title,
     );
@@ -239,7 +239,7 @@ function testBlockVisibilityListedEmpty() {
     // Enable a standard block.
     $default_theme = variable_get('theme_default', 'stark');
     $edit = array(
-      'machine_name' => $this->randomName(8),
+      'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
       'label' => $title,
       'visibility[path][visibility]' => BLOCK_VISIBILITY_LISTED,
@@ -270,7 +270,7 @@ function testBlock() {
     $block = array();
     $block['id'] = 'system_powered_by_block';
     $block['label'] = $this->randomName(8);
-    $block['machine_name'] = $this->randomName(8);
+    $block['machine_name'] = strtolower($this->randomName(8));
     $block['theme'] = variable_get('theme_default', 'stark');
     $block['region'] = 'header';
 
@@ -351,7 +351,7 @@ function testBlockRehash() {
     // Add a test block.
     $block = array();
     $block['id'] = 'test_cache';
-    $block['machine_name'] = $this->randomName(8);
+    $block['machine_name'] = strtolower($this->randomName(8));
     $block['theme'] = variable_get('theme_default', 'stark');
     $block['region'] = 'header';
     $block = $this->drupalPlaceBlock('test_cache', array('region' => 'header'));
@@ -427,7 +427,7 @@ function testBlockModuleDisable() {
     // that the form still functions as expected.
     $edit = array(
       'label' => $this->randomName(8),
-      'machine_name' => $this->randomName(8),
+      'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
     );
     $this->drupalPost('admin/structure/block/add/system_powered_by_block/stark', $edit, t('Save block'));