Don't automatically delete comments with useful content on migration

Question

When a question is migrated, any comment that mentions the name of the target site is automatically deleted. This makes sense when the comment is “you should have posted on <site>”, but comments that also contain other useful information, such as suggestions of possible improvements in the question¹ or of possible places where to look for an answer also get deleted.

While comments are meant to be temporary, they are normally not deleted without human review. A comment on a recent question is likely not past its read-by date and should not be deleted without a good reason.

Comments like “post on <site>” when the question is now on <site> can be confusing, but deleting comments can also be confusing, even to seasoned users (examples: 1 2). It's easy enough to flag a comment that should be deleted², and very difficult to find a comment that got deleted by the migration (it's still visible but not under a public URL: you have to know where to look³ and to know that you should be looking there).

Please do not automatically delete comments upon migration unless they only say “you should have posted on <site>” and nothing else. The heuristic should default to keeping the comment. If there's no good heuristic, that's fine: just remove that feature altogether.

¹ _{Yes, a question can be both of good enough quality to migrate and yet not so perfect that it can't be improved.}
² _{When I cast the last close vote on a question that gets migrated, I routinely visit it on the target site to at least retag it, and possibly flag now-obsolete comments such as “this belongs on <nickname for the target site>”.}
³ _{Add ?noredirect=1 to the original URL, i.e. http://ORIGINALSITE.stackexchange.com/questions/NUMBER?noredirect=1}

Answer 1

I agree; sometimes comments mention another site but also provide other guidance, like "X is on topic there but they have special requirements; see (help link)".

Let's treat comments that link to the current site the same way we treat comments containing certain magic words: a single flag deletes them. Yes, this means that "you should post this on X" gets through initially, but it's easy to clean up, even by the person who migrated it. (Trust me; moderators sometimes forget to clean up comments, and, of course, if it's a community migration the close-voters can't clean them up first.)

Answer 2

Six years later, and this just happened again.  I just posted a third comment on this question on U&L and then cast the final vote to close it and migrate it to Stack Overflow.  For fun, I then clicked to see the migrated question, and was surprised to see that only two of the comments survived the migration: the first and the third (mine).

The first two comments were upvoted.  The third one, naturally, was not, inasmuch as I had posted it only seconds before.  The one that was deleted,

You might be able to get help over on stackoverflow.com but you'll need to give a lot more information.  Unfortunately this is not a Unix & Linux question. – Philip Couling Apr 13 at 14:15

was probably more important (“you'll need to give a lot more information”) than the first one (“I’m voting to close this question because it is about Windows related task”).

I realize now that Philip’s comment was deleted (not migrated) because it mentioned “stackoverflow.com” (it wasn’t even a link!).  I’ll offer a suggestion: delete comments only if they’re < 42 characters.

P.S. / Disclaimer: I didn’t vote to migrate the question.  I know that it is unclear, and should have been improved before being migrated, and so I voted “Needs details or clarity”.  But three other people had already voted “This question belongs on stackoverflow.com”.