Presubmit: Fix relative owners check

This ensures relative file: directives in OWNERS files also work if
the directory of the owners file gets deleted.

Bug: 1015444
Change-Id: I9471a28a7246513120dd3ebb924f6d64eb50c2df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1870249Reviewed-by: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>

owners.py

@@ -441,7 +441,7 @@ class Database(object):
     else:
       assert start.startswith(self.root)
       start = self.os_path.dirname(self.os_path.relpath(start, self.root))
-      include_path = self.os_path.join(start, path)
+      include_path = self.os_path.normpath(self.os_path.join(start, path))
 
     if include_path in self.override_files:
       return include_path

testing_support/filesystem_mock.py

@@ -77,6 +77,19 @@ class MockFileSystem(object):
   def open_for_reading(self, path):
     return StringIO.StringIO(self.read_binary_file(path))
 
+  def normpath(self, path):
+    # This is not a complete implementation of normpath. Only covers what we
+    # use in tests.
+    result = []
+    for part in path.split(self.sep):
+      if part == '..':
+        result.pop()
+      elif part == '.':
+        continue
+      else:
+        result.append(part)
+    return self.sep.join(result)
+
   def read_binary_file(self, path):
     # Intentionally raises KeyError if we don't recognize the path.
     if self.files[path] is None:

tests/owners_unittest.py

@@ -52,6 +52,7 @@ def test_repo():
     '/chrome/renderer/OWNERS': owners_file(peter),
     '/chrome/renderer/gpu/gpu_channel_host.h': '',
     '/chrome/renderer/safe_browsing/scorer.h': '',
+    '/chrome/tools/OWNERS': owners_file(file='../OWNERS'),
     '/content/OWNERS': owners_file(john, darin, comment='foo', noparent=True),
     '/content/comment/OWNERS': owners_file(john + '  # for comments',
                                            darin + '  # for everything else'),
@@ -415,6 +416,10 @@ class ReviewersForTest(_BaseTestCase):
                               [[john],
                                [darin]])
 
+  def test_reviewers_for__relative_owners_file(self):
+    self.assert_reviewers_for(['chrome/tools/OWNERS'],
+                              [[ben], [brett]])
+
   def test_reviewers_for__valid_inputs(self):
     db = self.db()