Memoize custom sources' field layouts

#17484

Author: brandonkelly

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Improved the performance of element indexes when custom sources are defined. ([#17484](https://github.com/craftcms/cms/issues/17484))
 - Fixed a bug where Matrix fields could load nested entries that belonged to other owner elements. ([#17551](https://github.com/craftcms/cms/issues/17551))
 - Fixed a potential user account enumeration bug when `preventUserEnumeration` was enabled.
 

src/services/ElementSources.php

@@ -293,21 +293,21 @@ public function getTableAttributes(string $elementType, string $sourceKey, ?arra
      */
     public function getFieldLayoutsForSource(string $elementType, string $sourceKey): array
     {
-        // Don't bother the element type for custom sources
-        if (str_starts_with($sourceKey, 'custom:')) {
-            $source = $this->_sourceConfig($elementType, $sourceKey);
-            if (empty($source['condition'])) {
-                return Craft::$app->getFields()->getLayoutsByType($elementType);
-            }
-            /** @var ElementConditionInterface $condition */
-            $condition = Craft::$app->getConditions()->createCondition($source['condition']);
-            $query = $elementType::find();
-            $condition->modifyQuery($query);
-            return $query->getFieldLayouts();
-        }
-
         if (!isset($this->_fieldLayouts[$elementType][$sourceKey])) {
-            $this->_fieldLayouts[$elementType][$sourceKey] = $elementType::fieldLayouts($sourceKey);
+            // Don't bother the element type for custom sources
+            if (str_starts_with($sourceKey, 'custom:')) {
+                $source = $this->_sourceConfig($elementType, $sourceKey);
+                if (empty($source['condition'])) {
+                    return Craft::$app->getFields()->getLayoutsByType($elementType);
+                }
+                /** @var ElementConditionInterface $condition */
+                $condition = Craft::$app->getConditions()->createCondition($source['condition']);
+                $query = $elementType::find();
+                $condition->modifyQuery($query);
+                $this->_fieldLayouts[$elementType][$sourceKey] = $query->getFieldLayouts();
+            } else {
+                $this->_fieldLayouts[$elementType][$sourceKey] = $elementType::fieldLayouts($sourceKey);
+            }
         }
 
         return $this->_fieldLayouts[$elementType][$sourceKey];