FIX: Make IsFirst and IsLast work as expected for PaginatedList (fixes …

…#11465)

src/View/SSViewer_Scope.php

@@ -10,6 +10,7 @@
 use SilverStripe\ORM\FieldType\DBFloat;
 use SilverStripe\ORM\FieldType\DBInt;
 use SilverStripe\ORM\FieldType\DBField;
+use SilverStripe\ORM\PaginatedList;
 
 /**
  * This tracks the current scope for an SSViewer instance. It has three goals:
@@ -305,8 +306,8 @@ public function next()
         }
 
         if (!$this->itemIterator) {
-            // Note: it is important that getIterator() is called before count() as implemenations may rely on
-            // this to efficiency get both the number of records and an iterator (e.g. DataList does this)
+            // Note: it is important that getIterator() is called before count() as implementations may rely on
+            // this to efficiently get both the number of records and an iterator (e.g. DataList does this)
 
             // Item may be an array or a regular IteratorAggregate
             if (is_array($this->item)) {
@@ -319,11 +320,19 @@ public function next()
                 $this->itemIterator->rewind();
             }
 
-            // If the item implements Countable, use that to fetch the count, otherwise we have to inspect the
-            // iterator and then rewind it.
-            if ($this->item instanceof Countable) {
+            // Special case: we *don't* want to use count() on PaginatedList. This is because it'll call
+            // PaginatedList::count(), which currently returns the full list count rather than the count of items
+            // on the current page (which is what we need for the iterator count)
+            if ($this->item instanceof PaginatedList) {
+                // We have to re-fetch the iterator before calling getInnerIterator(): we need to count a copy of the
+                // inner iterator because it's a generator so can't be rewound or cloned
+                $innerIterator = $this->item->getIterator()->getInnerIterator();
+                $this->itemIteratorTotal = iterator_count($innerIterator);
+            } elseif ($this->item instanceof Countable) {
+                // If the item implements Countable, use that to fetch the count
                 $this->itemIteratorTotal = count($this->item);
             } else {
+                // Otherwise we have to inspect the iterator and then rewind it
                 $this->itemIteratorTotal = iterator_count($this->itemIterator);
                 $this->itemIterator->rewind();
             }

tests/php/View/SSViewerTest.php

@@ -1480,6 +1480,37 @@ public function testSSViewerBasicIteratorSupport()
         $this->assertEquals("", $result, "Only numbers that are multiples of 11 are returned. I.e. nothing returned");
     }
 
+    public function testSSViewerBasicIteratorSupportWithPaginatedList()
+    {
+        $list = new ArrayList([
+            ['Val' => 1],
+            ['Val' => 2],
+            ['Val' => 3],
+            ['Val' => 4],
+            ['Val' => 5],
+            ['Val' => 6],
+        ]);
+        $paginatedList = new PaginatedList($list);
+        $paginatedList->setPageLength(2);
+        $data = new ArrayData([
+            'PaginatedList' => $paginatedList
+        ]);
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsFirst %>$Val<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("1", $result, "Only the first item on the first page is rendered");
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsLast %>$Val<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("2", $result, "Only the last item on the first page is rendered");
+
+        $paginatedList->setCurrentPage(2);
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsFirst %>$Val<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("3", $result, "Only the first item on the second page is rendered");
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsLast %>$Val<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("4", $result, "Only the last item on the second page is rendered");
+    }
+
     /**
      * Test $Up works when the scope $Up refers to was entered with a "with" block
      */