What to do with questions that are unanswered but answered in the comments? [duplicate]

Question

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How to handle questions which are answered in the comments?

I was going through the unanswered questions today and came across JasperReports | Bad exception in PDF exporting. Reading the comments the user figured out the answer and posted it in the comments. Usually I leave them a comment telling them they should add an answer and mark it as accepted. But in this case it is a low rep user, that has not logged back in for several months.

It feels wrong to answer it myself, considering the answer definitly would not have been my first guess. At the same time it will continue to be listed as unanswered.

So what should we do with questions like these?

Answer 1

Vote to close these questions (self-answered in comments, no detail) as too localized, or flag for moderator attention if you don't have vote to close privileges.

The "answer" is only of interest to him (I solved it using blah-blah library), unless he comes back and explains in detail what he did, which seems unlikely.

Answer 2

In cases where the answer could be of value to someone else in the future, I'll post the answer myself.

I typically fix up spelling, grammar and formatting, but nothing else. I also add a note like "originally written by [author name] in a comment." Before submitting, I tick the CW box. Finally, I leave a comment notifying the original author of what's I did and say that I'll remove my answer if he posts one of his own.

In cases where the original author does come back and post, I almost always give a "learning to use the site" upvote even if the answer is only mediocre.