diff --git a/src/applications/search/engineextension/PhabricatorFerretFulltextEngineExtension.php b/src/applications/search/engineextension/PhabricatorFerretFulltextEngineExtension.php
index 766bc4e4c8..8d1b6070e6 100644
--- a/src/applications/search/engineextension/PhabricatorFerretFulltextEngineExtension.php
+++ b/src/applications/search/engineextension/PhabricatorFerretFulltextEngineExtension.php
@@ -1,196 +1,196 @@
 <?php
 
 final class PhabricatorFerretFulltextEngineExtension
   extends PhabricatorFulltextEngineExtension {
 
   const EXTENSIONKEY = 'ferret';
 
 
   public function getExtensionName() {
     return pht('Ferret Fulltext Engine');
   }
 
 
   public function shouldIndexFulltextObject($object) {
     return ($object instanceof PhabricatorFerretInterface);
   }
 
 
   public function indexFulltextObject(
     $object,
     PhabricatorSearchAbstractDocument $document) {
 
     $phid = $document->getPHID();
     $engine = $object->newFerretEngine();
 
     $ferret_document = $engine->newDocumentObject()
       ->setObjectPHID($phid)
       ->setIsClosed(0)
       ->setEpochCreated(0)
       ->setEpochModified(0);
 
     $stemmer = $engine->newStemmer();
 
     // Copy all of the "title" and "body" fields to create new "core" fields.
     // This allows users to search "in title or body" with the "core:" prefix.
     $document_fields = $document->getFieldData();
     $virtual_fields = array();
     foreach ($document_fields as $field) {
       $virtual_fields[] = $field;
 
       list($key, $raw_corpus) = $field;
       switch ($key) {
         case PhabricatorSearchDocumentFieldType::FIELD_TITLE:
         case PhabricatorSearchDocumentFieldType::FIELD_BODY:
           $virtual_fields[] = array(
             PhabricatorSearchDocumentFieldType::FIELD_CORE,
             $raw_corpus,
           );
           break;
       }
     }
 
     $key_all = PhabricatorSearchDocumentFieldType::FIELD_ALL;
 
     $empty_template = array(
       'raw' => array(),
       'term' => array(),
       'normal' => array(),
     );
 
     $ferret_corpus_map = array(
       $key_all => $empty_template,
     );
 
     foreach ($virtual_fields as $field) {
       list($key, $raw_corpus) = $field;
       if (!strlen($raw_corpus)) {
         continue;
       }
 
       $term_corpus = $engine->newTermsCorpus($raw_corpus);
 
       $normal_corpus = $stemmer->stemCorpus($raw_corpus);
-      $normal_coprus = $engine->newTermsCorpus($normal_corpus);
+      $normal_corpus = $engine->newTermsCorpus($normal_corpus);
 
       if (!isset($ferret_corpus_map[$key])) {
         $ferret_corpus_map[$key] = $empty_template;
       }
 
       $ferret_corpus_map[$key]['raw'][] = $raw_corpus;
       $ferret_corpus_map[$key]['term'][] = $term_corpus;
       $ferret_corpus_map[$key]['normal'][] = $normal_corpus;
 
       $ferret_corpus_map[$key_all]['raw'][] = $raw_corpus;
       $ferret_corpus_map[$key_all]['term'][] = $term_corpus;
       $ferret_corpus_map[$key_all]['normal'][] = $normal_corpus;
     }
 
     $ferret_fields = array();
     $ngrams_source = array();
     foreach ($ferret_corpus_map as $key => $fields) {
       $raw_corpus = $fields['raw'];
       $raw_corpus = implode("\n", $raw_corpus);
-      $ngrams_source[] = $raw_corpus;
+      if (strlen($raw_corpus)) {
+        $ngrams_source[] = $raw_corpus;
+      }
 
       $normal_corpus = $fields['normal'];
-      $normal_corpus = implode(' ', $normal_corpus);
+      $normal_corpus = implode("\n", $normal_corpus);
       if (strlen($normal_corpus)) {
         $ngrams_source[] = $normal_corpus;
-        $normal_corpus = ' '.$normal_corpus.' ';
       }
 
       $term_corpus = $fields['term'];
-      $term_corpus = implode(' ', $term_corpus);
+      $term_corpus = implode("\n", $term_corpus);
       if (strlen($term_corpus)) {
         $ngrams_source[] = $term_corpus;
-        $term_corpus = ' '.$term_corpus.' ';
       }
 
       $ferret_fields[] = $engine->newFieldObject()
         ->setFieldKey($key)
         ->setRawCorpus($raw_corpus)
         ->setTermCorpus($term_corpus)
         ->setNormalCorpus($normal_corpus);
     }
-    $ngrams_source = implode(' ', $ngrams_source);
+    $ngrams_source = implode("\n", $ngrams_source);
 
-    $ngrams = $engine->getNgramsFromString($ngrams_source, 'index');
+    $ngrams = $engine->getTermNgramsFromString($ngrams_source);
 
     $ferret_document->openTransaction();
 
     try {
       $this->deleteOldDocument($engine, $object, $document);
 
       $ferret_document->save();
 
       $document_id = $ferret_document->getID();
       foreach ($ferret_fields as $ferret_field) {
         $ferret_field
           ->setDocumentID($document_id)
           ->save();
       }
 
       $ferret_ngrams = $engine->newNgramsObject();
       $conn = $ferret_ngrams->establishConnection('w');
 
       $sql = array();
       foreach ($ngrams as $ngram) {
         $sql[] = qsprintf(
           $conn,
           '(%d, %s)',
           $document_id,
           $ngram);
       }
 
       foreach (PhabricatorLiskDAO::chunkSQL($sql) as $chunk) {
         queryfx(
           $conn,
           'INSERT INTO %T (documentID, ngram) VALUES %Q',
           $ferret_ngrams->getTableName(),
           $chunk);
       }
     } catch (Exception $ex) {
       $ferret_document->killTransaction();
       throw $ex;
     }
 
     $ferret_document->saveTransaction();
   }
 
 
   private function deleteOldDocument(
     PhabricatorFerretEngine $engine,
     $object,
     PhabricatorSearchAbstractDocument $document) {
 
     $old_document = $engine->newDocumentObject()->loadOneWhere(
       'objectPHID = %s',
       $document->getPHID());
     if (!$old_document) {
       return;
     }
 
     $conn = $old_document->establishConnection('w');
     $old_id = $old_document->getID();
 
     queryfx(
       $conn,
       'DELETE FROM %T WHERE id = %d',
       $engine->newDocumentObject()->getTableName(),
       $old_id);
 
     queryfx(
       $conn,
       'DELETE FROM %T WHERE documentID = %d',
       $engine->newFieldObject()->getTableName(),
       $old_id);
 
     queryfx(
       $conn,
       'DELETE FROM %T WHERE documentID = %d',
       $engine->newNgramsObject()->getTableName(),
       $old_id);
   }
 
 }
diff --git a/src/applications/search/ferret/PhabricatorFerretEngine.php b/src/applications/search/ferret/PhabricatorFerretEngine.php
index 3811e16289..5f6470ca20 100644
--- a/src/applications/search/ferret/PhabricatorFerretEngine.php
+++ b/src/applications/search/ferret/PhabricatorFerretEngine.php
@@ -1,102 +1,107 @@
 <?php
 
 abstract class PhabricatorFerretEngine extends Phobject {
 
   abstract public function newNgramsObject();
   abstract public function newDocumentObject();
   abstract public function newFieldObject();
 
   public function newStemmer() {
     return new PhutilSearchStemmer();
   }
 
   public function tokenizeString($value) {
     $value = trim($value, ' ');
     $value = preg_split('/ +/', $value);
     return $value;
   }
 
-  public function getNgramsFromString($value, $mode) {
+  public function getTermNgramsFromString($string) {
+    return $this->getNgramsFromString($string, true);
+  }
+
+  public function getSubstringNgramsFromString($string) {
+    return $this->getNgramsFromString($string, false);
+  }
+
+  private function getNgramsFromString($value, $as_term) {
     $tokens = $this->tokenizeString($value);
 
     $ngrams = array();
     foreach ($tokens as $token) {
       $token = phutil_utf8_strtolower($token);
 
-      switch ($mode) {
-        case 'query':
-          break;
-        case 'index':
-          $token = ' '.$token.' ';
-          break;
-        case 'prefix':
-          $token = ' '.$token;
-          break;
+      if ($as_term) {
+        $token = ' '.$token.' ';
       }
 
       $token_v = phutil_utf8v($token);
       $len = (count($token_v) - 2);
       for ($ii = 0; $ii < $len; $ii++) {
         $ngram = array_slice($token_v, $ii, 3);
         $ngram = implode('', $ngram);
         $ngrams[$ngram] = $ngram;
       }
     }
 
     ksort($ngrams);
 
     return array_keys($ngrams);
   }
 
   public function newTermsCorpus($raw_corpus) {
     $term_corpus = strtr(
       $raw_corpus,
       array(
         '!' => ' ',
         '"' => ' ',
         '#' => ' ',
         '$' => ' ',
         '%' => ' ',
         '&' => ' ',
         '(' => ' ',
         ')' => ' ',
         '*' => ' ',
         '+' => ' ',
         ',' => ' ',
         '-' => ' ',
         '/' => ' ',
         ':' => ' ',
         ';' => ' ',
         '<' => ' ',
         '=' => ' ',
         '>' => ' ',
         '?' => ' ',
         '@' => ' ',
         '[' => ' ',
         '\\' => ' ',
         ']' => ' ',
         '^' => ' ',
         '`' => ' ',
         '{' => ' ',
         '|' => ' ',
         '}' => ' ',
         '~' => ' ',
         '.' => ' ',
         '_' => ' ',
         "\n" => ' ',
         "\r" => ' ',
         "\t" => ' ',
       ));
 
     // NOTE: Single quotes divide terms only if they're at a word boundary.
     // In contractions, like "whom'st've", the entire word is a single term.
     $term_corpus = preg_replace('/(^| )[\']+/', ' ', $term_corpus);
     $term_corpus = preg_replace('/[\']+( |$)/', ' ', $term_corpus);
 
     $term_corpus = preg_replace('/\s+/u', ' ', $term_corpus);
     $term_corpus = trim($term_corpus, ' ');
 
+    if (strlen($term_corpus)) {
+      $term_corpus = ' '.$term_corpus.' ';
+    }
+
     return $term_corpus;
   }
 
 }
diff --git a/src/applications/search/ferret/__tests__/PhabricatorFerretEngineTestCase.php b/src/applications/search/ferret/__tests__/PhabricatorFerretEngineTestCase.php
index b8f1043ab2..a8690f1d8b 100644
--- a/src/applications/search/ferret/__tests__/PhabricatorFerretEngineTestCase.php
+++ b/src/applications/search/ferret/__tests__/PhabricatorFerretEngineTestCase.php
@@ -1,27 +1,27 @@
 <?php
 
 final class PhabricatorFerretEngineTestCase
   extends PhabricatorTestCase {
 
   public function testTermsCorpus() {
     $map = array(
-      'Hear ye, hear ye!' => 'Hear ye hear ye',
-      "Thou whom'st've art worthy." => "Thou whom'st've art worthy",
-      'Guaranteed to contain "food".' => 'Guaranteed to contain food',
+      'Hear ye, hear ye!' => ' Hear ye hear ye ',
+      "Thou whom'st've art worthy." => " Thou whom'st've art worthy ",
+      'Guaranteed to contain "food".' => ' Guaranteed to contain food ',
       'http://example.org/path/to/file.jpg' =>
-        'http example org path to file jpg',
+        ' http example org path to file jpg ',
     );
 
     $engine = new ManiphestTaskFerretEngine();
 
     foreach ($map as $input => $expect) {
       $actual = $engine->newTermsCorpus($input);
 
       $this->assertEqual(
         $expect,
         $actual,
         pht('Terms corpus for: %s', $input));
     }
   }
 
 }
diff --git a/src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php b/src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php
index ccf78de5df..3fdfb33bfe 100644
--- a/src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php
+++ b/src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php
@@ -1,2461 +1,2457 @@
 <?php
 
 /**
  * A query class which uses cursor-based paging. This paging is much more
  * performant than offset-based paging in the presence of policy filtering.
  *
  * @task clauses Building Query Clauses
  * @task appsearch Integration with ApplicationSearch
  * @task customfield Integration with CustomField
  * @task paging Paging
  * @task order Result Ordering
  * @task edgelogic Working with Edge Logic
  * @task spaces Working with Spaces
  */
 abstract class PhabricatorCursorPagedPolicyAwareQuery
   extends PhabricatorPolicyAwareQuery {
 
   private $afterID;
   private $beforeID;
   private $applicationSearchConstraints = array();
   private $internalPaging;
   private $orderVector;
   private $groupVector;
   private $builtinOrder;
   private $edgeLogicConstraints = array();
   private $edgeLogicConstraintsAreValid = false;
   private $spacePHIDs;
   private $spaceIsArchived;
   private $ngrams = array();
   private $ferretEngine;
   private $ferretTokens;
   private $ferretTables;
 
   protected function getPageCursors(array $page) {
     return array(
       $this->getResultCursor(head($page)),
       $this->getResultCursor(last($page)),
     );
   }
 
   protected function getResultCursor($object) {
     if (!is_object($object)) {
       throw new Exception(
         pht(
           'Expected object, got "%s".',
           gettype($object)));
     }
 
     return $object->getID();
   }
 
   protected function nextPage(array $page) {
     // See getPagingViewer() for a description of this flag.
     $this->internalPaging = true;
 
     if ($this->beforeID !== null) {
       $page = array_reverse($page, $preserve_keys = true);
       list($before, $after) = $this->getPageCursors($page);
       $this->beforeID = $before;
     } else {
       list($before, $after) = $this->getPageCursors($page);
       $this->afterID = $after;
     }
   }
 
   final public function setAfterID($object_id) {
     $this->afterID = $object_id;
     return $this;
   }
 
   final protected function getAfterID() {
     return $this->afterID;
   }
 
   final public function setBeforeID($object_id) {
     $this->beforeID = $object_id;
     return $this;
   }
 
   final protected function getBeforeID() {
     return $this->beforeID;
   }
 
   protected function loadStandardPage(PhabricatorLiskDAO $table) {
     $rows = $this->loadStandardPageRows($table);
     return $table->loadAllFromArray($rows);
   }
 
   protected function loadStandardPageRows(PhabricatorLiskDAO $table) {
     $conn = $table->establishConnection('r');
     return $this->loadStandardPageRowsWithConnection(
       $conn,
       $table->getTableName());
   }
 
   protected function loadStandardPageRowsWithConnection(
     AphrontDatabaseConnection $conn,
     $table_name) {
 
     $rows = queryfx_all(
       $conn,
       '%Q FROM %T %Q %Q %Q %Q %Q %Q %Q',
       $this->buildSelectClause($conn),
       $table_name,
       (string)$this->getPrimaryTableAlias(),
       $this->buildJoinClause($conn),
       $this->buildWhereClause($conn),
       $this->buildGroupClause($conn),
       $this->buildHavingClause($conn),
       $this->buildOrderClause($conn),
       $this->buildLimitClause($conn));
 
     return $rows;
   }
 
   /**
    * Get the viewer for making cursor paging queries.
    *
    * NOTE: You should ONLY use this viewer to load cursor objects while
    * building paging queries.
    *
    * Cursor paging can happen in two ways. First, the user can request a page
    * like `/stuff/?after=33`, which explicitly causes paging. Otherwise, we
    * can fall back to implicit paging if we filter some results out of a
    * result list because the user can't see them and need to go fetch some more
    * results to generate a large enough result list.
    *
    * In the first case, want to use the viewer's policies to load the object.
    * This prevents an attacker from figuring out information about an object
    * they can't see by executing queries like `/stuff/?after=33&order=name`,
    * which would otherwise give them a hint about the name of the object.
    * Generally, if a user can't see an object, they can't use it to page.
    *
    * In the second case, we need to load the object whether the user can see
    * it or not, because we need to examine new results. For example, if a user
    * loads `/stuff/` and we run a query for the first 100 items that they can
    * see, but the first 100 rows in the database aren't visible, we need to
    * be able to issue a query for the next 100 results. If we can't load the
    * cursor object, we'll fail or issue the same query over and over again.
    * So, generally, internal paging must bypass policy controls.
    *
    * This method returns the appropriate viewer, based on the context in which
    * the paging is occuring.
    *
    * @return PhabricatorUser Viewer for executing paging queries.
    */
   final protected function getPagingViewer() {
     if ($this->internalPaging) {
       return PhabricatorUser::getOmnipotentUser();
     } else {
       return $this->getViewer();
     }
   }
 
   final protected function buildLimitClause(AphrontDatabaseConnection $conn_r) {
     if ($this->shouldLimitResults()) {
       $limit = $this->getRawResultLimit();
       if ($limit) {
         return qsprintf($conn_r, 'LIMIT %d', $limit);
       }
     }
 
     return '';
   }
 
   protected function shouldLimitResults() {
     return true;
   }
 
   final protected function didLoadResults(array $results) {
     if ($this->beforeID) {
       $results = array_reverse($results, $preserve_keys = true);
     }
     return $results;
   }
 
   final public function executeWithCursorPager(AphrontCursorPagerView $pager) {
     $limit = $pager->getPageSize();
 
     $this->setLimit($limit + 1);
 
     if ($pager->getAfterID()) {
       $this->setAfterID($pager->getAfterID());
     } else if ($pager->getBeforeID()) {
       $this->setBeforeID($pager->getBeforeID());
     }
 
     $results = $this->execute();
     $count = count($results);
 
     $sliced_results = $pager->sliceResults($results);
     if ($sliced_results) {
       list($before, $after) = $this->getPageCursors($sliced_results);
 
       if ($pager->getBeforeID() || ($count > $limit)) {
         $pager->setNextPageID($after);
       }
 
       if ($pager->getAfterID() ||
          ($pager->getBeforeID() && ($count > $limit))) {
         $pager->setPrevPageID($before);
       }
     }
 
     return $sliced_results;
   }
 
 
   /**
    * Return the alias this query uses to identify the primary table.
    *
    * Some automatic query constructions may need to be qualified with a table
    * alias if the query performs joins which make column names ambiguous. If
    * this is the case, return the alias for the primary table the query
    * uses; generally the object table which has `id` and `phid` columns.
    *
    * @return string Alias for the primary table.
    */
   protected function getPrimaryTableAlias() {
     return null;
   }
 
   public function newResultObject() {
     return null;
   }
 
 
 /* -(  Building Query Clauses  )--------------------------------------------- */
 
 
   /**
    * @task clauses
    */
   protected function buildSelectClause(AphrontDatabaseConnection $conn) {
     $parts = $this->buildSelectClauseParts($conn);
     return $this->formatSelectClause($parts);
   }
 
 
   /**
    * @task clauses
    */
   protected function buildSelectClauseParts(AphrontDatabaseConnection $conn) {
     $select = array();
 
     $alias = $this->getPrimaryTableAlias();
     if ($alias) {
       $select[] = qsprintf($conn, '%T.*', $alias);
     } else {
       $select[] = '*';
     }
 
     $select[] = $this->buildEdgeLogicSelectClause($conn);
 
     return $select;
   }
 
 
   /**
    * @task clauses
    */
   protected function buildJoinClause(AphrontDatabaseConnection $conn) {
     $joins = $this->buildJoinClauseParts($conn);
     return $this->formatJoinClause($joins);
   }
 
 
   /**
    * @task clauses
    */
   protected function buildJoinClauseParts(AphrontDatabaseConnection $conn) {
     $joins = array();
     $joins[] = $this->buildEdgeLogicJoinClause($conn);
     $joins[] = $this->buildApplicationSearchJoinClause($conn);
     $joins[] = $this->buildNgramsJoinClause($conn);
     $joins[] = $this->buildFerretJoinClause($conn);
     return $joins;
   }
 
 
   /**
    * @task clauses
    */
   protected function buildWhereClause(AphrontDatabaseConnection $conn) {
     $where = $this->buildWhereClauseParts($conn);
     return $this->formatWhereClause($where);
   }
 
 
   /**
    * @task clauses
    */
   protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
     $where = array();
     $where[] = $this->buildPagingClause($conn);
     $where[] = $this->buildEdgeLogicWhereClause($conn);
     $where[] = $this->buildSpacesWhereClause($conn);
     $where[] = $this->buildNgramsWhereClause($conn);
     $where[] = $this->buildFerretWhereClause($conn);
     return $where;
   }
 
 
   /**
    * @task clauses
    */
   protected function buildHavingClause(AphrontDatabaseConnection $conn) {
     $having = $this->buildHavingClauseParts($conn);
     return $this->formatHavingClause($having);
   }
 
 
   /**
    * @task clauses
    */
   protected function buildHavingClauseParts(AphrontDatabaseConnection $conn) {
     $having = array();
     $having[] = $this->buildEdgeLogicHavingClause($conn);
     return $having;
   }
 
 
   /**
    * @task clauses
    */
   protected function buildGroupClause(AphrontDatabaseConnection $conn) {
     if (!$this->shouldGroupQueryResultRows()) {
       return '';
     }
 
     return qsprintf(
       $conn,
       'GROUP BY %Q',
       $this->getApplicationSearchObjectPHIDColumn());
   }
 
 
   /**
    * @task clauses
    */
   protected function shouldGroupQueryResultRows() {
     if ($this->shouldGroupEdgeLogicResultRows()) {
       return true;
     }
 
     if ($this->getApplicationSearchMayJoinMultipleRows()) {
       return true;
     }
 
     if ($this->shouldGroupNgramResultRows()) {
       return true;
     }
 
     if ($this->shouldGroupFerretResultRows()) {
       return true;
     }
 
     return false;
   }
 
 
 
 /* -(  Paging  )------------------------------------------------------------- */
 
 
   /**
    * @task paging
    */
   protected function buildPagingClause(AphrontDatabaseConnection $conn) {
     $orderable = $this->getOrderableColumns();
     $vector = $this->getOrderVector();
 
     if ($this->beforeID !== null) {
       $cursor = $this->beforeID;
       $reversed = true;
     } else if ($this->afterID !== null) {
       $cursor = $this->afterID;
       $reversed = false;
     } else {
       // No paging is being applied to this query so we do not need to
       // construct a paging clause.
       return '';
     }
 
     $keys = array();
     foreach ($vector as $order) {
       $keys[] = $order->getOrderKey();
     }
 
     $value_map = $this->getPagingValueMap($cursor, $keys);
 
     $columns = array();
     foreach ($vector as $order) {
       $key = $order->getOrderKey();
 
       if (!array_key_exists($key, $value_map)) {
         throw new Exception(
           pht(
             'Query "%s" failed to return a value from getPagingValueMap() '.
             'for column "%s".',
             get_class($this),
             $key));
       }
 
       $column = $orderable[$key];
       $column['value'] = $value_map[$key];
 
       // If the vector component is reversed, we need to reverse whatever the
       // order of the column is.
       if ($order->getIsReversed()) {
         $column['reverse'] = !idx($column, 'reverse', false);
       }
 
       $columns[] = $column;
     }
 
     return $this->buildPagingClauseFromMultipleColumns(
       $conn,
       $columns,
       array(
         'reversed' => $reversed,
       ));
   }
 
 
   /**
    * @task paging
    */
   protected function getPagingValueMap($cursor, array $keys) {
     return array(
       'id' => $cursor,
     );
   }
 
 
   /**
    * @task paging
    */
   protected function loadCursorObject($cursor) {
     $query = newv(get_class($this), array())
       ->setViewer($this->getPagingViewer())
       ->withIDs(array((int)$cursor));
 
     $this->willExecuteCursorQuery($query);
 
     $object = $query->executeOne();
     if (!$object) {
       throw new Exception(
         pht(
           'Cursor "%s" does not identify a valid object in query "%s".',
           $cursor,
           get_class($this)));
     }
 
     return $object;
   }
 
 
   /**
    * @task paging
    */
   protected function willExecuteCursorQuery(
     PhabricatorCursorPagedPolicyAwareQuery $query) {
     return;
   }
 
 
   /**
    * Simplifies the task of constructing a paging clause across multiple
    * columns. In the general case, this looks like:
    *
    *   A > a OR (A = a AND B > b) OR (A = a AND B = b AND C > c)
    *
    * To build a clause, specify the name, type, and value of each column
    * to include:
    *
    *   $this->buildPagingClauseFromMultipleColumns(
    *     $conn_r,
    *     array(
    *       array(
    *         'table' => 't',
    *         'column' => 'title',
    *         'type' => 'string',
    *         'value' => $cursor->getTitle(),
    *         'reverse' => true,
    *       ),
    *       array(
    *         'table' => 't',
    *         'column' => 'id',
    *         'type' => 'int',
    *         'value' => $cursor->getID(),
    *       ),
    *     ),
    *     array(
    *       'reversed' => $is_reversed,
    *     ));
    *
    * This method will then return a composable clause for inclusion in WHERE.
    *
    * @param AphrontDatabaseConnection Connection query will execute on.
    * @param list<map> Column description dictionaries.
    * @param map Additional constuction options.
    * @return string Query clause.
    * @task paging
    */
   final protected function buildPagingClauseFromMultipleColumns(
     AphrontDatabaseConnection $conn,
     array $columns,
     array $options) {
 
     foreach ($columns as $column) {
       PhutilTypeSpec::checkMap(
         $column,
         array(
           'table' => 'optional string|null',
           'column' => 'string',
           'value' => 'wild',
           'type' => 'string',
           'reverse' => 'optional bool',
           'unique' => 'optional bool',
           'null' => 'optional string|null',
         ));
     }
 
     PhutilTypeSpec::checkMap(
       $options,
       array(
         'reversed' => 'optional bool',
       ));
 
     $is_query_reversed = idx($options, 'reversed', false);
 
     $clauses = array();
     $accumulated = array();
     $last_key = last_key($columns);
     foreach ($columns as $key => $column) {
       $type = $column['type'];
 
       $null = idx($column, 'null');
       if ($column['value'] === null) {
         if ($null) {
           $value = null;
         } else {
           throw new Exception(
             pht(
               'Column "%s" has null value, but does not specify a null '.
               'behavior.',
               $key));
         }
       } else {
         switch ($type) {
           case 'int':
             $value = qsprintf($conn, '%d', $column['value']);
             break;
           case 'float':
             $value = qsprintf($conn, '%f', $column['value']);
             break;
           case 'string':
             $value = qsprintf($conn, '%s', $column['value']);
             break;
           default:
             throw new Exception(
               pht(
                 'Column "%s" has unknown column type "%s".',
                 $column['column'],
                 $type));
         }
       }
 
       $is_column_reversed = idx($column, 'reverse', false);
       $reverse = ($is_query_reversed xor $is_column_reversed);
 
       $clause = $accumulated;
 
       $table_name = idx($column, 'table');
       $column_name = $column['column'];
       if ($table_name !== null) {
         $field = qsprintf($conn, '%T.%T', $table_name, $column_name);
       } else {
         $field = qsprintf($conn, '%T', $column_name);
       }
 
       $parts = array();
       if ($null) {
         $can_page_if_null = ($null === 'head');
         $can_page_if_nonnull = ($null === 'tail');
 
         if ($reverse) {
           $can_page_if_null = !$can_page_if_null;
           $can_page_if_nonnull = !$can_page_if_nonnull;
         }
 
         $subclause = null;
         if ($can_page_if_null && $value === null) {
           $parts[] = qsprintf(
             $conn,
             '(%Q IS NOT NULL)',
             $field);
         } else if ($can_page_if_nonnull && $value !== null) {
           $parts[] = qsprintf(
             $conn,
             '(%Q IS NULL)',
             $field);
         }
       }
 
       if ($value !== null) {
         $parts[] = qsprintf(
           $conn,
           '%Q %Q %Q',
           $field,
           $reverse ? '>' : '<',
           $value);
       }
 
       if ($parts) {
         if (count($parts) > 1) {
           $clause[] = '('.implode(') OR (', $parts).')';
         } else {
           $clause[] = head($parts);
         }
       }
 
       if ($clause) {
         if (count($clause) > 1) {
           $clauses[] = '('.implode(') AND (', $clause).')';
         } else {
           $clauses[] = head($clause);
         }
       }
 
       if ($value === null) {
         $accumulated[] = qsprintf(
           $conn,
           '%Q IS NULL',
           $field);
       } else {
         $accumulated[] = qsprintf(
           $conn,
           '%Q = %Q',
           $field,
           $value);
       }
     }
 
     return '('.implode(') OR (', $clauses).')';
   }
 
 
 /* -(  Result Ordering  )---------------------------------------------------- */
 
 
   /**
    * Select a result ordering.
    *
    * This is a high-level method which selects an ordering from a predefined
    * list of builtin orders, as provided by @{method:getBuiltinOrders}. These
    * options are user-facing and not exhaustive, but are generally convenient
    * and meaningful.
    *
    * You can also use @{method:setOrderVector} to specify a low-level ordering
    * across individual orderable columns. This offers greater control but is
    * also more involved.
    *
    * @param string Key of a builtin order supported by this query.
    * @return this
    * @task order
    */
   public function setOrder($order) {
     $aliases = $this->getBuiltinOrderAliasMap();
 
     if (empty($aliases[$order])) {
       throw new Exception(
         pht(
           'Query "%s" does not support a builtin order "%s". Supported orders '.
           'are: %s.',
           get_class($this),
           $order,
           implode(', ', array_keys($aliases))));
     }
 
     $this->builtinOrder = $aliases[$order];
     $this->orderVector = null;
 
     return $this;
   }
 
 
   /**
    * Set a grouping order to apply before primary result ordering.
    *
    * This allows you to preface the query order vector with additional orders,
    * so you can effect "group by" queries while still respecting "order by".
    *
    * This is a high-level method which works alongside @{method:setOrder}. For
    * lower-level control over order vectors, use @{method:setOrderVector}.
    *
    * @param PhabricatorQueryOrderVector|list<string> List of order keys.
    * @return this
    * @task order
    */
   public function setGroupVector($vector) {
     $this->groupVector = $vector;
     $this->orderVector = null;
 
     return $this;
   }
 
 
   /**
    * Get builtin orders for this class.
    *
    * In application UIs, we want to be able to present users with a small
    * selection of meaningful order options (like "Order by Title") rather than
    * an exhaustive set of column ordering options.
    *
    * Meaningful user-facing orders are often really orders across multiple
    * columns: for example, a "title" ordering is usually implemented as a
    * "title, id" ordering under the hood.
    *
    * Builtin orders provide a mapping from convenient, understandable
    * user-facing orders to implementations.
    *
    * A builtin order should provide these keys:
    *
    *   - `vector` (`list<string>`): The actual order vector to use.
    *   - `name` (`string`): Human-readable order name.
    *
    * @return map<string, wild> Map from builtin order keys to specification.
    * @task order
    */
   public function getBuiltinOrders() {
     $orders = array(
       'newest' => array(
         'vector' => array('id'),
         'name' => pht('Creation (Newest First)'),
         'aliases' => array('created'),
       ),
       'oldest' => array(
         'vector' => array('-id'),
         'name' => pht('Creation (Oldest First)'),
       ),
     );
 
     $object = $this->newResultObject();
     if ($object instanceof PhabricatorCustomFieldInterface) {
       $list = PhabricatorCustomField::getObjectFields(
         $object,
         PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
       foreach ($list->getFields() as $field) {
         $index = $field->buildOrderIndex();
         if (!$index) {
           continue;
         }
 
         $legacy_key = 'custom:'.$field->getFieldKey();
         $modern_key = $field->getModernFieldKey();
 
         $orders[$modern_key] = array(
           'vector' => array($modern_key, 'id'),
           'name' => $field->getFieldName(),
           'aliases' => array($legacy_key),
         );
 
         $orders['-'.$modern_key] = array(
           'vector' => array('-'.$modern_key, '-id'),
           'name' => pht('%s (Reversed)', $field->getFieldName()),
         );
       }
     }
 
     return $orders;
   }
 
   public function getBuiltinOrderAliasMap() {
     $orders = $this->getBuiltinOrders();
 
     $map = array();
     foreach ($orders as $key => $order) {
       $keys = array();
       $keys[] = $key;
       foreach (idx($order, 'aliases', array()) as $alias) {
         $keys[] = $alias;
       }
 
       foreach ($keys as $alias) {
         if (isset($map[$alias])) {
           throw new Exception(
             pht(
               'Two builtin orders ("%s" and "%s") define the same key or '.
               'alias ("%s"). Each order alias and key must be unique and '.
               'identify a single order.',
               $key,
               $map[$alias],
               $alias));
         }
         $map[$alias] = $key;
       }
     }
 
     return $map;
   }
 
 
   /**
    * Set a low-level column ordering.
    *
    * This is a low-level method which offers granular control over column
    * ordering. In most cases, applications can more easily use
    * @{method:setOrder} to choose a high-level builtin order.
    *
    * To set an order vector, specify a list of order keys as provided by
    * @{method:getOrderableColumns}.
    *
    * @param PhabricatorQueryOrderVector|list<string> List of order keys.
    * @return this
    * @task order
    */
   public function setOrderVector($vector) {
     $vector = PhabricatorQueryOrderVector::newFromVector($vector);
 
     $orderable = $this->getOrderableColumns();
 
     // Make sure that all the components identify valid columns.
     $unique = array();
     foreach ($vector as $order) {
       $key = $order->getOrderKey();
       if (empty($orderable[$key])) {
         $valid = implode(', ', array_keys($orderable));
         throw new Exception(
           pht(
             'This query ("%s") does not support sorting by order key "%s". '.
             'Supported orders are: %s.',
             get_class($this),
             $key,
             $valid));
       }
 
       $unique[$key] = idx($orderable[$key], 'unique', false);
     }
 
     // Make sure that the last column is unique so that this is a strong
     // ordering which can be used for paging.
     $last = last($unique);
     if ($last !== true) {
       throw new Exception(
         pht(
           'Order vector "%s" is invalid: the last column in an order must '.
           'be a column with unique values, but "%s" is not unique.',
           $vector->getAsString(),
           last_key($unique)));
     }
 
     // Make sure that other columns are not unique; an ordering like "id, name"
     // does not make sense because only "id" can ever have an effect.
     array_pop($unique);
     foreach ($unique as $key => $is_unique) {
       if ($is_unique) {
         throw new Exception(
           pht(
             'Order vector "%s" is invalid: only the last column in an order '.
             'may be unique, but "%s" is a unique column and not the last '.
             'column in the order.',
             $vector->getAsString(),
             $key));
       }
     }
 
     $this->orderVector = $vector;
     return $this;
   }
 
 
   /**
    * Get the effective order vector.
    *
    * @return PhabricatorQueryOrderVector Effective vector.
    * @task order
    */
   protected function getOrderVector() {
     if (!$this->orderVector) {
       if ($this->builtinOrder !== null) {
         $builtin_order = idx($this->getBuiltinOrders(), $this->builtinOrder);
         $vector = $builtin_order['vector'];
       } else {
         $vector = $this->getDefaultOrderVector();
       }
 
       if ($this->groupVector) {
         $group = PhabricatorQueryOrderVector::newFromVector($this->groupVector);
         $group->appendVector($vector);
         $vector = $group;
       }
 
       $vector = PhabricatorQueryOrderVector::newFromVector($vector);
 
       // We call setOrderVector() here to apply checks to the default vector.
       // This catches any errors in the implementation.
       $this->setOrderVector($vector);
     }
 
     return $this->orderVector;
   }
 
 
   /**
    * @task order
    */
   protected function getDefaultOrderVector() {
     return array('id');
   }
 
 
   /**
    * @task order
    */
   public function getOrderableColumns() {
     $cache = PhabricatorCaches::getRequestCache();
     $class = get_class($this);
     $cache_key = 'query.orderablecolumns.'.$class;
 
     $columns = $cache->getKey($cache_key);
     if ($columns !== null) {
       return $columns;
     }
 
     $columns = array(
       'id' => array(
         'table' => $this->getPrimaryTableAlias(),
         'column' => 'id',
         'reverse' => false,
         'type' => 'int',
         'unique' => true,
       ),
     );
 
     $object = $this->newResultObject();
     if ($object instanceof PhabricatorCustomFieldInterface) {
       $list = PhabricatorCustomField::getObjectFields(
         $object,
         PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
       foreach ($list->getFields() as $field) {
         $index = $field->buildOrderIndex();
         if (!$index) {
           continue;
         }
 
         $digest = $field->getFieldIndex();
 
         $key = $field->getModernFieldKey();
 
         $columns[$key] = array(
           'table' => 'appsearch_order_'.$digest,
           'column' => 'indexValue',
           'type' => $index->getIndexValueType(),
           'null' => 'tail',
           'customfield' => true,
           'customfield.index.table' => $index->getTableName(),
           'customfield.index.key' => $digest,
         );
       }
     }
 
     $cache->setKey($cache_key, $columns);
 
     return $columns;
   }
 
 
   /**
    * @task order
    */
   final protected function buildOrderClause(AphrontDatabaseConnection $conn) {
     $orderable = $this->getOrderableColumns();
     $vector = $this->getOrderVector();
 
     $parts = array();
     foreach ($vector as $order) {
       $part = $orderable[$order->getOrderKey()];
       if ($order->getIsReversed()) {
         $part['reverse'] = !idx($part, 'reverse', false);
       }
       $parts[] = $part;
     }
 
     return $this->formatOrderClause($conn, $parts);
   }
 
 
   /**
    * @task order
    */
   protected function formatOrderClause(
     AphrontDatabaseConnection $conn,
     array $parts) {
 
     $is_query_reversed = false;
     if ($this->getBeforeID()) {
       $is_query_reversed = !$is_query_reversed;
     }
 
     $sql = array();
     foreach ($parts as $key => $part) {
       $is_column_reversed = !empty($part['reverse']);
 
       $descending = true;
       if ($is_query_reversed) {
         $descending = !$descending;
       }
 
       if ($is_column_reversed) {
         $descending = !$descending;
       }
 
       $table = idx($part, 'table');
       $column = $part['column'];
 
       if ($table !== null) {
         $field = qsprintf($conn, '%T.%T', $table, $column);
       } else {
         $field = qsprintf($conn, '%T', $column);
       }
 
       $null = idx($part, 'null');
       if ($null) {
         switch ($null) {
           case 'head':
             $null_field = qsprintf($conn, '(%Q IS NULL)', $field);
             break;
           case 'tail':
             $null_field = qsprintf($conn, '(%Q IS NOT NULL)', $field);
             break;
           default:
             throw new Exception(
               pht(
                 'NULL value "%s" is invalid. Valid values are "head" and '.
                 '"tail".',
                 $null));
         }
 
         if ($descending) {
           $sql[] = qsprintf($conn, '%Q DESC', $null_field);
         } else {
           $sql[] = qsprintf($conn, '%Q ASC', $null_field);
         }
       }
 
       if ($descending) {
         $sql[] = qsprintf($conn, '%Q DESC', $field);
       } else {
         $sql[] = qsprintf($conn, '%Q ASC', $field);
       }
     }
 
     return qsprintf($conn, 'ORDER BY %Q', implode(', ', $sql));
   }
 
 
 /* -(  Application Search  )------------------------------------------------- */
 
 
   /**
    * Constrain the query with an ApplicationSearch index, requiring field values
    * contain at least one of the values in a set.
    *
    * This constraint can build the most common types of queries, like:
    *
    *   - Find users with shirt sizes "X" or "XL".
    *   - Find shoes with size "13".
    *
    * @param PhabricatorCustomFieldIndexStorage Table where the index is stored.
    * @param string|list<string> One or more values to filter by.
    * @return this
    * @task appsearch
    */
   public function withApplicationSearchContainsConstraint(
     PhabricatorCustomFieldIndexStorage $index,
     $value) {
 
     $this->applicationSearchConstraints[] = array(
       'type'  => $index->getIndexValueType(),
       'cond'  => '=',
       'table' => $index->getTableName(),
       'index' => $index->getIndexKey(),
       'value' => $value,
     );
 
     return $this;
   }
 
 
   /**
    * Constrain the query with an ApplicationSearch index, requiring values
    * exist in a given range.
    *
    * This constraint is useful for expressing date ranges:
    *
    *   - Find events between July 1st and July 7th.
    *
    * The ends of the range are inclusive, so a `$min` of `3` and a `$max` of
    * `5` will match fields with values `3`, `4`, or `5`. Providing `null` for
    * either end of the range will leave that end of the constraint open.
    *
    * @param PhabricatorCustomFieldIndexStorage Table where the index is stored.
    * @param int|null Minimum permissible value, inclusive.
    * @param int|null Maximum permissible value, inclusive.
    * @return this
    * @task appsearch
    */
   public function withApplicationSearchRangeConstraint(
     PhabricatorCustomFieldIndexStorage $index,
     $min,
     $max) {
 
     $index_type = $index->getIndexValueType();
     if ($index_type != 'int') {
       throw new Exception(
         pht(
           'Attempting to apply a range constraint to a field with index type '.
           '"%s", expected type "%s".',
           $index_type,
           'int'));
     }
 
     $this->applicationSearchConstraints[] = array(
       'type' => $index->getIndexValueType(),
       'cond' => 'range',
       'table' => $index->getTableName(),
       'index' => $index->getIndexKey(),
       'value' => array($min, $max),
     );
 
     return $this;
   }
 
 
   /**
    * Get the name of the query's primary object PHID column, for constructing
    * JOIN clauses. Normally (and by default) this is just `"phid"`, but it may
    * be something more exotic.
    *
    * See @{method:getPrimaryTableAlias} if the column needs to be qualified with
    * a table alias.
    *
    * @return string Column name.
    * @task appsearch
    */
   protected function getApplicationSearchObjectPHIDColumn() {
     if ($this->getPrimaryTableAlias()) {
       $prefix = $this->getPrimaryTableAlias().'.';
     } else {
       $prefix = '';
     }
 
     return $prefix.'phid';
   }
 
 
   /**
    * Determine if the JOINs built by ApplicationSearch might cause each primary
    * object to return multiple result rows. Generally, this means the query
    * needs an extra GROUP BY clause.
    *
    * @return bool True if the query may return multiple rows for each object.
    * @task appsearch
    */
   protected function getApplicationSearchMayJoinMultipleRows() {
     foreach ($this->applicationSearchConstraints as $constraint) {
       $type = $constraint['type'];
       $value = $constraint['value'];
       $cond = $constraint['cond'];
 
       switch ($cond) {
         case '=':
           switch ($type) {
             case 'string':
             case 'int':
               if (count((array)$value) > 1) {
                 return true;
               }
               break;
             default:
               throw new Exception(pht('Unknown index type "%s"!', $type));
           }
           break;
         case 'range':
           // NOTE: It's possible to write a custom field where multiple rows
           // match a range constraint, but we don't currently ship any in the
           // upstream and I can't immediately come up with cases where this
           // would make sense.
           break;
         default:
           throw new Exception(pht('Unknown constraint condition "%s"!', $cond));
       }
     }
 
     return false;
   }
 
 
   /**
    * Construct a GROUP BY clause appropriate for ApplicationSearch constraints.
    *
    * @param AphrontDatabaseConnection Connection executing the query.
    * @return string Group clause.
    * @task appsearch
    */
   protected function buildApplicationSearchGroupClause(
     AphrontDatabaseConnection $conn_r) {
 
     if ($this->getApplicationSearchMayJoinMultipleRows()) {
       return qsprintf(
         $conn_r,
         'GROUP BY %Q',
         $this->getApplicationSearchObjectPHIDColumn());
     } else {
       return '';
     }
   }
 
 
   /**
    * Construct a JOIN clause appropriate for applying ApplicationSearch
    * constraints.
    *
    * @param AphrontDatabaseConnection Connection executing the query.
    * @return string Join clause.
    * @task appsearch
    */
   protected function buildApplicationSearchJoinClause(
     AphrontDatabaseConnection $conn_r) {
 
     $joins = array();
     foreach ($this->applicationSearchConstraints as $key => $constraint) {
       $table = $constraint['table'];
       $alias = 'appsearch_'.$key;
       $index = $constraint['index'];
       $cond = $constraint['cond'];
       $phid_column = $this->getApplicationSearchObjectPHIDColumn();
       switch ($cond) {
         case '=':
           $type = $constraint['type'];
           switch ($type) {
             case 'string':
               $constraint_clause = qsprintf(
                 $conn_r,
                 '%T.indexValue IN (%Ls)',
                 $alias,
                 (array)$constraint['value']);
               break;
             case 'int':
               $constraint_clause = qsprintf(
                 $conn_r,
                 '%T.indexValue IN (%Ld)',
                 $alias,
                 (array)$constraint['value']);
               break;
             default:
               throw new Exception(pht('Unknown index type "%s"!', $type));
           }
 
           $joins[] = qsprintf(
             $conn_r,
             'JOIN %T %T ON %T.objectPHID = %Q
               AND %T.indexKey = %s
               AND (%Q)',
             $table,
             $alias,
             $alias,
             $phid_column,
             $alias,
             $index,
             $constraint_clause);
           break;
         case 'range':
           list($min, $max) = $constraint['value'];
           if (($min === null) && ($max === null)) {
             // If there's no actual range constraint, just move on.
             break;
           }
 
           if ($min === null) {
             $constraint_clause = qsprintf(
               $conn_r,
               '%T.indexValue <= %d',
               $alias,
               $max);
           } else if ($max === null) {
             $constraint_clause = qsprintf(
               $conn_r,
               '%T.indexValue >= %d',
               $alias,
               $min);
           } else {
             $constraint_clause = qsprintf(
               $conn_r,
               '%T.indexValue BETWEEN %d AND %d',
               $alias,
               $min,
               $max);
           }
 
           $joins[] = qsprintf(
             $conn_r,
             'JOIN %T %T ON %T.objectPHID = %Q
               AND %T.indexKey = %s
               AND (%Q)',
             $table,
             $alias,
             $alias,
             $phid_column,
             $alias,
             $index,
             $constraint_clause);
           break;
         default:
           throw new Exception(pht('Unknown constraint condition "%s"!', $cond));
       }
     }
 
     $phid_column = $this->getApplicationSearchObjectPHIDColumn();
     $orderable = $this->getOrderableColumns();
 
     $vector = $this->getOrderVector();
     foreach ($vector as $order) {
       $spec = $orderable[$order->getOrderKey()];
       if (empty($spec['customfield'])) {
         continue;
       }
 
       $table = $spec['customfield.index.table'];
       $alias = $spec['table'];
       $key = $spec['customfield.index.key'];
 
       $joins[] = qsprintf(
         $conn_r,
         'LEFT JOIN %T %T ON %T.objectPHID = %Q
           AND %T.indexKey = %s',
         $table,
         $alias,
         $alias,
         $phid_column,
         $alias,
         $key);
     }
 
     return implode(' ', $joins);
   }
 
 
 /* -(  Integration with CustomField  )--------------------------------------- */
 
 
   /**
    * @task customfield
    */
   protected function getPagingValueMapForCustomFields(
     PhabricatorCustomFieldInterface $object) {
 
     // We have to get the current field values on the cursor object.
     $fields = PhabricatorCustomField::getObjectFields(
       $object,
       PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
     $fields->setViewer($this->getViewer());
     $fields->readFieldsFromStorage($object);
 
     $map = array();
     foreach ($fields->getFields() as $field) {
       $map['custom:'.$field->getFieldKey()] = $field->getValueForStorage();
     }
 
     return $map;
   }
 
 
   /**
    * @task customfield
    */
   protected function isCustomFieldOrderKey($key) {
     $prefix = 'custom:';
     return !strncmp($key, $prefix, strlen($prefix));
   }
 
 
 /* -(  Ferret  )------------------------------------------------------------- */
 
 
   public function withFerretConstraint(
     PhabricatorFerretEngine $engine,
     array $fulltext_tokens) {
 
     if ($this->ferretEngine) {
       throw new Exception(
         pht(
           'Query may not have multiple fulltext constraints.'));
     }
 
     if (!$fulltext_tokens) {
       return $this;
     }
 
     $this->ferretEngine = $engine;
     $this->ferretTokens = $fulltext_tokens;
 
 
     $function_map = array(
       'all' => PhabricatorSearchDocumentFieldType::FIELD_ALL,
       'title' => PhabricatorSearchDocumentFieldType::FIELD_TITLE,
       'body' => PhabricatorSearchDocumentFieldType::FIELD_BODY,
       'core' => PhabricatorSearchDocumentFieldType::FIELD_CORE,
     );
 
     $current_function = 'all';
     $table_map = array();
     $idx = 1;
     foreach ($this->ferretTokens as $fulltext_token) {
       $raw_token = $fulltext_token->getToken();
       $function = $raw_token->getFunction();
 
       if ($function === null) {
         $function = $current_function;
       }
 
       if (!isset($function_map[$function])) {
         throw new PhutilSearchQueryCompilerSyntaxException(
           pht(
             'Unknown search function "%s".',
             $function));
       }
 
       if (!isset($table_map[$function])) {
         $alias = 'ftfield'.$idx++;
         $table_map[$function] = array(
           'alias' => $alias,
           'key' => $function_map[$function],
         );
       }
 
       $current_function = $function;
     }
 
     $this->ferretTables = $table_map;
 
     return $this;
   }
 
   protected function buildFerretJoinClause(AphrontDatabaseConnection $conn) {
     if (!$this->ferretEngine) {
       return array();
     }
 
     $op_sub = PhutilSearchQueryCompiler::OPERATOR_SUBSTRING;
     $op_not = PhutilSearchQueryCompiler::OPERATOR_NOT;
 
     $engine = $this->ferretEngine;
     $stemmer = $engine->newStemmer();
 
     $ngram_table = $engine->newNgramsObject();
     $ngram_table_name = $ngram_table->getTableName();
 
     $flat = array();
     foreach ($this->ferretTokens as $fulltext_token) {
       $raw_token = $fulltext_token->getToken();
 
       // If this is a negated term like "-pomegranate", don't join the ngram
       // table since we aren't looking for documents with this term. (We could
       // LEFT JOIN the table and require a NULL row, but this is probably more
       // trouble than it's worth.)
       if ($raw_token->getOperator() == $op_not) {
         continue;
       }
 
       $value = $raw_token->getValue();
 
       $length = count(phutil_utf8v($value));
 
       if ($raw_token->getOperator() == $op_sub) {
         $is_substring = true;
       } else {
         $is_substring = false;
       }
 
       // If the user specified a substring query for a substring which is
       // shorter than the ngram length, we can't use the ngram index, so
       // don't do a join. We'll fall back to just doing LIKE on the full
       // corpus.
       if ($is_substring) {
         if ($length < 3) {
           continue;
         }
       }
 
       if ($raw_token->isQuoted()) {
         $is_stemmed = false;
       } else {
         $is_stemmed = true;
       }
 
       if ($is_substring) {
-        $ngrams = $engine->getNgramsFromString($value, 'query');
+        $ngrams = $engine->getSubstringNgramsFromString($value);
       } else {
-        $ngrams = $engine->getNgramsFromString($value, 'index');
+        $ngrams = $engine->getTermNgramsFromString($value);
 
         // If this is a stemmed term, only look for ngrams present in both the
         // unstemmed and stemmed variations.
         if ($is_stemmed) {
           $stem_value = $stemmer->stemToken($value);
-          $stem_ngrams = $engine->getNgramsFromString(
-            $stem_value,
-            'index');
-
+          $stem_ngrams = $engine->getTermNgramsFromString($stem_value);
           $ngrams = array_intersect($ngrams, $stem_ngrams);
         }
       }
 
       foreach ($ngrams as $ngram) {
         $flat[] = array(
           'table' => $ngram_table_name,
           'ngram' => $ngram,
         );
       }
     }
 
     // MySQL only allows us to join a maximum of 61 tables per query. Each
     // ngram is going to cost us a join toward that limit, so if the user
     // specified a very long query string, just pick 16 of the ngrams
     // at random.
     if (count($flat) > 16) {
       shuffle($flat);
       $flat = array_slice($flat, 0, 16);
     }
 
     $alias = $this->getPrimaryTableAlias();
     if ($alias) {
       $phid_column = qsprintf($conn, '%T.%T', $alias, 'phid');
     } else {
       $phid_column = qsprintf($conn, '%T', 'phid');
     }
 
     $document_table = $engine->newDocumentObject();
     $field_table = $engine->newFieldObject();
 
     $joins = array();
     $joins[] = qsprintf(
       $conn,
       'JOIN %T ftdoc ON ftdoc.objectPHID = %Q',
       $document_table->getTableName(),
       $phid_column);
 
     $idx = 1;
     foreach ($flat as $spec) {
       $table = $spec['table'];
       $ngram = $spec['ngram'];
 
       $alias = 'ft'.$idx++;
 
       $joins[] = qsprintf(
         $conn,
         'JOIN %T %T ON %T.documentID = ftdoc.id AND %T.ngram = %s',
         $table,
         $alias,
         $alias,
         $alias,
         $ngram);
     }
 
     foreach ($this->ferretTables as $table) {
       $alias = $table['alias'];
 
       $joins[] = qsprintf(
         $conn,
         'JOIN %T %T ON ftdoc.id = %T.documentID
           AND %T.fieldKey = %s',
         $field_table->getTableName(),
         $alias,
         $alias,
         $alias,
         $table['key']);
     }
 
     return $joins;
   }
 
   protected function buildFerretWhereClause(AphrontDatabaseConnection $conn) {
     if (!$this->ferretEngine) {
       return array();
     }
 
     $engine = $this->ferretEngine;
     $stemmer = $engine->newStemmer();
     $table_map = $this->ferretTables;
 
     $op_sub = PhutilSearchQueryCompiler::OPERATOR_SUBSTRING;
     $op_not = PhutilSearchQueryCompiler::OPERATOR_NOT;
 
     $where = array();
     $current_function = 'all';
     foreach ($this->ferretTokens as $fulltext_token) {
       $raw_token = $fulltext_token->getToken();
       $value = $raw_token->getValue();
 
       $function = $raw_token->getFunction();
       if ($function === null) {
         $function = $current_function;
       }
       $current_function = $function;
 
       $table_alias = $table_map[$function]['alias'];
 
       $is_not = ($raw_token->getOperator() == $op_not);
 
       if ($raw_token->getOperator() == $op_sub) {
         $is_substring = true;
       } else {
         $is_substring = false;
       }
 
       // If we're doing substring search, we just match against the raw corpus
       // and we're done.
       if ($is_substring) {
         if ($is_not) {
           $where[] = qsprintf(
             $conn,
             '(%T.rawCorpus NOT LIKE %~)',
             $table_alias,
             $value);
         } else {
           $where[] = qsprintf(
             $conn,
             '(%T.rawCorpus LIKE %~)',
             $table_alias,
             $value);
         }
         continue;
       }
 
       // Otherwise, we need to match against the term corpus and the normal
       // corpus, so that searching for "raw" does not find "strawberry".
       if ($raw_token->isQuoted()) {
         $is_quoted = true;
         $is_stemmed = false;
       } else {
         $is_quoted = false;
         $is_stemmed = true;
       }
 
       // Never stem negated queries, since this can exclude results users
       // did not mean to exclude and generally confuse things.
       if ($is_not) {
         $is_stemmed = false;
       }
 
       $term_constraints = array();
 
-      $term_value = ' '.$engine->newTermsCorpus($value).' ';
+      $term_value = $engine->newTermsCorpus($value);
       if ($is_not) {
         $term_constraints[] = qsprintf(
           $conn,
           '(%T.termCorpus NOT LIKE %~)',
           $table_alias,
           $term_value);
       } else {
         $term_constraints[] = qsprintf(
           $conn,
           '(%T.termCorpus LIKE %~)',
           $table_alias,
           $term_value);
       }
 
       if ($is_stemmed) {
         $stem_value = $stemmer->stemToken($value);
         $stem_value = $engine->newTermsCorpus($stem_value);
-        $stem_value = ' '.$stem_value.' ';
 
         $term_constraints[] = qsprintf(
           $conn,
           '(%T.normalCorpus LIKE %~)',
           $table_alias,
           $stem_value);
       }
 
       if ($is_not) {
         $where[] = qsprintf(
           $conn,
           '(%Q)',
           implode(' AND ', $term_constraints));
       } else if ($is_quoted) {
         $where[] = qsprintf(
           $conn,
           '(%T.rawCorpus LIKE %~ AND (%Q))',
           $table_alias,
           $value,
           implode(' OR ', $term_constraints));
       } else {
         $where[] = qsprintf(
           $conn,
           '(%Q)',
           implode(' OR ', $term_constraints));
       }
     }
 
     return $where;
   }
 
   protected function shouldGroupFerretResultRows() {
     return (bool)$this->ferretTokens;
   }
 
 
 /* -(  Ngrams  )------------------------------------------------------------- */
 
 
   protected function withNgramsConstraint(
     PhabricatorSearchNgrams $index,
     $value) {
 
     if (strlen($value)) {
       $this->ngrams[] = array(
         'index' => $index,
         'value' => $value,
         'length' => count(phutil_utf8v($value)),
       );
     }
 
     return $this;
   }
 
 
   protected function buildNgramsJoinClause(AphrontDatabaseConnection $conn) {
     $flat = array();
     foreach ($this->ngrams as $spec) {
       $index = $spec['index'];
       $value = $spec['value'];
       $length = $spec['length'];
 
       if ($length >= 3) {
         $ngrams = $index->getNgramsFromString($value, 'query');
         $prefix = false;
       } else if ($length == 2) {
         $ngrams = $index->getNgramsFromString($value, 'prefix');
         $prefix = false;
       } else {
         $ngrams = array(' '.$value);
         $prefix = true;
       }
 
       foreach ($ngrams as $ngram) {
         $flat[] = array(
           'table' => $index->getTableName(),
           'ngram' => $ngram,
           'prefix' => $prefix,
         );
       }
     }
 
     // MySQL only allows us to join a maximum of 61 tables per query. Each
     // ngram is going to cost us a join toward that limit, so if the user
     // specified a very long query string, just pick 16 of the ngrams
     // at random.
     if (count($flat) > 16) {
       shuffle($flat);
       $flat = array_slice($flat, 0, 16);
     }
 
     $alias = $this->getPrimaryTableAlias();
     if ($alias) {
       $id_column = qsprintf($conn, '%T.%T', $alias, 'id');
     } else {
       $id_column = qsprintf($conn, '%T', 'id');
     }
 
     $idx = 1;
     $joins = array();
     foreach ($flat as $spec) {
       $table = $spec['table'];
       $ngram = $spec['ngram'];
       $prefix = $spec['prefix'];
 
       $alias = 'ngm'.$idx++;
 
       if ($prefix) {
         $joins[] = qsprintf(
           $conn,
           'JOIN %T %T ON %T.objectID = %Q AND %T.ngram LIKE %>',
           $table,
           $alias,
           $alias,
           $id_column,
           $alias,
           $ngram);
       } else {
         $joins[] = qsprintf(
           $conn,
           'JOIN %T %T ON %T.objectID = %Q AND %T.ngram = %s',
           $table,
           $alias,
           $alias,
           $id_column,
           $alias,
           $ngram);
       }
     }
 
     return $joins;
   }
 
 
   protected function buildNgramsWhereClause(AphrontDatabaseConnection $conn) {
     $where = array();
 
     foreach ($this->ngrams as $ngram) {
       $index = $ngram['index'];
       $value = $ngram['value'];
 
       $column = $index->getColumnName();
       $alias = $this->getPrimaryTableAlias();
       if ($alias) {
         $column = qsprintf($conn, '%T.%T', $alias, $column);
       } else {
         $column = qsprintf($conn, '%T', $column);
       }
 
       $tokens = $index->tokenizeString($value);
       foreach ($tokens as $token) {
         $where[] = qsprintf(
           $conn,
           '%Q LIKE %~',
           $column,
           $token);
       }
     }
 
     return $where;
   }
 
 
   protected function shouldGroupNgramResultRows() {
     return (bool)$this->ngrams;
   }
 
 
 /* -(  Edge Logic  )--------------------------------------------------------- */
 
 
   /**
    * Convenience method for specifying edge logic constraints with a list of
    * PHIDs.
    *
    * @param const Edge constant.
    * @param const Constraint operator.
    * @param list<phid> List of PHIDs.
    * @return this
    * @task edgelogic
    */
   public function withEdgeLogicPHIDs($edge_type, $operator, array $phids) {
     $constraints = array();
     foreach ($phids as $phid) {
       $constraints[] = new PhabricatorQueryConstraint($operator, $phid);
     }
 
     return $this->withEdgeLogicConstraints($edge_type, $constraints);
   }
 
 
   /**
    * @return this
    * @task edgelogic
    */
   public function withEdgeLogicConstraints($edge_type, array $constraints) {
     assert_instances_of($constraints, 'PhabricatorQueryConstraint');
 
     $constraints = mgroup($constraints, 'getOperator');
     foreach ($constraints as $operator => $list) {
       foreach ($list as $item) {
         $this->edgeLogicConstraints[$edge_type][$operator][] = $item;
       }
     }
 
     $this->edgeLogicConstraintsAreValid = false;
 
     return $this;
   }
 
 
   /**
    * @task edgelogic
    */
   public function buildEdgeLogicSelectClause(AphrontDatabaseConnection $conn) {
     $select = array();
 
     $this->validateEdgeLogicConstraints();
 
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
       foreach ($constraints as $operator => $list) {
         $alias = $this->getEdgeLogicTableAlias($operator, $type);
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_AND:
             if (count($list) > 1) {
               $select[] = qsprintf(
                 $conn,
                 'COUNT(DISTINCT(%T.dst)) %T',
                 $alias,
                 $this->buildEdgeLogicTableAliasCount($alias));
             }
             break;
           case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
             // This is tricky. We have a query which specifies multiple
             // projects, each of which may have an arbitrarily large number
             // of descendants.
 
             // Suppose the projects are "Engineering" and "Operations", and
             // "Engineering" has subprojects X, Y and Z.
 
             // We first use `FIELD(dst, X, Y, Z)` to produce a 0 if a row
             // is not part of Engineering at all, or some number other than
             // 0 if it is.
 
             // Then we use `IF(..., idx, NULL)` to convert the 0 to a NULL and
             // any other value to an index (say, 1) for the ancestor.
 
             // We build these up for every ancestor, then use `COALESCE(...)`
             // to select the non-null one, giving us an ancestor which this
             // row is a member of.
 
             // From there, we use `COUNT(DISTINCT(...))` to make sure that
             // each result row is a member of all ancestors.
             if (count($list) > 1) {
               $idx = 1;
               $parts = array();
               foreach ($list as $constraint) {
                 $parts[] = qsprintf(
                   $conn,
                   'IF(FIELD(%T.dst, %Ls) != 0, %d, NULL)',
                   $alias,
                   (array)$constraint->getValue(),
                   $idx++);
               }
               $parts = implode(', ', $parts);
 
               $select[] = qsprintf(
                 $conn,
                 'COUNT(DISTINCT(COALESCE(%Q))) %T',
                 $parts,
                 $this->buildEdgeLogicTableAliasAncestor($alias));
             }
             break;
           default:
             break;
         }
       }
     }
 
     return $select;
   }
 
 
   /**
    * @task edgelogic
    */
   public function buildEdgeLogicJoinClause(AphrontDatabaseConnection $conn) {
     $edge_table = PhabricatorEdgeConfig::TABLE_NAME_EDGE;
     $phid_column = $this->getApplicationSearchObjectPHIDColumn();
 
     $joins = array();
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
 
       $op_null = PhabricatorQueryConstraint::OPERATOR_NULL;
       $has_null = isset($constraints[$op_null]);
 
       foreach ($constraints as $operator => $list) {
         $alias = $this->getEdgeLogicTableAlias($operator, $type);
 
         $phids = array();
         foreach ($list as $constraint) {
           $value = (array)$constraint->getValue();
           foreach ($value as $v) {
             $phids[$v] = $v;
           }
         }
         $phids = array_keys($phids);
 
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_NOT:
             $joins[] = qsprintf(
               $conn,
               'LEFT JOIN %T %T ON %Q = %T.src AND %T.type = %d
                 AND %T.dst IN (%Ls)',
               $edge_table,
               $alias,
               $phid_column,
               $alias,
               $alias,
               $type,
               $alias,
               $phids);
             break;
           case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
           case PhabricatorQueryConstraint::OPERATOR_AND:
           case PhabricatorQueryConstraint::OPERATOR_OR:
             // If we're including results with no matches, we have to degrade
             // this to a LEFT join. We'll use WHERE to select matching rows
             // later.
             if ($has_null) {
               $join_type = 'LEFT';
             } else {
               $join_type = '';
             }
 
             $joins[] = qsprintf(
               $conn,
               '%Q JOIN %T %T ON %Q = %T.src AND %T.type = %d
                 AND %T.dst IN (%Ls)',
               $join_type,
               $edge_table,
               $alias,
               $phid_column,
               $alias,
               $alias,
               $type,
               $alias,
               $phids);
             break;
           case PhabricatorQueryConstraint::OPERATOR_NULL:
             $joins[] = qsprintf(
               $conn,
               'LEFT JOIN %T %T ON %Q = %T.src AND %T.type = %d',
               $edge_table,
               $alias,
               $phid_column,
               $alias,
               $alias,
               $type);
             break;
         }
       }
     }
 
     return $joins;
   }
 
 
   /**
    * @task edgelogic
    */
   public function buildEdgeLogicWhereClause(AphrontDatabaseConnection $conn) {
     $where = array();
 
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
 
       $full = array();
       $null = array();
 
       $op_null = PhabricatorQueryConstraint::OPERATOR_NULL;
       $has_null = isset($constraints[$op_null]);
 
       foreach ($constraints as $operator => $list) {
         $alias = $this->getEdgeLogicTableAlias($operator, $type);
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_NOT:
             $full[] = qsprintf(
               $conn,
               '%T.dst IS NULL',
               $alias);
             break;
           case PhabricatorQueryConstraint::OPERATOR_AND:
           case PhabricatorQueryConstraint::OPERATOR_OR:
             if ($has_null) {
               $full[] = qsprintf(
                 $conn,
                 '%T.dst IS NOT NULL',
                 $alias);
             }
             break;
           case PhabricatorQueryConstraint::OPERATOR_NULL:
             $null[] = qsprintf(
               $conn,
               '%T.dst IS NULL',
               $alias);
             break;
         }
       }
 
       if ($full && $null) {
         $full = $this->formatWhereSubclause($full);
         $null = $this->formatWhereSubclause($null);
         $where[] = qsprintf($conn, '(%Q OR %Q)', $full, $null);
       } else if ($full) {
         foreach ($full as $condition) {
           $where[] = $condition;
         }
       } else if ($null) {
         foreach ($null as $condition) {
           $where[] = $condition;
         }
       }
     }
 
     return $where;
   }
 
 
   /**
    * @task edgelogic
    */
   public function buildEdgeLogicHavingClause(AphrontDatabaseConnection $conn) {
     $having = array();
 
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
       foreach ($constraints as $operator => $list) {
         $alias = $this->getEdgeLogicTableAlias($operator, $type);
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_AND:
             if (count($list) > 1) {
               $having[] = qsprintf(
                 $conn,
                 '%T = %d',
                 $this->buildEdgeLogicTableAliasCount($alias),
                 count($list));
             }
             break;
           case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
             if (count($list) > 1) {
               $having[] = qsprintf(
                 $conn,
                 '%T = %d',
                 $this->buildEdgeLogicTableAliasAncestor($alias),
                 count($list));
             }
             break;
         }
       }
     }
 
     return $having;
   }
 
 
   /**
    * @task edgelogic
    */
   public function shouldGroupEdgeLogicResultRows() {
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
       foreach ($constraints as $operator => $list) {
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_NOT:
           case PhabricatorQueryConstraint::OPERATOR_AND:
           case PhabricatorQueryConstraint::OPERATOR_OR:
             if (count($list) > 1) {
               return true;
             }
             break;
           case PhabricatorQueryConstraint::OPERATOR_ANCESTOR:
             // NOTE: We must always group query results rows when using an
             // "ANCESTOR" operator because a single task may be related to
             // two different descendants of a particular ancestor. For
             // discussion, see T12753.
             return true;
           case PhabricatorQueryConstraint::OPERATOR_NULL:
             return true;
         }
       }
     }
 
     return false;
   }
 
 
   /**
    * @task edgelogic
    */
   private function getEdgeLogicTableAlias($operator, $type) {
     return 'edgelogic_'.$operator.'_'.$type;
   }
 
 
   /**
    * @task edgelogic
    */
   private function buildEdgeLogicTableAliasCount($alias) {
     return $alias.'_count';
   }
 
   /**
    * @task edgelogic
    */
   private function buildEdgeLogicTableAliasAncestor($alias) {
     return $alias.'_ancestor';
   }
 
 
   /**
    * Select certain edge logic constraint values.
    *
    * @task edgelogic
    */
   protected function getEdgeLogicValues(
     array $edge_types,
     array $operators) {
 
     $values = array();
 
     $constraint_lists = $this->edgeLogicConstraints;
     if ($edge_types) {
       $constraint_lists = array_select_keys($constraint_lists, $edge_types);
     }
 
     foreach ($constraint_lists as $type => $constraints) {
       if ($operators) {
         $constraints = array_select_keys($constraints, $operators);
       }
       foreach ($constraints as $operator => $list) {
         foreach ($list as $constraint) {
           $value = (array)$constraint->getValue();
           foreach ($value as $v) {
             $values[] = $v;
           }
         }
       }
     }
 
     return $values;
   }
 
 
   /**
    * Validate edge logic constraints for the query.
    *
    * @return this
    * @task edgelogic
    */
   private function validateEdgeLogicConstraints() {
     if ($this->edgeLogicConstraintsAreValid) {
       return $this;
     }
 
     foreach ($this->edgeLogicConstraints as $type => $constraints) {
       foreach ($constraints as $operator => $list) {
         switch ($operator) {
           case PhabricatorQueryConstraint::OPERATOR_EMPTY:
             throw new PhabricatorEmptyQueryException(
               pht('This query specifies an empty constraint.'));
         }
       }
     }
 
     // This should probably be more modular, eventually, but we only do
     // project-based edge logic today.
 
     $project_phids = $this->getEdgeLogicValues(
       array(
         PhabricatorProjectObjectHasProjectEdgeType::EDGECONST,
       ),
       array(
         PhabricatorQueryConstraint::OPERATOR_AND,
         PhabricatorQueryConstraint::OPERATOR_OR,
         PhabricatorQueryConstraint::OPERATOR_NOT,
         PhabricatorQueryConstraint::OPERATOR_ANCESTOR,
       ));
     if ($project_phids) {
       $projects = id(new PhabricatorProjectQuery())
         ->setViewer($this->getViewer())
         ->setParentQuery($this)
         ->withPHIDs($project_phids)
         ->execute();
       $projects = mpull($projects, null, 'getPHID');
       foreach ($project_phids as $phid) {
         if (empty($projects[$phid])) {
           throw new PhabricatorEmptyQueryException(
             pht(
               'This query is constrained by a project you do not have '.
               'permission to see.'));
         }
       }
     }
 
     $this->edgeLogicConstraintsAreValid = true;
 
     return $this;
   }
 
 
 /* -(  Spaces  )------------------------------------------------------------- */
 
 
   /**
    * Constrain the query to return results from only specific Spaces.
    *
    * Pass a list of Space PHIDs, or `null` to represent the default space. Only
    * results in those Spaces will be returned.
    *
    * Queries are always constrained to include only results from spaces the
    * viewer has access to.
    *
    * @param list<phid|null>
    * @task spaces
    */
   public function withSpacePHIDs(array $space_phids) {
     $object = $this->newResultObject();
 
     if (!$object) {
       throw new Exception(
         pht(
           'This query (of class "%s") does not implement newResultObject(), '.
           'but must implement this method to enable support for Spaces.',
           get_class($this)));
     }
 
     if (!($object instanceof PhabricatorSpacesInterface)) {
       throw new Exception(
         pht(
           'This query (of class "%s") returned an object of class "%s" from '.
           'getNewResultObject(), but it does not implement the required '.
           'interface ("%s"). Objects must implement this interface to enable '.
           'Spaces support.',
           get_class($this),
           get_class($object),
           'PhabricatorSpacesInterface'));
     }
 
     $this->spacePHIDs = $space_phids;
 
     return $this;
   }
 
   public function withSpaceIsArchived($archived) {
     $this->spaceIsArchived = $archived;
     return $this;
   }
 
 
   /**
    * Constrain the query to include only results in valid Spaces.
    *
    * This method builds part of a WHERE clause which considers the spaces the
    * viewer has access to see with any explicit constraint on spaces added by
    * @{method:withSpacePHIDs}.
    *
    * @param AphrontDatabaseConnection Database connection.
    * @return string Part of a WHERE clause.
    * @task spaces
    */
   private function buildSpacesWhereClause(AphrontDatabaseConnection $conn) {
     $object = $this->newResultObject();
     if (!$object) {
       return null;
     }
 
     if (!($object instanceof PhabricatorSpacesInterface)) {
       return null;
     }
 
     $viewer = $this->getViewer();
 
     // If we have an omnipotent viewer and no formal space constraints, don't
     // emit a clause. This primarily enables older migrations to run cleanly,
     // without fataling because they try to match a `spacePHID` column which
     // does not exist yet. See T8743, T8746.
     if ($viewer->isOmnipotent()) {
       if ($this->spaceIsArchived === null && $this->spacePHIDs === null) {
         return null;
       }
     }
 
     $space_phids = array();
     $include_null = false;
 
     $all = PhabricatorSpacesNamespaceQuery::getAllSpaces();
     if (!$all) {
       // If there are no spaces at all, implicitly give the viewer access to
       // the default space.
       $include_null = true;
     } else {
       // Otherwise, give them access to the spaces they have permission to
       // see.
       $viewer_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpaces(
         $viewer);
       foreach ($viewer_spaces as $viewer_space) {
         if ($this->spaceIsArchived !== null) {
           if ($viewer_space->getIsArchived() != $this->spaceIsArchived) {
             continue;
           }
         }
         $phid = $viewer_space->getPHID();
         $space_phids[$phid] = $phid;
         if ($viewer_space->getIsDefaultNamespace()) {
           $include_null = true;
         }
       }
     }
 
     // If we have additional explicit constraints, evaluate them now.
     if ($this->spacePHIDs !== null) {
       $explicit = array();
       $explicit_null = false;
       foreach ($this->spacePHIDs as $phid) {
         if ($phid === null) {
           $space = PhabricatorSpacesNamespaceQuery::getDefaultSpace();
         } else {
           $space = idx($all, $phid);
         }
 
         if ($space) {
           $phid = $space->getPHID();
           $explicit[$phid] = $phid;
           if ($space->getIsDefaultNamespace()) {
             $explicit_null = true;
           }
         }
       }
 
       // If the viewer can see the default space but it isn't on the explicit
       // list of spaces to query, don't match it.
       if ($include_null && !$explicit_null) {
         $include_null = false;
       }
 
       // Include only the spaces common to the viewer and the constraints.
       $space_phids = array_intersect_key($space_phids, $explicit);
     }
 
     if (!$space_phids && !$include_null) {
       if ($this->spacePHIDs === null) {
         throw new PhabricatorEmptyQueryException(
           pht('You do not have access to any spaces.'));
       } else {
         throw new PhabricatorEmptyQueryException(
           pht(
             'You do not have access to any of the spaces this query '.
             'is constrained to.'));
       }
     }
 
     $alias = $this->getPrimaryTableAlias();
     if ($alias) {
       $col = qsprintf($conn, '%T.spacePHID', $alias);
     } else {
       $col = 'spacePHID';
     }
 
     if ($space_phids && $include_null) {
       return qsprintf(
         $conn,
         '(%Q IN (%Ls) OR %Q IS NULL)',
         $col,
         $space_phids,
         $col);
     } else if ($space_phids) {
       return qsprintf(
         $conn,
         '%Q IN (%Ls)',
         $col,
         $space_phids);
     } else {
       return qsprintf(
         $conn,
         '%Q IS NULL',
         $col);
     }
   }
 
 }