When I've flagged questions as potential duplicates in the past, a comment was auto-generated to that effect. When I just did the same thing, no such comment was generated (How to structure Util classes in RoR).

The only circumstance I know that was different was that I'd just "answered" the question and had my answer turned into a comment as being "trivial". I then deleted the comment before flagging the question, on the assumption that a flag-related comment would be auto-generated.

Anyone know what's up? Was the system behavior recently changed?


The system checks all the previous comments to see if a link to that question already exists somewhere in the comments. If it does, it won't create another link to that question since it already exists.

However, based on experience, this check is fairly loose and inaccurate. It will catch links in both the forms of /q/# and /questions/#/slug. From what I can tell, it simply scan the links for the ID number extracted out of the URL you're closing as a duplicate, and applies it to a basic pattern such as stackoverflow.com/*/#/*, so it basically catches any question URL which would use that ID number.

Note that this does not catch short URLs for answers (in the form of /a/#) even though the answer may be on that question, since the question's ID number does not actually appear anywhere in that URL.

I'm not 100% on whether deleted comments are supposed to be included in that check, but my guess would be that they are. Since your answer-converted-to-comment contained a matching link to the question, a new link would not be generated.


Based on my recent experience, when I cast a close vote as duplicate, an auto remark was generated with a link to the duplicate.

The only time it wasn't generated was when I created a manual comment before casting the close vote. I assume it's only generated if you don't create a manual comment.

I guess your answer that was converted to a comment and then was deleted still counts as a manual comnent that prevents the generation of the auto comment.

  • Makes sense. Think it's worth submitting as a defect (i.e. the behavior in the case of a deleted comment)? – Peter Alfvin Jul 12 '13 at 4:10

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