(bug 47950) Fix IndexPager detection of "is first" state

IndexPager currently assumes that if an offset is supplied, then it is
not at the first entry. This is trivially false in many cases, e.g. if
the offset is an older-than date and that date is in the future.

The only way to really determine whether we're at the first entry when
an offset is supplied is to query for 1 row in the opposite direction.
This patch does just that.

Bug: 47950
Change-Id: I05fec226abb609b78a62f2a23f35d5b52a48ab1a

diff --git a/includes/Pager.php b/includes/Pager.php
index 34df830..696c11b 100644 (file)
--- a/includes/Pager.php
+++ b/includes/Pager.php
@@ -206,13 +206,25 @@ abstract class IndexPager extends ContextSource implements Pager {
                # Plus an extra row so that we can tell the "next" link should be shown
                $queryLimit = $this->mLimit + 1;
 
+               if ( $this->mOffset == '' ) {
+                       $isFirst = true;
+               } else {
+                       // If there's an offset, we may or may not be at the first entry.
+                       // The only way to tell is to run the query in the opposite
+                       // direction see if we get a row.
+                       $oldIncludeOffset = $this->mIncludeOffset;
+                       $this->mIncludeOffset = !$this->mIncludeOffset;
+                       $isFirst = !$this->reallyDoQuery( $this->mOffset, 1, !$descending )->numRows();
+                       $this->mIncludeOffset = $oldIncludeOffset;
+               }
+
                $this->mResult = $this->reallyDoQuery(
                        $this->mOffset,
                        $queryLimit,
                        $descending
                );
 
-               $this->extractResultInfo( $this->mOffset, $queryLimit, $this->mResult );
+               $this->extractResultInfo( $isFirst, $queryLimit, $this->mResult );
                $this->mQueryDone = true;
 
                $this->preprocessResults( $this->mResult );
@@ -269,11 +281,12 @@ abstract class IndexPager extends ContextSource implements Pager {
         * Extract some useful data from the result object for use by
         * the navigation bar, put it into $this
         *
-        * @param string $offset index offset, inclusive
+        * @param $isFirst bool: False if there are rows before those fetched (i.e.
+        *     if a "previous" link would make sense)
         * @param $limit Integer: exact query limit
         * @param $res ResultWrapper
         */
-       function extractResultInfo( $offset, $limit, ResultWrapper $res ) {
+       function extractResultInfo( $isFirst, $limit, ResultWrapper $res ) {
                $numRows = $res->numRows();
                if ( $numRows ) {
                        # Remove any table prefix from index field
@@ -311,11 +324,11 @@ abstract class IndexPager extends ContextSource implements Pager {
 
                if ( $this->mIsBackwards ) {
                        $this->mIsFirst = ( $numRows < $limit );
-                       $this->mIsLast = ( $offset == '' );
+                       $this->mIsLast = $isFirst;
                        $this->mLastShown = $firstIndex;
                        $this->mFirstShown = $lastIndex;
                } else {
-                       $this->mIsFirst = ( $offset == '' );
+                       $this->mIsFirst = $isFirst;
                        $this->mIsLast = ( $numRows < $limit );
                        $this->mLastShown = $lastIndex;
                        $this->mFirstShown = $firstIndex;