Add option to enable Lucene 8 index compatibility (#1953)

Addresses #1952 - add a flag -lucene8 that abandons consistent tie breaking,
so retrieval doesn't need to touch the docvalues. In the regression script, a 
similar option --lucene8 allows the score matching to be more lenient.

src/main/java/io/anserini/search/SearchArgs.java

@@ -36,6 +36,9 @@ public class SearchArgs {
   @Option(name = "-topicreader", required = true, usage = "TopicReader to use.")
   public String topicReader;
 
+  @Option(name = "-lucene8", usage = "Enable Lucene 8 index compatibility.")
+  public Boolean lucene8 = false;
+
   // optional arguments
   @Option(name = "-querygenerator", usage = "QueryGenerator to use.")
   public String queryGenerator = "BagOfWordsQueryGenerator";

src/main/java/io/anserini/search/SearchCollection.java

@@ -494,6 +494,12 @@ public SearchCollection(SearchArgs args) throws IOException {
       loadQrels(args.rf_qrels);      
     }
 
+    // See https://github.com/castorini/anserini/issues/1952
+    // The solution to the issue described above is to turn off deterministic tie-breaking.
+    if (args.lucene8) {
+      args.arbitraryScoreTieBreak = true;
+      args.axiom_deterministic = false;
+    }
   }
 
   @Override

src/main/python/run_regression.py

@@ -61,6 +61,10 @@ def is_close(a, b, rel_tol=1e-09, abs_tol=0.0):
     return abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)
 
 
+def is_close_lucene8(a, b):
+    return abs(a-b) <= 0.001
+
+
 def check_output(command):
     # Python 2.6 compatible subprocess.check_output
     process = Popen(command, shell=True, stdout=PIPE)
@@ -131,6 +135,7 @@ def construct_search_commands(yaml_data):
             '-topicreader', topic_set['topic_reader'] if 'topic_reader' in topic_set and topic_set['topic_reader'] else yaml_data['topic_reader'],
             '-output', construct_runfile_path(yaml_data['corpus'], topic_set['id'], model['name']),
             model['params'],
+            '-lucene8' if args.lucene8 else ''
         ]
         for (model, topic_set) in list(itertools.product(yaml_data['models'], yaml_data['topics']))
     ]
@@ -154,6 +159,7 @@ def construct_convert_commands(yaml_data):
 def evaluate_and_verify(yaml_data, dry_run):
     fail_str = '\033[91m[FAIL]\033[0m '
     ok_str = '   [OK] '
+    okish_str = '  \033[94m[OK*]\033[0m '
     failures = False
 
     logger.info('='*10 + ' Verifying Results: ' + yaml_data['corpus'] + ' ' + '='*10)
@@ -181,8 +187,11 @@ def evaluate_and_verify(yaml_data, dry_run):
                 if is_close(expected, actual):
                     logger.info(ok_str + result_str)
                 else:
-                    logger.error(fail_str + result_str)
-                    failures = True
+                    if args.lucene8 and is_close_lucene8(expected, actual):
+                        logger.info(okish_str + result_str)
+                    else:
+                        logger.error(fail_str + result_str)
+                        failures = True
 
     if not dry_run:
         if failures:
@@ -280,6 +289,7 @@ def download_url(url, save_dir, local_filename=None, md5=None, force=False, verb
                         help='Number of converting runs to execute in parallel.')
     parser.add_argument('--dry-run', dest='dry_run', action='store_true',
                         help='Output commands without actual execution.')
+    parser.add_argument('--lucene8', dest='lucene8', action='store_true', help='Enable Lucene 8 index compatibility.')
     args = parser.parse_args()
 
     with open('src/main/resources/regression/{}.yaml'.format(args.regression)) as f:
@@ -340,6 +350,8 @@ def download_url(url, save_dir, local_filename=None, md5=None, force=False, verb
     # Search and verify results.
     if args.search:
         logger.info('='*10 + ' Ranking ' + '='*10)
+        if args.lucene8:
+            logger.info('Enabling Lucene 8 index compatibility.')
         search_cmds = construct_search_commands(yaml_data)
         if args.dry_run:
             for cmd in search_cmds: