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

…silverstripe#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

@@ -44,8 +44,11 @@ class SSViewerTest extends SapphireTest
      */
     protected $oldServer = [];
 
+    protected static $fixture_file = 'SSViewerTest/SSViewerTestModel.yml';
+
     protected static $extra_dataobjects = [
         SSViewerTest\TestObject::class,
+        SSViewerTest\SSViewerTestModel::class,
     ];
 
     protected function setUp(): void
@@ -1480,6 +1483,28 @@ public function testSSViewerBasicIteratorSupport()
         $this->assertEquals("", $result, "Only numbers that are multiples of 11 are returned. I.e. nothing returned");
     }
 
+    public function testSSViewerBasicIteratorSupportWithPaginatedList()
+    {
+        $paginatedList = PaginatedList::create(SSViewerTestModel::get())->setPageLength(2);
+        $data = new ArrayData([
+            'PaginatedList' => $paginatedList
+        ]);
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsFirst %>$Name<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("steven", $result, "Only the first name on the first page is rendered");
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsLast %>$Name<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("bonny", $result, "Only the last name on the first page is rendered");
+
+        $paginatedList->setCurrentPage(2);
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsFirst %>$Name<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("sam", $result, "Only the first name on the second page is rendered");
+
+        $result = $this->render('<% loop PaginatedList %><% if $IsLast %>$Name<% end_if %><% end_loop %>', $data);
+        $this->assertEquals("bob", $result, "Only the last name on the second page is rendered");
+    }
+
     /**
      * Test $Up works when the scope $Up refers to was entered with a "with" block
      */

tests/php/View/SSViewerTest/SSViewerTestModel.php

@@ -7,5 +7,7 @@
 
 class SSViewerTestModel extends DataObject implements TestOnly
 {
-
+    private static array $db = [
+        'Name' => 'Varchar',
+    ];
 }

tests/php/View/SSViewerTest/SSViewerTestModel.yml

@@ -0,0 +1,9 @@
+SilverStripe\View\Tests\SSViewerTest\SSViewerTestModel:
+  test1:
+    Name: steven
+  test2:
+    Name: bonny
+  test3:
+    Name: sam
+  test4:
+    Name: bob