From d2a51471e9fc0de56bda6ed1656624a3463d7934 Mon Sep 17 00:00:00 2001
From: Maxime Rainville <maxime@silverstripe.com>
Date: Fri, 5 Oct 2018 16:57:37 +1300
Subject: [PATCH] Don't lazy load tab that are not in a TabSet.

---
 src/Forms/GridField/GridFieldLazyLoader.php | 41 ++++++++++++++++++---
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/Forms/GridField/GridFieldLazyLoader.php b/src/Forms/GridField/GridFieldLazyLoader.php
index 8ca6ca1b5..98fe89c53 100755
--- a/src/Forms/GridField/GridFieldLazyLoader.php
+++ b/src/Forms/GridField/GridFieldLazyLoader.php
@@ -2,7 +2,10 @@
 
 namespace SilverStripe\Forms\GridField;
 
+use SilverStripe\Forms\FormField;
+use SilverStripe\Forms\TabSet;
 use SilverStripe\ORM\ArrayList;
+use SilverStripe\ORM\Limitable;
 use SilverStripe\ORM\SS_List;
 
 /**
@@ -19,9 +22,17 @@ class GridFieldLazyLoader implements GridField_DataManipulator, GridField_HTMLPr
      */
     public function getManipulatedData(GridField $gridField, SS_List $dataList)
     {
-        return $this->isLazy($gridField) ?
-            ArrayList::create([]) :
-            $dataList;
+        // If we are lazy loading, empty the list
+        if ($this->isLazy($gridField)) {
+            if ($dataList instanceof Limitable) {
+                // If our original list can be limited, set the limit to 0.
+                $dataList = $dataList->limit(0);
+            } else {
+                // If not, create an empty list instead.
+                $dataList = ArrayList::create([]);
+            }
+        }
+        return $dataList;
     }
 
     /**
@@ -36,12 +47,32 @@ class GridFieldLazyLoader implements GridField_DataManipulator, GridField_HTMLPr
     }
 
     /**
-     * Detect if the current request should include results
+     * Detect if the current request should include results.
      * @param GridField $gridField
      * @return bool
      */
     private function isLazy(GridField $gridField)
     {
-        return $gridField->getRequest()->getHeader('X-Pjax') !== 'CurrentField';
+        return
+            $gridField->getRequest()->getHeader('X-Pjax') !== 'CurrentField' &&
+            $this->isInTabSet($gridField);
+    }
+
+    /**
+     * Recursively check if $field is inside a TabSet.
+     * @param FormField $field
+     * @return bool
+     */
+    private function isInTabSet(FormField $field)
+    {
+        $list = $field->getContainerFieldList();
+        if ($list && $containerField = $list->getContainerField()) {
+            // Classes that extends TabSet might not have the expected JS to lazy load.
+            return get_class($containerField) === TabSet::class
+                ?: $this->isInTabSet($containerField);
+        } else {
+            return false;
+        }
+
     }
 }