[histograms/validate_format.py] Allow OWNERS files to have no new OWNERs.

This CL fixes an issue where validate_format.py would catch OWNERS files
that were 'empty' because they only had OWNERS that were already in
the list of <owner> emails.

Bug: 1055668
Change-Id: Ie832a566d3c99cfaaa0ad621def8f990190b5bda
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076639
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745314}

tools/metrics/histograms/expand_owners.py

@@ -229,6 +229,8 @@ def _MakeOwners(document, path, emails_with_dom_elements):
   owner_elements = []
   # TODO(crbug.com/987709): An OWNERS file API would be ideal.
   emails_from_owners_file = _ExtractEmailAddressesFromOWNERS(path)
+  if not emails_from_owners_file:
+    raise Error('No emails could be derived from {}.'.format(path))
 
   # A list is used to respect the order of email addresses in the OWNERS file.
   deduped_emails_from_owners_file = []
@@ -332,7 +334,7 @@ def ExpandHistogramsOWNERS(histograms):
       owners_to_add = _MakeOwners(
         owner.ownerDocument, path, emails_with_dom_elements)
       if not owners_to_add:
-        raise Error('No emails could be derived from {}.'.format(path))
+        continue
 
       _UpdateHistogramOwners(histogram, owner, owners_to_add)
 

tools/metrics/histograms/expand_owners_unittest.py

@@ -295,7 +295,7 @@ class ExpandOwnersTest(unittest.TestCase):
 <histograms>
 
 <histogram name="Caffeination" units="mg">
-  <owner>joe@chormium.org</owner>
+  <owner>joe@chromium.org</owner>
   <owner>src/medium/medium/roast/OWNERS</owner>
   <summary>I like coffee.</summary>
 </histogram>
@@ -320,7 +320,7 @@ class ExpandOwnersTest(unittest.TestCase):
 <histograms>
 
 <histogram name="Caffeination" units="mg">
-  <owner>joe@chormium.org</owner>
+  <owner>joe@chromium.org</owner>
   <owner>{}</owner>
   <summary>I like coffee.</summary>
 </histogram>
@@ -333,13 +333,42 @@ class ExpandOwnersTest(unittest.TestCase):
         r'No emails could be derived from .*empty_OWNERS\.'):
       expand_owners.ExpandHistogramsOWNERS(histograms_without_owners_from_file)
 
+    with self.assertRaisesRegexp(
+        expand_owners.Error,
+        r'The file at .*src/medium/medium/roast/OWNERS does not exist\.'):
+      expand_owners.ExpandHistogramsOWNERS(histograms_with_fake_file_path)
+
+  def testExpandOwnersWithSameOwners(self):
+    """Checks that no error is raised when all owners in a file are already in <owner> elements."""
+    absolute_path = _MakeOwnersFile('same_OWNERS', self.temp_dir)
+    src_relative_path = _GetSrcRelativePath(absolute_path)
+
+    with open(absolute_path, 'w') as owners_file:
+      owners_file.write(
+          'joe@chromium.org')  # Write to the file so that it exists.
+
+    histograms_string = xml.dom.minidom.parseString("""
+<histograms>
+
+<histogram name="Caffeination" units="mg">
+  <owner>joe@chromium.org</owner>
+  <owner>{}</owner>
+  <summary>I like coffee.</summary>
+</histogram>
+
+</histograms>
+""".format(src_relative_path))
+
+    self.assertEqual(
+        expand_owners.ExpandHistogramsOWNERS(histograms_string), [])
+
   def testExpandOwnersWithoutOWNERSPathPrefix(self):
     """Checks that an error is raised when the path is not well-formatted."""
     histograms_without_src_prefix = xml.dom.minidom.parseString("""
 <histograms>
 
 <histogram name="Caffeination" units="mg">
-  <owner>joe@chormium.org</owner>
+  <owner>joe@chromium.org</owner>
   <owner>latte/OWNERS</owner>
   <summary>I like coffee.</summary>
 </histogram>
@@ -358,7 +387,7 @@ class ExpandOwnersTest(unittest.TestCase):
 <histograms>
 
 <histogram name="Caffeination" units="mg">
-  <owner>joe@chormium.org</owner>
+  <owner>joe@chromium.org</owner>
   <owner>src/latte/file</owner>
   <summary>I like coffee.</summary>
 </histogram>