Use stemming in the MySQL fulltext search engine

Summary:
Ref T6740. When we index a document, also save a copy of the stemmed version.

When querying, search the combined corpus for the terms.

(We may need to tune this a bit later since it's possible for literal, quoted terms to match in the stemmed section, but I think this wil rarely cause issues in practice.)

A downside here is that search sort of breaks if you upgrade into this and don't reindex. I wasn't able to find a way to issue the query that remained compatible with older indexes and didn't have awful performance, so my plan is:

  - Put this on `secure`.
  - Rebuild the index.
  - If things look good after a couple of days, add a way that we can tell people they need to rebuild the search index with a setup warning.

We might get some reports between now and then, but if this is super awful we should know by the end of the weekend.

Test Plan:
WOW AMAZING

{F2021466}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T6740

Differential Revision: https://secure.phabricator.com/D16947

resources/sql/autopatches/20161125.search.01.stemmed.sql

@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_search.search_documentfield
+  ADD stemmedCorpus LONGTEXT COLLATE {$COLLATE_FULLTEXT};

src/applications/search/fulltextstorage/PhabricatorMySQLFulltextStorageEngine.php

@@ -33,6 +33,8 @@ final class PhabricatorMySQLFulltextStorageEngine
 
     $conn_w = $store->establishConnection('w');
 
+    $stemmer = new PhutilSearchStemmer();
+
     $field_dao = new PhabricatorSearchDocumentField();
     queryfx(
       $conn_w,
@@ -41,16 +43,21 @@ final class PhabricatorMySQLFulltextStorageEngine
       $phid);
     foreach ($doc->getFieldData() as $field) {
       list($ftype, $corpus, $aux_phid) = $field;
+
+      $stemmed_corpus = $stemmer->stemCorpus($corpus);
+
       queryfx(
         $conn_w,
-        'INSERT INTO %T (phid, phidType, field, auxPHID, corpus) '.
-        'VALUES (%s, %s, %s, %ns, %s)',
+        'INSERT INTO %T
+          (phid, phidType, field, auxPHID, corpus, stemmedCorpus) '.
+        'VALUES (%s, %s, %s, %ns, %s, %s)',
         $field_dao->getTableName(),
         $phid,
         $doc->getDocumentType(),
         $ftype,
         $aux_phid,
-        $corpus);
+        $corpus,
+        $stemmed_corpus);
     }
 
 
@@ -205,8 +212,9 @@ final class PhabricatorMySQLFulltextStorageEngine
     if (strlen($compiled_query)) {
       $select[] = qsprintf(
         $conn,
-        'IF(field.field = %s, %d, 0) + '.
-        'MATCH(corpus) AGAINST (%s IN BOOLEAN MODE) AS fieldScore',
+        'IF(field.field = %s, %d, 0) +
+          MATCH(corpus, stemmedCorpus) AGAINST (%s IN BOOLEAN MODE)
+            AS fieldScore',
         $title_field,
         $title_boost,
         $compiled_query);
@@ -218,7 +226,7 @@ final class PhabricatorMySQLFulltextStorageEngine
 
       $where[] = qsprintf(
         $conn,
-        'MATCH(corpus) AGAINST (%s IN BOOLEAN MODE)',
+        'MATCH(corpus, stemmedCorpus) AGAINST (%s IN BOOLEAN MODE)',
         $compiled_query);
 
       if ($query->getParameter('field')) {
@@ -380,11 +388,17 @@ final class PhabricatorMySQLFulltextStorageEngine
   }
 
   private function compileQuery($raw_query) {
-    $compiler = PhabricatorSearchDocument::newQueryCompiler();
+    $stemmer = new PhutilSearchStemmer();
 
-    return $compiler
+    $compiler = PhabricatorSearchDocument::newQueryCompiler()
       ->setQuery($raw_query)
-      ->compileQuery();
+      ->setStemmer($stemmer);
+
+    $queries = array();
+    $queries[] = $compiler->compileLiteralQuery();
+    $queries[] = $compiler->compileStemmedQuery();
+
+    return implode(' ', array_filter($queries));
   }
 
   public function indexExists() {

src/applications/search/storage/document/PhabricatorSearchDocumentField.php

@@ -6,6 +6,7 @@ final class PhabricatorSearchDocumentField extends PhabricatorSearchDAO {
   protected $field;
   protected $auxPHID;
   protected $corpus;
+  protected $stemmedCorpus;
 
   protected function getConfiguration() {
     return array(
@@ -16,14 +17,15 @@ final class PhabricatorSearchDocumentField extends PhabricatorSearchDAO {
         'field' => 'text4',
         'auxPHID' => 'phid?',
         'corpus' => 'fulltext?',
+        'stemmedCorpus' => 'fulltext?',
       ),
       self::CONFIG_KEY_SCHEMA => array(
         'key_phid' => null,
         'phid' => array(
           'columns' => array('phid'),
         ),
-        'corpus' => array(
-          'columns' => array('corpus'),
+        'key_corpus' => array(
+          'columns' => array('corpus', 'stemmedCorpus'),
           'type' => 'FULLTEXT',
         ),
       ),