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Re: [merge tracking] Problems with merge info availability and merge interface

From: Karl Fogel <kfogel_at_google.com>
Date: 2006-08-18 22:54:03 CEST

Daniel Rall <dlr@collab.net> writes:
> Note: The most complete solution to many of these problems is to keep
> a full, sync'd copy of all merge info in both WC and repository.
> Considering that this would move Subversion from a centralized
> repository towards a more distributed system, this is not something we
> want to pursue (at least, not at this time). [1]

I don't have good answers for the problems you posed (sorry, just a
time issue at the moment), but I did want to question the article of
faith stated above.

Should a solution be rejected because it tends in the direction of a
distributed system? If solutions to current problems push Subversion
in that direction, it might mean that's a useful direction to go. And
nothing will force us to go farther in that direction than we choose
to, so why worry? :-)

(The reasons given in [1] are understandable... at some point we may
have to ditch the detachable working copies, handy though they are.)

Gratuitous meta-comment courtesy of,

> The complete TODO list of outstanding problems and tasks is tracked
> here:
> http://svn.collab.net/repos/svn/branches/merge-tracking/TODO
> WC -> WC copy/move operations
> -----------------------------
> Such operations are important for refactoring tools (e.g. Eclipse,
> IDEA, etc.). Retaining support for operations offline is quite useful
> in this regard (as you can still run'em on the train, when your
> repository is down, etc.).
> Preserving offline operation is difficult without replicating merge
> info to the client's WC, and keeping that merge info sync'd with the
> repository. Usually, the client must contact the repository to get
> the merge info -- both explicit/inherited, and reflected from all
> revisions of the copy source at its current path -- it needs for the
> parents of the copy source in order to have the complete information
> that needs to be written about the children. The formula's something
> like:
> dest merge info = src merge info + revs of src at path
> We need to use this formula on the client side because subsequent
> merges may change the merge info for the destination path before a
> commit to the repository can set the merge info reflected by the
> copy's source path.
> If the the copy source has no merge info, and the destination path is
> a direct parent of the source path, then we don't need to move any
> merge info (since it will still be gotten from the same parent), but
> we still need to do history tracing to find the oldest revision at
> which the copy source has been at its current path, so that it can be
> included in the merge info for the destination.
> This is not a correctness issue, but rather one of maintaining
> disconnected operation in the face of merge info.
> URL -> URL -> WC merge operations (merge test #19)
> --------------------------------------------------
> A useful operation which takes the difference between URL1@rX and
> URL2@rY, and applies the delta between those trees to a WC.
> The operation currently comes down as one big text delta between the
> files. We can't tell what revs it actually contains, nor how they
> relate to the WC's merge info. Because of this, we can't calculate
> which portions of the delta to apply, and which to filter out (because
> they're already represented by our WC).
> We can preserve the existing behavior without using merge info (as a
> worst case), but this is rather at odds with the goal of introducing
> merge tracking, so we'd like to do something better.
> One option is to send the target paths, plus any WC merge info
> changes, to the repository when procuring the editor, and let the
> editor filter out the merges which are already represented by the WC.
> WC notifications from a merge operation
> ---------------------------------------
> These notifications are received as callbacks indicating that an
> interesting action has occurred on a path.
> For merge tracking purposes, (at least) skips and conflicts must be
> handled, both of which affect merge info set on the WC as the result
> of a merge. Conflicts may also involve entering a conflict resolution
> mode, or necessitate only partial application of the requested merge
> range to conflicted files.
> Notifications of all types generate output. Merging a set of revision
> ranges in a loop may cause multiple notifications for a single WC
> item. This is a rather large difference from existing command-line
> client output (and libsvn_client API behavior).
> This is not a problem so much as question of what we want to do from
> an interface perspective.
> [1] While we could explore the option of sync'ing mergeinfo between WC
> and repository, comparision to other VC systems suggests that this
> would likely require additional restrictions on WCs (e.g. no separable
> WCs unless we have one merge info DB for each directory, which would
> be horrendous), and quite a bit of work. It would be difficult to
> make such a change in behavior compatible with previous versions of
> Subversion.

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Received on Fri Aug 18 22:56:04 2006

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