Combine the two different ngram-splitting algorithms into a single engine

Summary:
Ref T13501. Depends on D21127. With the "prefix" behavior removed in D21127, we now have two virtually identical copies of the same code.

The newer one in Ferret is better: it slices utf8 correctly and is slightly more efficient on large inputs. Pull it out and make all callers call into it.

Test Plan:
- Grepped for all affected symbols.
- Ran `bin/search index --force ...` to reindex various objects (tasks, files).
- Searched for things in the UI.

Maniphest Tasks: T13501

Differential Revision: https://secure.phabricator.com/D21128

src/__phutil_library_map__.php

···
     'PhabricatorSearchManagementNgramsWorkflow' => 'applications/search/management/PhabricatorSearchManagementNgramsWorkflow.php',
     'PhabricatorSearchManagementQueryWorkflow' => 'applications/search/management/PhabricatorSearchManagementQueryWorkflow.php',
     'PhabricatorSearchManagementWorkflow' => 'applications/search/management/PhabricatorSearchManagementWorkflow.php',
+    'PhabricatorSearchNgramEngine' => 'applications/search/engine/PhabricatorSearchNgramEngine.php',
     'PhabricatorSearchNgrams' => 'applications/search/ngrams/PhabricatorSearchNgrams.php',
     'PhabricatorSearchNgramsDestructionEngineExtension' => 'applications/search/engineextension/PhabricatorSearchNgramsDestructionEngineExtension.php',
     'PhabricatorSearchOrderController' => 'applications/search/controller/PhabricatorSearchOrderController.php',
···
     'PhabricatorSearchManagementNgramsWorkflow' => 'PhabricatorSearchManagementWorkflow',
     'PhabricatorSearchManagementQueryWorkflow' => 'PhabricatorSearchManagementWorkflow',
     'PhabricatorSearchManagementWorkflow' => 'PhabricatorManagementWorkflow',
+    'PhabricatorSearchNgramEngine' => 'Phobject',
     'PhabricatorSearchNgrams' => 'PhabricatorSearchDAO',
     'PhabricatorSearchNgramsDestructionEngineExtension' => 'PhabricatorDestructionEngineExtension',
     'PhabricatorSearchOrderController' => 'PhabricatorSearchBaseController',

src/applications/search/engine/PhabricatorSearchNgramEngine.php

···
+<?php
+
+final class PhabricatorSearchNgramEngine
+  extends Phobject {
+
+  public function tokenizeNgramString($value) {
+    $value = trim($value, ' ');
+    $value = preg_split('/\s+/u', $value);
+    return $value;
+  }
+
+  public function getTermNgramsFromString($string) {
+    return $this->getNgramsFromString($string, true);
+  }
+
+  public function getSubstringNgramsFromString($string) {
+    return $this->getNgramsFromString($string, false);
+  }
+
+  private function getNgramsFromString($value, $as_term) {
+    $value = phutil_utf8_strtolower($value);
+    $tokens = $this->tokenizeNgramString($value);
+
+    // First, extract unique tokens from the string. This reduces the number
+    // of `phutil_utf8v()` calls we need to make if we are indexing a large
+    // corpus with redundant terms.
+    $unique_tokens = array();
+    foreach ($tokens as $token) {
+      if ($as_term) {
+        $token = ' '.$token.' ';
+      }
+
+      $unique_tokens[$token] = true;
+    }
+
+    $ngrams = array();
+    foreach ($unique_tokens as $token => $ignored) {
+      $token_v = phutil_utf8v($token);
+      $length = count($token_v);
+
+      // NOTE: We're being somewhat clever here to micro-optimize performance,
+      // especially for very long strings. See PHI87.
+
+      $token_l = array();
+      for ($ii = 0; $ii < $length; $ii++) {
+        $token_l[$ii] = strlen($token_v[$ii]);
+      }
+
+      $ngram_count = $length - 2;
+      $cursor = 0;
+      for ($ii = 0; $ii < $ngram_count; $ii++) {
+        $ngram_l = $token_l[$ii] + $token_l[$ii + 1] + $token_l[$ii + 2];
+
+        $ngram = substr($token, $cursor, $ngram_l);
+        $ngrams[$ngram] = $ngram;
+
+        $cursor += $token_l[$ii];
+      }
+    }
+
+    ksort($ngrams);
+
+    return array_keys($ngrams);
+  }
+
+}

src/applications/search/engineextension/PhabricatorFerretFulltextEngineExtension.php

···
     }
     $ngrams_source = implode("\n", $ngrams_source);
 
-    $ngrams = $engine->getTermNgramsFromString($ngrams_source);
+    $ngram_engine = new PhabricatorSearchNgramEngine();
+    $ngrams = $ngram_engine->getTermNgramsFromString($ngrams_source);
 
     $object->openTransaction();
 

src/applications/search/ferret/PhabricatorFerretEngine.php

···
     return new PhutilSearchStemmer();
   }
 
-  public function tokenizeString($value) {
-    $value = trim($value, ' ');
-    $value = preg_split('/\s+/u', $value);
-    return $value;
-  }
-
-  public function getTermNgramsFromString($string) {
-    return $this->getNgramsFromString($string, true);
-  }
-
-  public function getSubstringNgramsFromString($string) {
-    return $this->getNgramsFromString($string, false);
-  }
-
-  private function getNgramsFromString($value, $as_term) {
-    $value = phutil_utf8_strtolower($value);
-    $tokens = $this->tokenizeString($value);
-
-    // First, extract unique tokens from the string. This reduces the number
-    // of `phutil_utf8v()` calls we need to make if we are indexing a large
-    // corpus with redundant terms.
-    $unique_tokens = array();
-    foreach ($tokens as $token) {
-      if ($as_term) {
-        $token = ' '.$token.' ';
-      }
-
-      $unique_tokens[$token] = true;
-    }
-
-    $ngrams = array();
-    foreach ($unique_tokens as $token => $ignored) {
-      $token_v = phutil_utf8v($token);
-      $length = count($token_v);
-
-      // NOTE: We're being somewhat clever here to micro-optimize performance,
-      // especially for very long strings. See PHI87.
-
-      $token_l = array();
-      for ($ii = 0; $ii < $length; $ii++) {
-        $token_l[$ii] = strlen($token_v[$ii]);
-      }
-
-      $ngram_count = $length - 2;
-      $cursor = 0;
-      for ($ii = 0; $ii < $ngram_count; $ii++) {
-        $ngram_l = $token_l[$ii] + $token_l[$ii + 1] + $token_l[$ii + 2];
-
-        $ngram = substr($token, $cursor, $ngram_l);
-        $ngrams[$ngram] = $ngram;
-
-        $cursor += $token_l[$ii];
-      }
-    }
-
-    ksort($ngrams);
-
-    return array_keys($ngrams);
-  }
-
   public function newTermsCorpus($raw_corpus) {
     $term_corpus = strtr(
       $raw_corpus,

src/applications/search/ferret/__tests__/PhabricatorFerretEngineTestCase.php

···
       ),
     );
 
-    $engine = new ManiphestTaskFerretEngine();
+    $ngram_engine = new PhabricatorSearchNgramEngine();
 
     foreach ($map as $input => $expect) {
-      $actual = $engine->getTermNgramsFromString($input);
+      $actual = $ngram_engine->getTermNgramsFromString($input);
       $this->assertEqual(
         $actual,
         $expect,

src/applications/search/ngrams/PhabricatorSearchNgrams.php

···
   protected $ngram;
 
   private $value;
+  private $ngramEngine;
 
   abstract public function getNgramKey();
   abstract public function getColumnName();
···
     return "{$application}_{$key}_ngrams";
   }
 
-  final public function tokenizeString($value) {
-    $value = trim($value, ' ');
-    $value = preg_split('/ +/', $value);
-    return $value;
-  }
-
-  final public function getNgramsFromString($value, $mode) {
-    $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;
-      }
-
-      $len = (strlen($token) - 2);
-      for ($ii = 0; $ii < $len; $ii++) {
-        $ngram = substr($token, $ii, 3);
-        $ngrams[$ngram] = $ngram;
-      }
-    }
+  final public function writeNgram($object_id) {
+    $ngram_engine = $this->getNgramEngine();
+    $ngrams = $ngram_engine->getTermNgramsFromString($this->getValue());
 
-    ksort($ngrams);
-
-    return array_keys($ngrams);
-  }
-
-  final public function writeNgram($object_id) {
-    $ngrams = $this->getNgramsFromString($this->getValue(), 'index');
     $conn_w = $this->establishConnection('w');
 
     $sql = array();
···
     }
 
     return $this;
+  }
+
+  private function getNgramEngine() {
+    if (!$this->ngramEngine) {
+      $this->ngramEngine = new PhabricatorSearchNgramEngine();
+    }
+
+    return $this->ngramEngine;
   }
 
 }

src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php

···
   private $ferretTables = array();
   private $ferretQuery;
   private $ferretMetadata = array();
+  private $ngramEngine;
 
   const FULLTEXT_RANK = '_ft_rank';
   const FULLTEXT_MODIFIED = '_ft_epochModified';
···
     $stemmer = $engine->newStemmer();
 
     $ngram_table = $engine->getNgramsTableName();
+    $ngram_engine = $this->getNgramEngine();
 
     $flat = array();
     foreach ($this->ferretTokens as $fulltext_token) {
···
       }
 
       if ($is_substring) {
-        $ngrams = $engine->getSubstringNgramsFromString($value);
+        $ngrams = $ngram_engine->getSubstringNgramsFromString($value);
       } else {
         $terms_value = $engine->newTermsCorpus($value);
-        $ngrams = $engine->getTermNgramsFromString($terms_value);
+        $ngrams = $ngram_engine->getTermNgramsFromString($terms_value);
 
         // If this is a stemmed term, only look for ngrams present in both the
         // unstemmed and stemmed variations.
···
           // is (or, at least, may be) a normal word and activates.
           $terms_value = trim($terms_value, ' ');
           $stem_value = $stemmer->stemToken($terms_value);
-          $stem_ngrams = $engine->getTermNgramsFromString($stem_value);
+          $stem_ngrams = $ngram_engine->getTermNgramsFromString($stem_value);
           $ngrams = array_intersect($ngrams, $stem_ngrams);
         }
       }
···
 
 
   protected function buildNgramsJoinClause(AphrontDatabaseConnection $conn) {
+    $ngram_engine = $this->getNgramEngine();
+
     $flat = array();
     foreach ($this->ngrams as $spec) {
       $length = $spec['length'];
···
       $index = $spec['index'];
       $value = $spec['value'];
 
-      $ngrams = $index->getNgramsFromString($value, 'query');
+      $ngrams = $ngram_engine->getSubstringNgramsFromString($value);
 
       foreach ($ngrams as $ngram) {
         $flat[] = array(
···
   protected function buildNgramsWhereClause(AphrontDatabaseConnection $conn) {
     $where = array();
 
+    $ngram_engine = $this->getNgramEngine();
+
     foreach ($this->ngrams as $ngram) {
       $index = $ngram['index'];
       $value = $ngram['value'];
···
         $column = qsprintf($conn, '%T', $column);
       }
 
-      $tokens = $index->tokenizeString($value);
+      $tokens = $ngram_engine->tokenizeNgramString($value);
+
       foreach ($tokens as $token) {
         $where[] = qsprintf(
           $conn,
···
 
   protected function shouldGroupNgramResultRows() {
     return (bool)$this->ngrams;
+  }
+
+  private function getNgramEngine() {
+    if (!$this->ngramEngine) {
+      $this->ngramEngine = new PhabricatorSearchNgramEngine();
+    }
+
+    return $this->ngramEngine;
   }