web commit by http://willu.myopenid.com/: Update information on Monotone support
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@ -178,6 +178,64 @@ please refer to [Emanuele](http://nerd.ocracy.org/em/)
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## [[tla]]
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## [[bugs/Monotone_rcs_support]]
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## [Monotone](http://monotone.ca/)
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Available as an unfinished patch curently.
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There is an unfinished patch in [[bugs/Monotone_rcs_support]].
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In normal use, monotone has a local database as well as a workspace/working copy.
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In ikiwiki terms, the local database takes the role of the master repository, and
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the srcdir is the workspace. As all monotone workspaces point to a default
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database, there is no need to tell ikiwiki explicitly about the "master" database. It
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will know. (BTW - this is also true of subversion. It might be possible to simplify the svn config?)
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The patch currently supports normal committing and getting the history of the page.
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To understand the parallel commit approach, you need to understand monotone's
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approach to conflicts:
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Monotone allows multiple micro-branches in the database. There is a command,
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`mtn merge`, that takes the heads of all these branches and merges them back together
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(turning the tree of branches into a dag). Conflicts in monotone (at time of writing)
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need to be resolved interactively during this merge process.
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It is important to note that having multiple heads is not an error condition in a
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monotone database. This condition will occur in normal use. In this case
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'update' will choose a head if it can, or complain and tell the user to merge.
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For the ikiwiki plugin, the monotone ikiwiki plugin borrows some ideas from the svn ikiwiki plugin.
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On prepedit() we record the revision that this change is based on (I'll refer to this as the prepedit revision). When the web user
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saves the page, we check if that is still the current revision. If it is, then we commit.
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If it isn't then we check to see if there were any changes by anyone else to the file
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we're editing while we've been editing (a diff bewteen the prepedit revision and the current rev).
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If there were no changes to the file we're editing then we commit as normal.
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All of this should work with the current patch.
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It is only if there have been parallel changes to the file we're trying to commit that
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things get hairy. In this case the current (implemented but untested) approach is to
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commit the web changes as a branch from the prepedit revision. This
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will leave the repository with multiple heads. At this stage, all data is saved, but there
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is no way to resolve the potential conflict using the web interface.
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In the specific case of a branch caused by a web edit, it may be possible to
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make monotone use the current web interface. This may be possible because we
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know that merging between the two revisions we have (the new branch
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and the prepedit revision) involves at most one conflicted file.
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We could use `mtn explicit_merge` to merge the revisions. If that
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succeeds without conflicts then good. If that fails, then we could
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use a special lua merge hook to spit out the conflict marked file
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and hand it back to the web interface and then abort the merge. At the same time, we'd have
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to modify the 'prepedit' data to include both parents so that when
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the user saves again we know we're in this case.
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If you get a commit and your prepedit data includes two revids then
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we form a commit manually using the automate interface - same way
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we currently build the micro-branch. However, while conflicts were being resolved,
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someone could have come
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along and introduced *another* one. So after forming this merge revision,
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you need to go back and check to see if the workspace revision has changed
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and possibly go through the whole process again. The repeats until you're
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merged.
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The end result of all of this is a system that can resolve all web conflicts without race
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conditions. (And because of the way monotone works it saves all data, including
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both sides of the merge, before the merge. You can go back later and check that
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the merge was reasonable.) It still doesn't provide a web-based way of merging multiple
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heads that come in through non-web interaction with monotone.
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