Comment Sort

The feed has a Sort by select — Hot, New, Top — over the one post.readPosts procedure, and comments are read through the same procedure, but they "keep their fixed sort" (feed and ranking): always the stored hot score. On a thread of any length that hides the newest reply under older well-liked ones, and there is no way to read a conversation in the order it happened. Reddit puts a comment sort directly above every thread, defaulting to its ranked order and offering Top, New and Old beside it.

What it adds

A Sort by select at the head of the Comments section on /post/[id], the same control the feed's toolbar uses, with four options:

• One map. PostSortType gains Old, and PostSortTypeSortByMap gains its entry, so the feed and the comments read one mapping. The feed's select keeps showing Hot, New and Top only; Old is a thread order, not a feed order, and the comment select lists all four.
• The sort applies to the whole tree. The comment store keeps one slice per parent (getSliceOperationData(parentId)); the chosen sort is held once in the store, passed to every branch's readPosts, and changing it clears every slice so each open branch reads page one again under the new order — the feed's own "switch clears and refetches" rule, applied per branch. Replies a reader had expanded stay expanded.
• The cursor already handles every option. getCursorWhere compares compound keys lexicographically in either direction, which is what makes Old's ascending pair page correctly.
• Per visit, not persisted. The sort resets to Hot on the next post, as the feed's does.

What is deliberately not in it

• No "Best". Reddit's Best ranks by the Wilson lower bound of the upvote fraction, which needs up and down counts kept apart; our likeCount is the net sum. Hot already favours a well-liked early reply, and splitting the counter is a schema change for a sort most readers never open.
• No Controversial or Q&A. Controversial needs the same split counts; Q&A needs an author-reply signal the model does not carry.

Key files

Sources

• Evan Miller — how not to sort by average rating — the Wilson lower bound behind Reddit's Best comment sort, and why it needs positive and total counts rather than a net score.