[5.2] Allow nested Subform inside a Subform Custom Field

administrator/components/com_fields/forms/field.xml

@@ -81,7 +81,6 @@
 			label="COM_FIELDS_FIELD_ONLY_USE_IN_SUBFORM_LABEL"
 			layout="joomla.form.field.radio.switcher"
 			default="0"
-			showon="type!:subform"
 			>
 			<option value="0">JNO</option>
 			<option value="1">JYES</option>

administrator/components/com_fields/src/Field/SubfieldsField.php

@@ -75,11 +75,6 @@ protected function getOptions()
 
         // Iterate over the custom fields for this context
         foreach (static::$customFieldsCache[$this->context] as $customField) {
-            // Skip our own subform type. We won't have subform in subform.
-            if ($customField->type == 'subform') {
-                continue;
-            }
-
             $options[] = HTMLHelper::_(
                 'select.option',
                 $customField->id,

administrator/components/com_fields/src/Model/FieldModel.php

@@ -580,17 +580,9 @@ public function getForm($data = [], $loadData = true)
             $form->setFieldAttribute('created_user_id', 'filter', 'unset');
         }
 
-        // In case we are editing a field, field type cannot be changed, so some extra handling below is needed
+        // In case we are editing a field, field type cannot be changed, so remove showon attribute to avoid js errors
         if ($fieldId) {
-            $fieldType = $form->getField('type');
-
-            if ($fieldType->value == 'subform') {
-                // Only Use In subform should not be available for subform field type, so we remove it
-                $form->removeField('only_use_in_subform');
-            } else {
-                // Field type could not be changed, so remove showon attribute to avoid js errors
-                $form->setFieldAttribute('only_use_in_subform', 'showon', '');
-            }
+            $form->setFieldAttribute('only_use_in_subform', 'showon', '');
         }
 
         return $form;