Fix pagination of fulltext search results

Summary:
Fixes T8285. Fulltext search relies on an underlying engine which can not realistically use cursor paging. This is unusual and creates some oddness.

Tweak a few numbers -- and how offsets are handled -- to separate the filtered offset and unfiltered offset.

Test Plan:
  - Set page size to 2.
  - Ran a query.
  - Paged forward and backward through results sensibly, seeing the full result set.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8285

Differential Revision: https://secure.phabricator.com/D17667

src/__phutil_library_map__.php

@@ -9148,7 +9148,7 @@ phutil_register_library_map(array(
     'PhabricatorSearchDocument' => 'PhabricatorSearchDAO',
     'PhabricatorSearchDocumentField' => 'PhabricatorSearchDAO',
     'PhabricatorSearchDocumentFieldType' => 'Phobject',
-    'PhabricatorSearchDocumentQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
+    'PhabricatorSearchDocumentQuery' => 'PhabricatorPolicyAwareQuery',
     'PhabricatorSearchDocumentRelationship' => 'PhabricatorSearchDAO',
     'PhabricatorSearchDocumentTypeDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorSearchEditController' => 'PhabricatorSearchBaseController',

src/applications/search/query/PhabricatorSearchDocumentQuery.php

@@ -1,10 +1,11 @@
 <?php
 
 final class PhabricatorSearchDocumentQuery
-  extends PhabricatorCursorPagedPolicyAwareQuery {
+  extends PhabricatorPolicyAwareQuery {
 
   private $savedQuery;
   private $objectCapabilities;
+  private $unfilteredOffset;
 
   public function withSavedQuery(PhabricatorSavedQuery $query) {
     $this->savedQuery = $query;
@@ -20,11 +21,27 @@ final class PhabricatorSearchDocumentQuery
     if ($this->objectCapabilities) {
       return $this->objectCapabilities;
     }
+
     return $this->getRequiredCapabilities();
   }
 
+  protected function willExecute() {
+    $this->unfilteredOffset = 0;
+  }
+
   protected function loadPage() {
-    $phids = $this->loadDocumentPHIDsWithoutPolicyChecks();
+    // NOTE: The offset and limit information in the inherited properties of
+    // this object represent a policy-filtered offset and limit, but the
+    // underlying query engine needs an unfiltered offset and limit. We keep
+    // track of an unfiltered result offset internally.
+
+    $query = id(clone($this->savedQuery))
+      ->setParameter('offset', $this->unfilteredOffset)
+      ->setParameter('limit', $this->getRawResultLimit());
+
+    $phids = PhabricatorSearchService::executeSearch($query);
+
+    $this->unfilteredOffset += count($phids);
 
     $handles = id(new PhabricatorHandleQuery())
       ->setViewer($this->getViewer())
@@ -69,25 +86,13 @@ final class PhabricatorSearchDocumentQuery
     return $handles;
   }
 
-  public function loadDocumentPHIDsWithoutPolicyChecks() {
-    $query = id(clone($this->savedQuery))
-      ->setParameter('offset', $this->getOffset())
-      ->setParameter('limit', $this->getRawResultLimit());
-    return PhabricatorSearchService::executeSearch($query);
-  }
-
   public function getQueryApplicationClass() {
     return 'PhabricatorSearchApplication';
   }
 
-  protected function getResultCursor($result) {
-    throw new Exception(
-      pht(
-        'This query does not support cursor paging; it must be offset paged.'));
-  }
-
   protected function nextPage(array $page) {
-    $this->setOffset($this->getOffset() + count($page));
+    // We already updated the internal offset in `loadPage()` after loading
+    // results, so we do not need to make any additional state updates here.
     return $this;
   }
 

src/view/phui/PHUIPagerView.php

@@ -55,7 +55,7 @@ final class PHUIPagerView extends AphrontView {
   }
 
   public function willShowPagingControls() {
-    return $this->hasMorePages;
+    return $this->hasMorePages || $this->getOffset();
   }
 
   public function getHasMorePages() {