API Add getSourceList() method to searchable dropdowns

This can be useful for checking the current class the dropdown holds,
similar to `getSourceObject()` on a tree dropdown

Author: GuySartorelli

src/Forms/SearchableDropdownTrait.php

@@ -182,8 +182,8 @@ public function getSearchContext(): ?SearchContext
         if ($this->searchContext) {
             return $this->searchContext;
         }
-        if ($this->sourceList) {
-            $dataClass = $this->sourceList->dataClass();
+        if ($this->getSourceList()) {
+            $dataClass = $this->getSourceList()->dataClass();
             /** @var DataObject $obj */
             $obj = $dataClass::create();
             return $obj->getDefaultSearchContext();
@@ -265,7 +265,7 @@ public function setIsSearchable(bool $isSearchable): static
      */
     public function getSource(): array
     {
-        return $this->getListMap($this->sourceList);
+        return $this->getListMap($this->getSourceList());
     }
 
     public function Field($properties = [])
@@ -286,6 +286,15 @@ public function setSource($source): static
         return $this;
     }
 
+    /**
+     * Get the underlying list that represents the source for this dropdown.
+     * To set, use setSource().
+     */
+    public function getSourceList(): ?DataList
+    {
+        return $this->sourceList;
+    }
+
     /**
      * Get the field to use for the label of the option
      * This field is also used for searching if that field exists in the database and search context is not being used
@@ -499,10 +508,10 @@ private function getDefaultSchemaValue()
 
     private function getOptionsForSearchRequest(string $term): array
     {
-        if (!$this->sourceList) {
+        if (!$this->getSourceList()) {
             return [];
         }
-        $dataClass = $this->sourceList->dataClass();
+        $dataClass = $this->getSourceList()->dataClass();
         $labelField = $this->getLabelField();
         /** @var DataObject $obj */
         $obj = $dataClass::create();
@@ -530,14 +539,14 @@ private function getOptionsForSearchRequest(string $term): array
     private function getOptionsForSchema(bool $onlySelected = false): ArrayList
     {
         $options = ArrayList::create();
-        if (!$this->sourceList) {
+        if (!$this->getSourceList()) {
             return $options;
         }
         $values = $this->getValueArray();
         if (empty($values)) {
             $selectedValuesList = ArrayList::create();
         } else {
-            $selectedValuesList = $this->sourceList->filterAny(['ID' => $values]);
+            $selectedValuesList = $this->getSourceList()->filterAny(['ID' => $values]);
         }
         // SearchableDropdownField will have the getHasEmptyDefault() method from SingleSelectField
         // Note that SingleSelectField::getSourceEmpty() will not be called for the react-select component
@@ -552,7 +561,7 @@ private function getOptionsForSchema(bool $onlySelected = false): ArrayList
         if ($onlySelected) {
             $options = $this->updateOptionsForSchema($options, $selectedValuesList, $selectedValuesList);
         } else {
-            $options = $this->updateOptionsForSchema($options, $this->sourceList, $selectedValuesList);
+            $options = $this->updateOptionsForSchema($options, $this->getSourceList(), $selectedValuesList);
         }
         return $options;
     }
@@ -609,14 +618,14 @@ public function performReadonlyTransformation()
         // call to $this->getSource() which will load the entire DataList into memory which
         // causes issues with very large datasets and isn't needed when the field is read-only
         $field = call_user_func('SilverStripe\\Forms\\FormField::castedCopy', SearchableLookupField::class);
-        $field->setSource($this->sourceList);
+        $field->setSource($this->getSourceList());
         $field->setReadonly(true);
 
         return $field;
     }
 
     protected function getSourceValues()
     {
-        return $this->sourceList->sort(null)->column('ID');
+        return $this->getSourceList()->sort(null)->column('ID');
     }
 }