Consider this situation:
There is this question on another site which I think would be a good candidate for migration to Code Review. What should I consider before flagging the question, or actually migrating it?
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Is the question off-topic on the originating site?
Is the question on-topic for Code Review?
fooas an identifier), stub code (with unimplemented placeholders in places central to the question), or pseudocode (not in a real programming language) are not suitable for Code Review.
Is the question calling for a code review?
If there are answers already, they must be good answers on Code Review too.
Has the question already been asked on Code Review?
If you are unsure whether a question is a good candidate for migration to Code Review, feel free to ask for an opinion in our chat room.
(the bulk of this answer is
plagiarized borrowed from: What is migration and how does it work? - I have taken that and adapted it to focus on Code Review specific concerns)
Migration allows a question that is off-topic on one site in the Stack Exchange network to Code Review (where it will be on-topic) gracefully. It preserves the current revision of the question, all its answers, and any comments on any of those posts, as well as most of the votes.
Just because a question can be migrated, does not mean that it should. If in doubt, vote-to-close the question (it is off-topic), and add a comment suggesting the asker should read the on-topic help for Code Review, and that they may want to re-ask their question there.
This is a perfectly fine alternative to migration, and in many cases it is better.
Down votes are cleared from the question upon its migration.
If a user who has participated in the question does not have an account on the target site, their username is displayed as plain-text until they create an account there.
Answers on the origin site are deleted immediately upon question migration (this causes a reversal of all associated reputation on the origin site).
The question is left as a stub, or pathway to the new site, for 30 days, after which it is automatically deleted (again, this causes a reversal of all associated reputation on the origin site).
A question can rejected by the target community after it has already been migrated if it gets closed as a reason other than duplicate, or gets deleted (usually by the owner) on the target site. When a question which was already migrated gets rejected, the entire process of the migration is reversed. All the answers are returned to the origin site and undeleted (unless the question was deleted on the source site) and are subsequently deleted on the target site.
Code Review has decided to not allow migrations from Stack Overflow (for now?). Therefore, users cannot migrate questions to Code Review just by voting; questions can only be migrated by a moderator of the original site.
The right way to start the migration process of a question to Code Review is to flag the question 'for Moderator Attention' and as part of the custom message, indicate:
This question is off-topic for Stack Overflow because it does not contain a specific question to be answered. However, it is on-topic for Code Review, since the code works, and the asker wants open-ended discussion. Please migrate to Code Review.
Only questions which are younger than 60 days can be migrated to other sites. This rule applies even to moderators on the site.
It goes without saying that there is no point in migrating a question that is on-topic where it is. This sounds silly, but it is possible for questions to be on-topic on multiple sites. Although a question would be great on Code Review, it may also be good-enough on its current site.
The question should be on-topic on Code Review. This should be obvious, but the standard for on-topicness should be even higher for migrated questions. It should be a 'reference quality' question. If there is any doubt about this, don't!
Has the question already been asked here?
If the question already has answers on the source site, then migration is probably not a good solution:
Avoid migrating answered questions. The point of migration is to send the question to an on-topic place when it can get answered. If the OP already has an answer, then we've already defeated the purpose of migration and the destination site won't have anything to do with the question. Avoid migrating these questions unless they are of extremely good quality and risk deletion on the current site.
If there are answers, they would all need to be good answers on Code Review too.