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Re: Issue with order of svn:mergeinfo revision ranges vs. svnmerge-migrate-history.py..

From: C. Michael Pilato <cmpilato_at_collab.net>
Date: Fri, 23 Jan 2009 16:17:58 -0500

Gunter Woytowitz wrote:
> Paul,
>
> Your suspicion is correct, there was a "broken" history, here's a snippet
> from the logs where the copy occurred.
>
> ---------------------------------------------------- r49990 | asdf |
> 2006-10-12 08:38:59 -0400 (Thu, 12 Oct 2006) | 1 line Changed paths: A
> /branches/branch1 (from /branches/branch1:49987)
> ----------------------------------------------------
>
> The branch was accidentally deleted, and then restored a few revs later.
>
> The svnmerge-integrated property before running the script was
> /branches/branch1:1-53669

Yes, svnmerge.py is pretty much history-ignorant. (An interesting feature
for a merge-tracking tool, when you really think about it.) That ignorance
is exactly the kind of thing that the migration script is trying to undo.
This comment in the script describes that:

      # Unfortunately, svnmerge.py tends to initialize using oft-bogus
      # revision ranges like 1-SOMETHING when the merge source didn't
      # even exist in r1. So if the natural history of a branch
      # begins in some revision other than r1, there's still going to
      # be cruft revisions left in NEW_MERGEINFO after subtracting the
      # natural history. So, we also examine the natural history of
      # the merge sources, and use that as a filter for the explicit
      # mergeinfo we've calculated so far.

Unfortunately, there are other comments in the script about how situations
like the one you have are likely to fool the script.

        ### If by some chance it is the case that /path:RANGE1 and
        ### /path:RANGE2 a) represent different lines of history, and
        ### b) were combined into /path:RANGE1+RANGE2 (due to the
        ### ranges being contiguous), we'll foul this up. But the
        ### chances are preeeeeeeetty slim.

We might be able to teach the script to handle this better by taking a
different approach. Rather than checking each individual range in the
proposed mergeinfo against the natural history of the branch individually,
we could fetch the entire natural history of the branch at once (bounded by
the max and min merges, maybe) and take the union of that output with the
proposed mergeinfo. Not sure why I didn't take that approach before ...
possible concerns about performance.

> My general thought is that there should be no way for the migrate script
> to commit an invalid svn:mergeinfo property to the repository. I expect
> there to be bugs in 3rd party scripts, especially with a new complex
> feature, but I also expect the subversion code should be a bit more
> robust and protect itself from this by blocking any commits that contain
> invalid svn:mergeinfo properties. It seems like there is a lot of error
> checking of the svn:mergeinfo property when "reading" the data (ie. the
> errors I'm seeing), but not when the property was "written" to the
> repository. Are there svn:mergeinfo property checks in the subversion
> code on commits? If yes, how did the migrate script bypass them? If no,
> then the checks should be added.

The migration script you ran makes directory property changes to the
repository's filesystem layer. It is *absolutely incorrect* for that layer
to be validating property value formats. The migration script needs,
therefore, to perform that validation itself, perhaps by simply
parsing-and-unparsing the values it proposes to write to the filesystem
(which would cause the mergeinfo to pass through the utility functions that
perform format-checking).

You would not run into this problem if you used, instead, the remote version
of this script, which has to pass its mergeinfo through the Subversion
client layer (and all that sanity-checking logic).

-- 
C. Michael Pilato <cmpilato_at_collab.net>
CollabNet   <>   www.collab.net   <>   Distributed Development On Demand
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Received on 2009-01-23 22:19:17 CET

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