Compress fully-removed comment chains

When a chain of comments has been fully removed, this will display a
single marker like "Removed by admin: 8 comments by 2 users" instead of
individual "Comment removed by site admin" markers for each one.

tildes/tildes/models/comment/comment_tree.py

@@ -3,6 +3,7 @@
 
 """Contains the CommentTree and CommentInTree classes."""
 
+from collections import Counter
 from datetime import datetime
 from typing import Iterator, List, Optional, Sequence, Tuple
 
@@ -51,6 +52,8 @@ class CommentTree:
 
         self.tree = self._prune_empty_branches(self.tree)
 
+        self._add_removed_markers()
+
         self._count_children()
 
     def _count_children(self) -> None:
@@ -131,6 +134,37 @@ class CommentTree:
 
         return pruned_tree
 
+    def _add_removed_markers(self) -> None:
+        """Add markers to chains of removed comments with more info.
+
+        When displaying a comment tree, these markers should be displayed to users
+        that can't view the removed comment, and stop recursing down the branch.
+        """
+        # work backwards so all replies are always processed first
+        for comment in reversed(self.comments):
+            if not comment.is_removed:
+                continue
+
+            # we can only compress when all descendants are also removed - checking
+            # for this attr works because it's only added after passing this check
+            if not all(
+                hasattr(reply, "removed_comments_by_user") for reply in comment.replies
+            ):
+                continue
+
+            comment.removed_comments_by_user = Counter({comment.user: 1})
+
+            # add all the descendants' counts onto this comment's
+            for reply in comment.replies:
+                comment.removed_comments_by_user += reply.removed_comments_by_user
+
+            num_comments = sum(comment.removed_comments_by_user.values())
+            num_users = len(comment.removed_comments_by_user)
+            if num_comments > 1:
+                comment.removed_marker = (
+                    f"Removed by admin: {num_comments} comments by {num_users} users"
+                )
+
     def __iter__(self) -> Iterator[Comment]:
         """Iterate over the (top-level) Comments in the tree."""
         for comment in self.tree:

tildes/tildes/templates/macros/comments.jinja2

@@ -30,9 +30,10 @@
     >
       {{ render_comment_contents(comment, is_individual_comment) }}
 
-      {% if comment.replies is defined and comment.replies %}
+      {# Recursively display reply comments, unless we hit a "removed marker" #}
+      {% if comment.replies and
+           (request.has_permission("view", comment) or not comment.removed_marker) %}
         <ol class="comment-tree comment-tree-replies">
-          {# Recursively display reply comments #}
           {{ loop(comment.replies) }}
         </ol>
       {% endif %}
@@ -74,7 +75,11 @@
         {% if comment.is_deleted %}
           <div class="is-comment-deleted">Comment deleted by author</div>
         {% elif comment.is_removed %}
-          <div class="is-comment-removed">Comment removed by site admin</div>
+          {% if comment.removed_marker %}
+            <div class="is-comment-removed">{{ comment.removed_marker }}</div>
+          {% else %}
+            <div class="is-comment-removed">Comment removed by site admin</div>
+          {% endif %}
         {% endif %}
       {% endif %}