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web commit by http://willu.myopenid.com/: Update information on Monotone support

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joey 2007-08-03 23:24:00 +00:00
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@ -178,6 +178,64 @@ please refer to [Emanuele](http://nerd.ocracy.org/em/)
## [[tla]] ## [[tla]]
## [[bugs/Monotone_rcs_support]] ## [Monotone](http://monotone.ca/)
Available as an unfinished patch curently. There is an unfinished patch in [[bugs/Monotone_rcs_support]].
In normal use, monotone has a local database as well as a workspace/working copy.
In ikiwiki terms, the local database takes the role of the master repository, and
the srcdir is the workspace. As all monotone workspaces point to a default
database, there is no need to tell ikiwiki explicitly about the "master" database. It
will know. (BTW - this is also true of subversion. It might be possible to simplify the svn config?)
The patch currently supports normal committing and getting the history of the page.
To understand the parallel commit approach, you need to understand monotone's
approach to conflicts:
Monotone allows multiple micro-branches in the database. There is a command,
`mtn merge`, that takes the heads of all these branches and merges them back together
(turning the tree of branches into a dag). Conflicts in monotone (at time of writing)
need to be resolved interactively during this merge process.
It is important to note that having multiple heads is not an error condition in a
monotone database. This condition will occur in normal use. In this case
'update' will choose a head if it can, or complain and tell the user to merge.
For the ikiwiki plugin, the monotone ikiwiki plugin borrows some ideas from the svn ikiwiki plugin.
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
saves the page, we check if that is still the current revision. If it is, then we commit.
If it isn't then we check to see if there were any changes by anyone else to the file
we're editing while we've been editing (a diff bewteen the prepedit revision and the current rev).
If there were no changes to the file we're editing then we commit as normal.
All of this should work with the current patch.
It is only if there have been parallel changes to the file we're trying to commit that
things get hairy. In this case the current (implemented but untested) approach is to
commit the web changes as a branch from the prepedit revision. This
will leave the repository with multiple heads. At this stage, all data is saved, but there
is no way to resolve the potential conflict using the web interface.
In the specific case of a branch caused by a web edit, it may be possible to
make monotone use the current web interface. This may be possible because we
know that merging between the two revisions we have (the new branch
and the prepedit revision) involves at most one conflicted file.
We could use `mtn explicit_merge` to merge the revisions. If that
succeeds without conflicts then good. If that fails, then we could
use a special lua merge hook to spit out the conflict marked file
and hand it back to the web interface and then abort the merge. At the same time, we'd have
to modify the 'prepedit' data to include both parents so that when
the user saves again we know we're in this case.
If you get a commit and your prepedit data includes two revids then
we form a commit manually using the automate interface - same way
we currently build the micro-branch. However, while conflicts were being resolved,
someone could have come
along and introduced *another* one. So after forming this merge revision,
you need to go back and check to see if the workspace revision has changed
and possibly go through the whole process again. The repeats until you're
merged.
The end result of all of this is a system that can resolve all web conflicts without race
conditions. (And because of the way monotone works it saves all data, including
both sides of the merge, before the merge. You can go back later and check that
the merge was reasonable.) It still doesn't provide a web-based way of merging multiple
heads that come in through non-web interaction with monotone.