N Participants Resolve an N-way Conflict

[meejah]

As a participant, when N other participants and I all edit a file at the same time, I want to be able to see that there are N conflicting versions of the file and be able to resolve the conflict by supplying a version of the file (perhaps one of the N conflicting versions, perhaps another version I construct) which becomes the “head” as seen by all participants. This will allow everyone to continue to collaborate by giving everyone a consistent view of the file after a conflict occurs.

Note: It is up to the user to figure out which version they want or construct a desirable version. They will likely need external tools not integrated into this version control system (in other words, this story implies no external editor integration).

• Detect a conflict (see 'detection of conflicts': https://github.com/LeastAuthority/magic-folder/blob/master/docs/proposed/magic-folder/multi-party-conflict-detection.rst#detection-of-conflicts)
• Snapshots have multiple "parent" pointers
• When a conflict is detected, "conflict" files are created (e.g. foo.conflicted, foo.conflicted.Alice, etc -- see https://github.com/LeastAuthority/magic-folder/blob/master/docs/proposed/magic-folder/multi-party-conflict-detection.rst#a-possible-ui-for-resolving-conflicts)
• When "conflict" files are removed / renamed, a new Snapshot is created and uploaded (this Snapshot will have at least 2 "parent" pointers, possibly more if it's a conflict with more than one other user). This "resolves" the conflict.