Maintain field settings when switching field types

CHANGELOG-WIP.md

@@ -3,6 +3,7 @@
 ### Administration
 - Added the `--batch-size` option for `resave/*` commands. ([#16586](https://github.com/craftcms/cms/issues/16586))
 - Dragging headings within the Customize Sources modal now also drags any subsequent sources. ([#16737](https://github.com/craftcms/cms/issues/16737))
+- When switching field types, any field settings which are defined by the same base class are now preserved. ([#16783](https://github.com/craftcms/cms/pull/16783))
 
 ### Extensibility
 - Global nav items and breadcrumbs can now have `aria-label` attributes via an `ariaLabel` property.

src/controllers/FieldsController.php

@@ -13,11 +13,14 @@
 use craft\fields\MissingField;
 use craft\fields\PlainText;
 use craft\helpers\ArrayHelper;
+use craft\helpers\Component;
 use craft\helpers\UrlHelper;
 use craft\models\FieldGroup;
 use craft\models\FieldLayoutTab;
 use craft\web\assets\fieldsettings\FieldSettingsAsset;
 use craft\web\Controller;
+use ReflectionException;
+use ReflectionProperty;
 use yii\web\BadRequestHttpException;
 use yii\web\NotFoundHttpException;
 use yii\web\Response;
@@ -292,9 +295,32 @@ public function actionRenderSettings(): Response
         $this->requirePostRequest();
         $this->requireAcceptsJson();
 
+        /** @var class-string<FieldInterface> $type */
         $type = $this->request->getRequiredBodyParam('type');
         $field = Craft::$app->getFields()->createField($type);
 
+        /** @var class-string<FieldInterface>|null $oldType */
+        $oldType = $this->request->getBodyParam('oldType');
+        if ($oldType && Component::validateComponentClass($oldType, FieldInterface::class)) {
+            $settingsStr = $this->request->getBodyParam('settings');
+            parse_str($settingsStr, $postedOldSettings);
+            $oldNamespace = $this->request->getBodyParam('oldNamespace');
+            $settings = ArrayHelper::getValue($postedOldSettings, $oldNamespace, []);
+
+            // Remove any settings that aren't defined by the same class between both types
+            $settings = array_filter($settings, function($attribute) use ($type, $oldType) {
+                try {
+                    $r1 = new ReflectionProperty($type, $attribute);
+                    $r2 = new ReflectionProperty($oldType, $attribute);
+                    return $r1->getDeclaringClass()->name === $r2->getDeclaringClass()->name;
+                } catch (ReflectionException) {
+                    return false;
+                }
+            }, ARRAY_FILTER_USE_KEY);
+
+            Craft::configure($field, $settings);
+        }
+
         $view = Craft::$app->getView();
         $html = $view->renderTemplate('settings/fields/_type-settings.twig', [
             'field' => $field,

src/web/assets/fieldsettings/src/fieldsettings.js

@@ -32,10 +32,13 @@
           });
         }
 
+        const oldType = this.currentType;
+        const settings = $('<form/>')
+          .append(this.$container.clone())
+          .serialize();
+
         // Save & detach the current settings
-        this.typeSettings[this.currentType] = this.$container
-          .children()
-          .detach();
+        this.typeSettings[oldType] = this.$container.children().detach();
 
         this.currentType = this.$toggle.val();
 
@@ -54,12 +57,15 @@
 
         let data = {
           type: this.currentType,
+          oldType,
+          settings,
         };
         if (this.namespace) {
           data.namespace = this.namespace.replace(
             /__TYPE__/g,
             this.currentType
           );
+          data.oldNamespace = this.namespace.replace(/__TYPE__/g, oldType);
         }
 
         Craft.sendActionRequest('POST', 'fields/render-settings', {