right way to reverse engineer a "virgin" branch?

[Eric Siegerman]

On Thu, 2011-04-21 at 22:15 -0700, Chris Hecker wrote:
> I have two websites, one on mediawiki, and one on wordpress, and I've 
> got them in bzr.  The problem is, because I'm dumb, I didn't start
out 
> the branch with a virgin distribution branch from 
> wordpress.org/mediawiki.org, and then branch that to my site(s) [...]
>
> So, now I'd like to "unmerge" them, so to speak, so that updates from 
> the original code are easier.  What's the best way to do this?
> 
> I have [one of the sites] at mediawiki-1.15.5, and I 
> want to update it to 1.16.4.

As long as your branch contains a pristine copy of
mediawiki-1.15.5 somewhere in its mainline history, setting this
up will be a lot easier than you think.  (And a lot easier than
my description suggests...)

Definitions:
  - $my_wiki: The branch containing both a pristine 1.15.5 and
    your subsequent local changes
  - $pristine_rev: the revision containing that pristine 1.15.5
  - $upstream: the name of the new branch you want to create;
    this is the one that will contain only pristine MediaWiki
    distributions.

Here's what to do:

First, back up $my_wiki!

Then:
    $ bzr branch -r$pristine_rev $my_wiki $upstream
That creates $upstream as a branch of $my_wiki, but ensuring that
the latest revision in $upstream is a pristine copy of
mediawiki-1.15.5.

    $ cd $my_wiki
    $ bzr missing --line

That should report that $my_wiki contains extra revisions, i.e.
the ones containing all your local changes since 1.15.5.  It
should *not* report $upstream as containing any extra revisions.

Now make $upstream forget that it was branched from $my_wiki:
    $ vim $upstream/.bzr/branch/branch.conf
    # delete the "parent_location=" line

The next step is to tell $my_wiki that it's a child of $upstream:
    $ vim $my_wiki/.bzr/branch/branch.conf
    # add a "parent_location=" line; the value should be
    # the location of $upstream.  (It can be either a URL
    # or a relative pathname.)

If all has gone well, you're now in the state you wanted:
  - the newest revision in $upstream is a pristine
    mediawiki-1.15.5

  - $my_wiki contains that (not just that content, but that exact
    Bazaar revision) plus your subsequent local changes

  - $my_wiki thinks it was branched from $upstream (though in
    fact it was the other way around)

That means that at this point, after updating $upstream to
MediaWiki 1.16.4, you can bring the changes into $my_wiki using a
normal merge:

    $ cd $my_wiki
    $ bzr merge


> What do I do about stuff that I don't want in the virgin branch, but
do 
> in site?

You won't have that specific situation, because $upstream doesn't
contain *any* local files, but you might well have a similar
problem: files in MediaWiki 1.15.5 that are no longer present in
1.16.4.  The easiest solution is to clear out the old release
before importing the new one:
    $ cd $upstream

    # Get rid of everything except .bzr
    $ rm -r *   # [sic]
    $ ls -a
    # rm any hidden "." files (other than .bzr of course)

Now:
  - untar the new distribution into $upstream
  - "bzr mv --after" any files that were renamed upstream
  - "bzr add" any remaining untracked files

By deleting *all* of the working files before you unpacked the
tarball, by definition you deleted any files that aren't in the
new release :-), and so they won't be there to clutter things up.

At this point, you can commit the new release, then merge it into
$my_wiki.

  - Eric