owners-client: Add support for excluding owners.

It is useful to exclude the change author when suggesting owners.

Change-Id: I3321c013271f6cea1098abba59b509800818917e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2669680
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>

owners_client.py

@@ -104,12 +104,15 @@ class OwnersClient(object):
         status[path] = self.INSUFFICIENT_REVIEWERS
     return status
 
-  def ScoreOwners(self, paths):
+  def ScoreOwners(self, paths, exclude=None):
     """Get sorted list of owners for the given paths."""
+    exclude = exclude or []
     positions_by_owner = {}
     owners_by_path = self.BatchListOwners(paths)
     for owners in owners_by_path.values():
       for i, owner in enumerate(owners):
+        if owner in exclude:
+          continue
         # Gerrit API lists owners of a path sorted by an internal score, so
         # owners that appear first should be prefered.
         # We define the score of an owner based on the pair
@@ -124,22 +127,26 @@ class OwnersClient(object):
         key=lambda o: (-len(positions_by_owner[o]),
                        min(positions_by_owner[o]) + random.random()))
 
-  def SuggestOwners(self, paths):
+  def SuggestOwners(self, paths, exclude=None):
     """Suggest a set of owners for the given paths."""
+    exclude = exclude or []
     paths_by_owner = {}
     owners_by_path = self.BatchListOwners(paths)
     for path, owners in owners_by_path.items():
       for owner in owners:
-        paths_by_owner.setdefault(owner, set()).add(path)
+        if owner not in exclude:
+          paths_by_owner.setdefault(owner, set()).add(path)
 
     # Select the minimum number of owners that can approve all paths.
     # We start at 2 to avoid sending all changes that require multiple
     # reviewers to top-level owners.
-    owners = self.ScoreOwners(paths)
+    owners = self.ScoreOwners(paths, exclude=exclude)
     if len(owners) < 2:
       return owners
 
-    for num_owners in range(2, len(owners)):
+    # Note that we have to iterate up to len(owners) + 1.
+    # e.g. if there are only 2 owners, we should consider num_owners = 2.
+    for num_owners in range(2, len(owners) + 1):
       # Iterate all combinations of `num_owners` by decreasing score, and
       # select the first one that covers all paths.
       for selected in _owner_combinations(owners, num_owners):
@@ -147,6 +154,8 @@ class OwnersClient(object):
         if len(covered) == len(paths):
           return list(selected)
 
+    return []
+
 
 class DepotToolsClient(OwnersClient):
   """Implement OwnersClient using owners.py Database."""

tests/owners_client_test.py

@@ -165,6 +165,17 @@ class OwnersClientTest(unittest.TestCase):
       [bob, alice, chris]
     )
 
+    self.client.owners_by_path = {
+        'a': [alice, bob],
+        'b': [bob],
+        'c': [bob, chris]
+    }
+    self.assertEqual(
+      self.client.ScoreOwners(
+          self.client.owners_by_path.keys(), exclude=[chris]),
+      [bob, alice],
+    )
+
     self.client.owners_by_path = {
         'a': [alice, bob, chris, dave],
         'b': [chris, bob, dave],
@@ -187,6 +198,11 @@ class OwnersClientTest(unittest.TestCase):
         sorted(self.client.SuggestOwners(['abcd'])),
         [alice, bob])
 
+    self.client.owners_by_path = {'abcd': [alice, bob, chris, dave]}
+    self.assertEqual(
+        sorted(self.client.SuggestOwners(['abcd'], exclude=[alice, bob])),
+        [chris, dave])
+
     self.client.owners_by_path = {
         'ae': [alice, emily],
         'be': [bob, emily],