This question arises from a debate between friends about what is "technically" more correct in this sentence:
"You don't happen to have read <book name>, do you?"
Should the question be "do you" as in
"You don't happen…, do you?"
or "have you" as in "have you read"?
(I understand that there are better ways to write this sentence.)
Best Answer
Bear in mind: The issue here is about the one-off feature of "read that book" and the present simple in English.
I happen to like chocolate, don't I? I don't happen to like pastry, do I?. General statements about a thing or situation are in the present simple.
happen to does not work well with "a single occurrence of a situation" such as: You don't happen to have read that book. For the present simple to work, you need a general statement: You don't happen to read mystery stories very often, do you?
You don't happen to ride your bike there every day, do you? You didn't happen to read that book, did you?
Your sentence is not grammatical in English for the present simple, it is not a general statement. You don't happen to like mystery stories, do you? [general statement]
So, the issue is not the tag. The issue is the predicate: read that book. single occurrence. Typically in English we say:
I don't happen to like answering grammar questions much, do I? [general question re grammar questions.]
BBC English_ Present Simple
For a single occurrence like here (read that book), you can use just about any tense other than the present simple.
[Personal note: Had I not taught English for many years and subsequently become a translator, I never would have been able to figure this out. :)]
PS: In utterances such as: I happen to like a short walk before breakfast. That is OK, as it is a general statement.