I'm looking for policy or guidance on the following situation. Someone just posted a new question Q1. I noticed that one of the existing answers to another question (Q2) already answers Q1 -- the answer to Q2 happens to be general enough that it answers not just Q2 but also Q1. However, Q1 is not the same question as Q2: they are somewhat related, but they're definitely different questions. In particular, not every good answer to Q2 would answer Q1.
What should I do in this situation? Should I mark Q1 as a duplicate of Q2? Should I avoid marking it as a duplicate? Is it a judgement call? Is there any general policy or guideline?
Where I looked for information on this
The closest related question I could find on MSO was At what point does a question become a duplicate?. There, Shog writes "If a new question is answered by the answers to an old question, I will generally consider it a duplicate. The exception to this is when an answer to the new one does, or potentially could add a significant amount of useful information." So that makes me think it is often OK to mark Q1 as a duplicate of Q2, but not always.
The official guidance says to close a question as a duplicate when it is "sufficiently similar to existing questions and would be answered identically to them", which makes it sound pretty simple: do not mark Q1 as a duplicate of Q2.
If it's relevant, when a question is closed as a duplicate, it is marked with the label "This question already has an answer here:". I suppose this could be taken to suggest that it's OK to mark Q1 as a duplicate of Q2, though personally I doubt that we should be looking to that wording for guidance or policy about duplicates.
I've read Close reason proposal: "Answer exists elsewhere", but that sounds like a different situation to me, so I'm not sure whether the discussion there is applicable. (For those who read Grace Note's answer there: For instance, the
mkdir example is not quite the same situation, because those were two unrelated questions, and the hypothesized answer is not likely to be a good answer to both questions.) I've also read Should we answer questions if the answers can be found elsewhere on the site?, but I'm not 100% clear on how that applies to the situation I gave above.
If you want to see the specific situation where I ran into this most recently, it is this question: Decide whether a DFA accepts the empty language. But I most interested in the general policy/guidance for what to do in this situation, as I see this sort of situation from time to time.