Don't require translation screenshots on description-only changes

* This is a follow-up to crrev.com/c/2328669 with further fine tuning
  from findings in https://crbug.com/1103844#c22.
* The current translation screenshot presubmit check flags modified
  messages:
  1) if the message does not yet have a screenshot, or
  2) if the message content itself changed.
* This CL changes the behavior to for modified messages check in this
  order:
  1) if the message content itself changed -> flag the message.
  2) if the message meaning changed and there is neither an existing
     screenshot nor is a new one added with the CL -> flag the message.
* Important cases to consider: messages that don't yet have a
  screenshot and for which only the message meaning attribute changed
  will require a screenshot, but messages for which only the message
  meaning changed and which already have a screenshot do not require a
  new screenshot. And messages of which only the description attribute
  changed simply never require new screenshots at all.

Bug: 1103844
Change-Id: I0318e685b2182a455dccfb0630ce768f5c990a65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412727
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Commit-Queue: Rainhard Findling <rainhard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808789}

PRESUBMIT.py

@@ -5099,18 +5099,19 @@ def CheckStrings(input_api, output_api):
     removed_ids = old_ids - new_ids
     modified_ids = set([])
     for key in old_ids.intersection(new_ids):
-      if (old_id_to_msg_map[key].FormatXml()
-          != new_id_to_msg_map[key].FormatXml()):
-        sha1_path = input_api.os_path.join(
-          screenshots_dir, key + '.png.sha1')
-        if sha1_path not in new_or_added_paths and \
-           not input_api.os_path.exists(sha1_path):
-          # This message does not yet have a screenshot. Require one.
-          modified_ids.add(key)
-        elif (old_id_to_msg_map[key].ContentsAsXml('', True)
+      if (old_id_to_msg_map[key].ContentsAsXml('', True)
           != new_id_to_msg_map[key].ContentsAsXml('', True)):
           # The message content itself changed. Require an updated screenshot.
           modified_ids.add(key)
+      elif old_id_to_msg_map[key].attrs['meaning'] != \
+          new_id_to_msg_map[key].attrs['meaning']:
+        # The message meaning changed. Ensure there is a screenshot for it.
+        sha1_path = input_api.os_path.join(screenshots_dir, key + '.png.sha1')
+        if sha1_path not in new_or_added_paths and not \
+            input_api.os_path.exists(sha1_path):
+          # There is neither a previous screenshot nor is a new one added now.
+          # Require a screenshot.
+          modified_ids.add(key)
 
     if run_screenshot_check:
       # Check the screenshot directory for .png files. Warn if there is any.

PRESUBMIT_test.py

@@ -2888,6 +2888,22 @@ class StringTest(unittest.TestCase):
         '</message>',
     '</grit-part>')
 
+  NEW_GRDP_CONTENTS5 = (
+    '<?xml version="1.0" encoding="utf-8"?>',
+      '<grit-part>',
+        '<message name="IDS_PART_TEST1" meaning="Meaning with typo.">',
+          'Part string 1',
+        '</message>',
+    '</grit-part>')
+
+  NEW_GRDP_CONTENTS6 = (
+    '<?xml version="1.0" encoding="utf-8"?>',
+      '<grit-part>',
+        '<message name="IDS_PART_TEST1" meaning="Meaning with typo fixed.">',
+          'Part string 1',
+        '</message>',
+    '</grit-part>')
+
   # A grdp file with one ICU syntax message without syntax errors.
   NEW_GRDP_CONTENTS_ICU_SYNTAX_OK1 = (
     '<?xml version="1.0" encoding="utf-8"?>',
@@ -2993,12 +3009,12 @@ class StringTest(unittest.TestCase):
 
   def testModifiedMessageDescription(self):
     # CL modified a message description for a message that does not yet have a
-    # screenshot. Should warn.
+    # screenshot. Should not warn.
     input_api = self.makeInputApi([
       MockAffectedFile('part.grdp', self.NEW_GRDP_CONTENTS3,
                        self.NEW_GRDP_CONTENTS4, action='M')])
     warnings = PRESUBMIT.CheckStrings(input_api, MockOutputApi())
-    self.assertEqual(1, len(warnings))
+    self.assertEqual(0, len(warnings))
 
     # CL modified a message description for a message that already has a
     # screenshot. Should not warn.
@@ -3010,6 +3026,25 @@ class StringTest(unittest.TestCase):
     warnings = PRESUBMIT.CheckStrings(input_api, MockOutputApi())
     self.assertEqual(0, len(warnings))
 
+  def testModifiedMessageMeaning(self):
+    # CL modified a message meaning for a message that does not yet have a
+    # screenshot. Should warn.
+    input_api = self.makeInputApi([
+      MockAffectedFile('part.grdp', self.NEW_GRDP_CONTENTS5,
+                       self.NEW_GRDP_CONTENTS6, action='M')])
+    warnings = PRESUBMIT.CheckStrings(input_api, MockOutputApi())
+    self.assertEqual(1, len(warnings))
+
+    # CL modified a message meaning for a message that already has a
+    # screenshot. Should not warn.
+    input_api = self.makeInputApi([
+      MockAffectedFile('part.grdp', self.NEW_GRDP_CONTENTS5,
+                       self.NEW_GRDP_CONTENTS6, action='M'),
+      MockFile(os.path.join('part_grdp', 'IDS_PART_TEST1.png.sha1'),
+               'binary', action='A')])
+    warnings = PRESUBMIT.CheckStrings(input_api, MockOutputApi())
+    self.assertEqual(0, len(warnings))
+
   def testPngAddedSha1NotAdded(self):
     # CL added one new message in a grd file and added the png file associated
     # with it, but did not add the corresponding sha1 file. This should warn