fix: better handling for the date format descriptions

Closes #1244458

date_popup/date_popup.module

@@ -206,7 +206,7 @@ function date_popup_element_info() {
   //   - changeYear => TRUE
   //   - autoPopUp => 'focus'
   //   - closeAtTop => FALSE
-  //   - speed => 'immediate'
+  //   - speed => 'immediate'.
   $type['date_popup'] = array(
     '#input' => TRUE,
     '#tree' => TRUE,
@@ -321,6 +321,12 @@ function date_popup_element_process($element, &$form_state, $form) {
     );
   }
 
+  // Display date element description setting.
+  if (isset($element['#instance'])) {
+    $element['#show_element_description'] = $element['#instance']['settings']['show_element_description'] ?? FALSE;
+  }
+  $element['#show_element_description'] = $element['#show_element_description'] ?? FALSE;
+
   $element['date'] = date_popup_process_date_part($element);
   $element['time'] = date_popup_process_time_part($element);
 
@@ -441,15 +447,11 @@ function date_popup_process_date_part(&$element) {
     '#ajax' => !empty($element['#ajax']) ? $element['#ajax'] : FALSE,
     '#required' => $element['#required'],
   );
-  // Do NOT overwrite the actual input with the default value.
-  // @todo Figure out exactly when this is needed, in many places it is not.
-  $sub_element['#description'] = ' ' . t('E.g., @date', array(
-    '@date' => date_format_date(
-        date_example_date(),
-        'custom',
-        date_popup_date_format($element)
-    ),
-  ));
+
+  // Display date element description as placeholder.
+  if (!empty($element['#show_element_description'])) {
+    $sub_element['#attributes']['placeholder'] = date_format_date(date_example_date(), 'custom', date_popup_date_format($element));
+  }
 
   return $sub_element;
 }
@@ -507,7 +509,7 @@ function date_popup_process_time_part(&$element) {
       $grans = array('hour', 'minute', 'second');
       $time_granularity = array_intersect($granularity, $grans);
       $format = date_popup_format_to_popup_time(date_limit_format($element['#date_format'], $time_granularity), 'wvega');
-      $default_value = isset($element['#default_value']) ? $element['#default_value'] : '';
+      $default_value = $element['#default_value'] ?? '';
       // The first value in the dropdown list should be the same as the element
       // default_value, but it needs to be in JS format (i.e. milliseconds since
       // the epoch).
@@ -551,17 +553,13 @@ function date_popup_process_time_part(&$element) {
     '#required' => $element['#required'],
   );
 
-  // Do NOT overwrite the actual input with the default value.
-  // @todo Figure out exactly when this is needed, in many places it is not.
   $example_date = date_now();
   date_increment_round($example_date, $element['#date_increment']);
-  $sub_element['#description'] = t('E.g., @date', array(
-    '@date' => date_format_date(
-      $example_date,
-      'custom',
-      date_popup_time_format($element)
-    ),
-  ));
+
+  // Display date element description as placeholder.
+  if (!empty($element['#show_element_description'])) {
+    $sub_element['#attributes']['placeholder'] = date_format_date(date_example_date(), 'custom', date_popup_time_format($element));
+  }
 
   return ($sub_element);
 }