Fix CheckForCommitObjects to check missing gitlink changes

https://crrev.com/c/7234371 made some optimizations to the check
but caused it to start missing changes that modified DEPS but not
the corresponding gitlink.

Fix the check by doing a full tree scan when DEPS is updated.

Bug: 469784282
Change-Id: Ibdcdcb1af5a330e4d9e96daecd28e06bc1436022
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/7362007
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Josiah Kiehl <kiehl@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

presubmit_canned_checks.py

@@ -2081,8 +2081,13 @@ def CheckForCommitObjects(input_api, output_api):
     # If the number of affected files is small, we can avoid scanning the entire
     # tree.
     affected_files = list(input_api.AffectedFiles())
+
+    # We must scan the full tree if DEPS is modified to ensure that any change
+    # in DEPS is reflected in the gitlinks.
+    deps_modified = any(f.LocalPath() == 'DEPS' for f in affected_files)
+
     cmd = ['git', 'ls-tree', '-z', '--full-tree', 'HEAD']
-    if len(affected_files) < 1000:
+    if len(affected_files) < 1000 and not deps_modified:
         # We need to pass the paths relative to the repository root.
         repo_root = input_api.change.RepositoryRoot()
         files_to_check = [

tests/check_for_commit_objects_test.py

@@ -14,6 +14,18 @@ import presubmit_canned_checks
 from testing_support.presubmit_canned_checks_test_mocks import MockInputApi, MockOutputApi, MockFile
 
 
+class MockRelativeFile(MockFile):
+
+    def __init__(self, rel_path, new_contents):
+        # We pass absolute path to super so AbsoluteLocalPath returns absolute path
+        abs_path = os.path.join('/tmp/repo', rel_path)
+        super(MockRelativeFile, self).__init__(abs_path, new_contents)
+        self._rel_path = rel_path
+
+    def LocalPath(self):
+        return self._rel_path
+
+
 class CheckForCommitObjectsTest(unittest.TestCase):
 
     def setUp(self):
@@ -70,6 +82,24 @@ class CheckForCommitObjectsTest(unittest.TestCase):
         self.assertIn('--full-tree', args)
         self.assertNotIn('f0.txt', args)
 
+    def testFullTreeExecutionWhenDepsModified(self):
+        # Small CL but DEPS is modified, should run full tree scan
+        self.input_api.files = [
+            MockRelativeFile('DEPS', []),
+            MockRelativeFile('other.txt', [])
+        ]
+
+        self.input_api.subprocess.check_output = mock.Mock(return_value=b'')
+
+        presubmit_canned_checks.CheckForCommitObjects(self.input_api,
+                                                      self.output_api)
+
+        args = self.input_api.subprocess.check_output.call_args[0][0]
+        self.assertIn('ls-tree', args)
+        self.assertIn('--full-tree', args)
+        # Should not list specific files when running full tree
+        self.assertNotIn('other.txt', args)
+
     def testBatchedFoundCommit(self):
         # 1 file, found a commit object (gitlink)
         self.input_api.files = [