Merge "Support custom offsets from SearchResultSet"

diff --combined includes/specials/SpecialSearch.php
index e5adeb5,b739c34..eeb8823
--- 1/includes/specials/SpecialSearch.php
--- 2/includes/specials/SpecialSearch.php
+++ b/includes/specials/SpecialSearch.php
@@@ -399,6 -399,7 +399,6 @@@ class SpecialSearch extends SpecialPag
                $mainResultWidget = new FullSearchResultWidget( $this, $linkRenderer );
  
                if ( $search->getFeatureData( 'enable-new-crossproject-page' ) ) {
 -
                        $sidebarResultWidget = new InterwikiSearchResultWidget( $this, $linkRenderer );
                        $sidebarResultsWidget = new InterwikiSearchResultSetWidget(
                                $this,
@@@ -435,9 -436,17 +435,17 @@@
  
                // prev/next links
                if ( $totalRes > $this->limit || $this->offset ) {
+                       // Allow matches to define the correct offset, as interleaved
+                       // AB testing may require a different next page offset.
+                       if ( $textMatches && $textMatches->getOffset() !== null ) {
+                               $offset = $textMatches->getOffset();
+                       } else {
+                               $offset = $this->offset;
+                       }
+ 
                        $prevnext = $this->getLanguage()->viewPrevNext(
                                $this->getPageTitle(),
-                               $this->offset,
+                               $offset,
                                $this->limit,
                                $this->powerSearchOptions() + [ 'search' => $term ],
                                $this->limit + $this->offset >= $totalRes