Enable donut for C3 - based on issue 2881161.

modules/charts_c3/charts_c3.module

@@ -5,13 +5,26 @@
  * Charts module integration with C3 library.
  */
 
+use Drupal\charts\Theme\ChartsInterface;
+
 /**
  * Implements hook_charts_info().
  */
 function charts_c3_charts_info() {
   $info['c3'] = [
     'label' => t('C3 Charts'),
-    'types' => ['area', 'bar', 'column', 'line', 'pie', 'scatter'],
+    'types' => ['area', 'bar', 'column', 'line', 'pie', 'donut', 'scatter'],
   ];
   return $info;
 }
+
+/**
+ * Implements hook_charts_type_info().
+*/
+function charts_c3_charts_type_info() {
+  $chart_types['donut'] = [
+      'label' => t('Donut'),
+      'axis' => ChartsInterface::CHARTS_SINGLE_AXIS,
+    ];
+  return $chart_types;
+}

modules/charts_c3/src/Charts/C3ChartsRender.php

@@ -82,7 +82,7 @@ class C3ChartsRender implements ChartsRenderInterface {
       array_push($c3Data, $categories);
       $chartData->setColumns($c3Data);
     }
-    else if ($options['type'] == 'pie') {
+    else if ($options['type'] == 'pie' || $options['type'] == 'donut') {
       $chartData->setColumns($c3Data);
     }
     else {
@@ -92,7 +92,7 @@ class C3ChartsRender implements ChartsRenderInterface {
     }
     $chartData->types = $types;
 
-    if ($options['type'] != 'pie') {
+    if ($options['type'] != 'pie' && $options['type'] != 'donut') {
       $c3->setAxis($chartAxis);
     }
 

modules/charts_c3/src/Settings/CThree/ChartData.php

@@ -70,7 +70,7 @@ class ChartData implements \JsonSerializable {
   public function jsonSerialize() {
     $vars = get_object_vars($this);
 
-    if ($vars['type'] == 'pie') {
+    if ($vars['type'] == 'pie' || $vars['type'] == 'donut') {
       unset($vars['x']);
     }