[Form] Keep preferred_choices order for choice groups

Author: vilius-g

ChoiceList/Factory/DefaultChoiceListFactory.php

@@ -101,6 +101,14 @@ public function createView(ChoiceListInterface $list, $preferredChoices = null,
                     unset($otherViews[$key]);
                 }
             }
+
+            foreach ($preferredViewsOrder as $key => $groupViewsOrder) {
+                if ($groupViewsOrder) {
+                    $preferredViewsOrder[$key] = min($groupViewsOrder);
+                } else {
+                    unset($preferredViewsOrder[$key]);
+                }
+            }
         } else {
             // Otherwise use the original structure of the choices
             self::addChoiceViewsFromStructuredValues(
@@ -245,6 +253,9 @@ private static function addChoiceViewsGroupedByCallable($groupBy, $choice, $valu
                 $preferredViews[$groupLabel] = new ChoiceGroupView($groupLabel);
                 $otherViews[$groupLabel] = new ChoiceGroupView($groupLabel);
             }
+            if (!isset($preferredViewsOrder[$groupLabel])) {
+                $preferredViewsOrder[$groupLabel] = [];
+            }
 
             self::addChoiceView(
                 $choice,
@@ -255,7 +266,7 @@ private static function addChoiceViewsGroupedByCallable($groupBy, $choice, $valu
                 $attr,
                 $isPreferred,
                 $preferredViews[$groupLabel]->choices,
-                $preferredViewsOrder,
+                $preferredViewsOrder[$groupLabel],
                 $otherViews[$groupLabel]->choices
             );
         }

Tests/ChoiceList/Factory/DefaultChoiceListFactoryTest.php

@@ -256,6 +256,37 @@ public function testCreateViewFlatPreferredChoicesSameOrder()
         );
     }
 
+    public function testCreateViewFlatPreferredChoiceGroupsSameOrder()
+    {
+        $view = $this->factory->createView(
+            $this->list,
+            [$this->obj4, $this->obj2, $this->obj1, $this->obj3],
+            null, // label
+            null, // index
+            [$this, 'getGroup']
+        );
+
+        $preferredLabels = array_map(static function (ChoiceGroupView $groupView): array {
+            return array_map(static function (ChoiceView $view): string {
+                return $view->label;
+            }, $groupView->choices);
+        }, $view->preferredChoices);
+
+        $this->assertEquals(
+            [
+                'Group 2' => [
+                    2 => 'C',
+                    3 => 'D',
+                ],
+                'Group 1' => [
+                    0 => 'A',
+                    1 => 'B',
+                ],
+            ],
+            $preferredLabels
+        );
+    }
+
     public function testCreateViewFlatPreferredChoicesEmptyArray()
     {
         $view = $this->factory->createView(