Comment by dan-robertson
5 years ago
I think a better question is “what if merges were more well behaved,” where “well behaved” means they have nice properties like associativity and having the minimal amount of conflict without auto-resolving any cases that should actually be a conflict.
The problem with using a CRDT is the CR part: there are generally merge conflicts in version control for a reason. If your data type isn’t “state of the repo with no conflicts” or “history of the repo and current state with no conflicts” but something like “history of the repo and current state including conflicts from unresolved merges” then maybe that would work but it feels pretty complicated to explain and not very different from regular git. Also note that you need history to correctly merge (if you do a 3-way merge of a history of a file of “add line foo; delete line foo” with a history of “add line foo; delete line foo; add line foo” and common ancestor “add line foo”, you should end with a history equal to the second one I described. But if you only look at the files you will probably end up deleting foo)
See also: darcs and pijul.
It's perfectly CR to encode a merge conflict as another type of data in the CRDT lattice.
For documents, you might represent this as a merged document, with merge conflict markup inside the merged document - similar to using version control and getting a merge conflict.
Also similar to version control, the merge conflict can be a form of data where a valid CRDT operation is for a user to resolve the conflict. When that resolution is merged with other users, unless there's a conflict in the conflict-resolution, everyone sees the merge conflict go away.
Another valid CRDT operation is when a user modifies their version of the document in the region of the merge conflict prior to seeing the conflict, and broadcasts their edit. Then the merge conflict itself would update to absorb the valid change. In some cases, it might even disappear.
In principle, you can build a whole workflow stack on top of this concept, with sign-offs and reviews, just as with version control. I have no idea how well it would behave in practice.