[Predator] Fix bug in min_distance after refactor and add back skip added/deleted deps.

appengine/findit/crash/changelist_classifier.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import logging
 from collections import defaultdict
 
 from common import chrome_dependency_fetcher
 from crash import crash_util
 from crash.results import MatchResults
@@ skipping 53 matching lines @@
                   frame_list=stack[:self.top_n_frames])
         for stack in report.stacktrace])
 
     # We are only interested in the deps in crash stack (the callstack that
     # caused the crash).
     # TODO(wrengr): we may want to receive the crash deps as an argument,
     # so that when this method is called via Findit.FindCulprit, we avoid
     # doing redundant work creating it.
     stack_deps = GetDepsInCrashStack(
         report.stacktrace.crash_stack,
-        chrome_dependency_fetcher.ChromeDependencyFetcher(self._repository
-            ).GetDependency(report.crashed_version, report.platform))
+        chrome_dependency_fetcher.ChromeDependencyFetcher(
+            self._repository).GetDependency(report.crashed_version,
+                                            report.platform))
 
     # Get dep and file to changelogs, stack_info and blame dicts.
-    regression_deps_rolls = chrome_dependency_fetcher.ChromeDependencyFetcher(
+    dep_rolls = chrome_dependency_fetcher.ChromeDependencyFetcher(
         self._repository).GetDependencyRollsDict(
             last_good_version, first_bad_version, report.platform)
+
+    # Regression of a dep added/deleted (old_revision/new_revision is None) can
+    # not be known for sure and this case rarely happens, so just filter them
+    # out.
+    regression_deps_rolls = {}
+    for dep_path, dep_roll in dep_rolls.iteritems():
+      if not dep_roll.old_revision or not dep_roll.new_revision:
+        logging.info('Skip %s denpendency %s',
+                     'added' if dep_roll.new_revision else 'deleted', dep_path)
+        continue
+      regression_deps_rolls[dep_path] = dep_roll
+
     dep_to_file_to_changelogs, ignore_cls = GetChangeLogsForFilesGroupedByDeps(
         regression_deps_rolls, stack_deps, self._repository)
     dep_to_file_to_stack_infos = GetStackInfosForFilesGroupedByDeps(
         stacktrace, stack_deps)
 
     # TODO: argument order is inconsistent from others. Repository should
     # be last argument.
     results = FindMatchResults(dep_to_file_to_changelogs,
                                dep_to_file_to_stack_infos,
                                stack_deps, self._repository, ignore_cls)
@@ skipping 93 matching lines @@
     dep_roll = regression_deps_rolls.get(dep)
     if not dep_roll:
       continue
 
     dep_roll = regression_deps_rolls[dep]
 
     repository.repo_url = dep_roll.repo_url
     changelogs = repository.GetChangeLogs(dep_roll.old_revision,
                                           dep_roll.new_revision)
 
+    if not changelogs:
+      continue
+
     for changelog in changelogs:
       # When someone reverts, we need to skip both the CL doing
       # the reverting as well as the CL that got reverted. If
       # ``reverted_revision`` is true, then this CL reverts another one,
       # so we skip it and save the CL it reverts in ``reverted_cls`` to
       # be filtered out later.
       if changelog.reverted_revision:
         reverted_cls.add(changelog.reverted_revision)
         continue
 
@@ skipping 81 matching lines @@
 
         blame = repository.GetBlame(touched_file_path,
                                     stack_deps[dep].revision)
 
         # Generate/update each result(changelog) in changelogs, blame is used
         # to calculate distance between touched lines and crashed lines in file.
         match_results.GenerateMatchResults(
             touched_file_path, dep, stack_infos, changelogs, blame)
 
   return match_results.values()