Fix off-by-one error in the "previous 200" link in category listings

with until=param

When an until parameter is given i.e. going to a previous page, the
category page does the sql query in descending order. In that case,
the previous page link was given an until paramter that was one more
than the last needed result, since until= is interpreted as up-to but
not including, unlike from=, which is starting from and including.

Bug: 36964
Change-Id: I7eaf58d78136ac069a2d9122bca03f87863d2c0b

diff --git a/includes/CategoryViewer.php b/includes/CategoryViewer.php
index cd9eaa9..1c7e604 100644 (file)
--- a/includes/CategoryViewer.php
+++ b/includes/CategoryViewer.php
@@ -54,6 +54,9 @@ class CategoryViewer extends ContextSource {
        /** @var array */
        protected $nextPage;
 
+       /** @var array */
+       protected $prevPage;
+
        /** @var array */
        protected $flip;
 
@@ -288,6 +291,12 @@ class CategoryViewer extends ContextSource {
                        'subcat' => null,
                        'file' => null,
                );
+               $this->prevPage = array(
+                       'page' => null,
+                       'subcat' => null,
+                       'file' => null,
+               );
+
                $this->flip = array( 'page' => false, 'subcat' => false, 'file' => false );
 
                foreach ( array( 'page', 'subcat', 'file' ) as $type ) {
@@ -344,6 +353,9 @@ class CategoryViewer extends ContextSource {
                                        $this->nextPage[$type] = $humanSortkey;
                                        break;
                                }
+                               if ( $count == $this->limit ) {
+                                       $this->prevPage[$type] = $humanSortkey;
+                               }
 
                                if ( $title->getNamespace() == NS_CATEGORY ) {
                                        $cat = Category::newFromRow( $row, $title );
@@ -458,7 +470,17 @@ class CategoryViewer extends ContextSource {
         */
        private function getSectionPagingLinks( $type ) {
                if ( isset( $this->until[$type] ) && $this->until[$type] !== null ) {
-                       return $this->pagingLinks( $this->nextPage[$type], $this->until[$type], $type );
+                       // The new value for the until parameter should be pointing to the first
+                       // result displayed on the page which is the second last result retrieved
+                       // from the database.The next link should have a from parameter pointing
+                       // to the until parameter of the current page.
+                       if ( $this->nextPage[$type] !== null ) {
+                               return $this->pagingLinks( $this->prevPage[$type], $this->until[$type], $type );
+                       } else {
+                               // If the nextPage variable is null, it means that we have reached the first page
+                               // and therefore the previous link should be disabled.
+                               return $this->pagingLinks( null, $this->until[$type], $type );
+                       }
                } elseif ( $this->nextPage[$type] !== null
                        || ( isset( $this->from[$type] ) && $this->from[$type] !== null )
                ) {