[extractor/youtube] Fix continuation loop with no comments (#7148)

Deep check the response for incomplete data.

Authored by: coletdjnz

yt_dlp/extractor/youtube.py

@@ -3314,7 +3314,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 expected_comment_count = self._get_count(
                     comments_header_renderer, 'countText', 'commentsCount')
 
-                if expected_comment_count:
+                if expected_comment_count is not None:
                     tracker['est_total'] = expected_comment_count
                     self.to_screen(f'Downloading ~{expected_comment_count} comments')
                 comment_sort_index = int(get_single_config_arg('comment_sort') != 'top')  # 1 = new, 0 = top
@@ -3385,7 +3385,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         if not tracker:
             tracker = dict(
                 running_total=0,
-                est_total=0,
+                est_total=None,
                 current_page_thread=0,
                 total_parent_comments=0,
                 total_reply_comments=0,
@@ -3418,11 +3418,13 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             continuation = self._build_api_continuation_query(self._generate_comment_continuation(video_id))
             is_forced_continuation = True
 
+        continuation_items_path = (
+            'onResponseReceivedEndpoints', ..., ('reloadContinuationItemsCommand', 'appendContinuationItemsAction'), 'continuationItems')
         for page_num in itertools.count(0):
             if not continuation:
                 break
             headers = self.generate_api_headers(ytcfg=ytcfg, visitor_data=self._extract_visitor_data(response))
-            comment_prog_str = f"({tracker['running_total']}/{tracker['est_total']})"
+            comment_prog_str = f"({tracker['running_total']}/~{tracker['est_total']})"
             if page_num == 0:
                 if is_first_continuation:
                     note_prefix = 'Downloading comment section API JSON'
@@ -3433,11 +3435,18 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 note_prefix = '%sDownloading comment%s API JSON page %d %s' % (
                     '       ' if parent else '', ' replies' if parent else '',
                     page_num, comment_prog_str)
+
+            # Do a deep check for incomplete data as sometimes YouTube may return no comments for a continuation
+            # Ignore check if YouTube says the comment count is 0.
+            check_get_keys = None
+            if not is_forced_continuation and not (tracker['est_total'] == 0 and tracker['running_total'] == 0):
+                check_get_keys = [[*continuation_items_path, ..., (
+                    'commentsHeaderRenderer' if is_first_continuation else ('commentThreadRenderer', 'commentRenderer'))]]
             try:
                 response = self._extract_response(
                     item_id=None, query=continuation,
                     ep='next', ytcfg=ytcfg, headers=headers, note=note_prefix,
-                    check_get_keys='onResponseReceivedEndpoints' if not is_forced_continuation else None)
+                    check_get_keys=check_get_keys)
             except ExtractorError as e:
                 # Ignore incomplete data error for replies if retries didn't work.
                 # This is to allow any other parent comments and comment threads to be downloaded.
@@ -3449,15 +3458,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 else:
                     raise
             is_forced_continuation = False
-            continuation_contents = traverse_obj(
-                response, 'onResponseReceivedEndpoints', expected_type=list, default=[])
-
             continuation = None
-            for continuation_section in continuation_contents:
-                continuation_items = traverse_obj(
-                    continuation_section,
-                    (('reloadContinuationItemsCommand', 'appendContinuationItemsAction'), 'continuationItems'),
-                    get_all=False, expected_type=list) or []
+            for continuation_items in traverse_obj(response, continuation_items_path, expected_type=list, default=[]):
                 if is_first_continuation:
                     continuation = extract_header(continuation_items)
                     is_first_continuation = False