[ANN] tagmerge - an extension for merging .hgtags

[Greg Ward]

On Thu, Feb 4, 2010 at 12:30 AM, Qi Yang <qi.yang137 at gmail.com> wrote:
> The following is the link to an extension I wrote for merging .hgtags file.

Actually, it's not an extension.  It's a script.

> https://q6yang@bitbucket.org/q6yang/tagmerge/

There are a bunch of code style issues: long lines, trailing
whitespace, etc.  Please run Matt's check-code.py script on your
script.  check-code.py uses the filename to know what checks to apply,
so you need to fool it, e.g.

  ln -s tagmerge tagmerge.py
  ~/src/hg-crew/contrib/check-code.py tagmerge.py

Now to the real stuff:

> def readtags(filename):
>    '''parsing .hgtags file'''
>     tags = {}
>     with open(filename) as f:
>          for line in f.readlines():
>              tagid, tagname = line.split(" ")
>              tags[tagname.strip()] = tagid
>     return tags

That won't work.  You cannot simply store .hgtags in a dictionary.
Tag names can be repeated and order matters.  Play around with
deleting and moving tags to see how that works:

  hg tag -r 5 foo
  hg tag -f -r 7 foo
  hg tag --remove foo
  hg tag -r 4 foo

The resulting .hgtags looks very strange... until you think about what
happens when you merge two .hgtags that have had similar games played.

If it's any consolation, I made the exact same mistake around a year
ago, when I posted my naive attempt at a tag-merging script.  Since
then, Matt cunningly tricked me into becoming an .hgtags expert, so
now I get to handle these sorts of things.  ;-)

See mercurial/tags.py for code that understands how to read tags.  You
probably want to reuse _readtags().

IMHO this is something that should be improved in core Mercurial.  I
think your ultimate goal should be a patch to mercurial/tags.py with
all the tricky tag-merging logic, and then a front-end script in
contrib/.  For now, keeping things in a little standalone script is
probably the right thing to do.  Once that works it should be clear
what belongs in tags.py.

Another comment:

> def pickmergetool(ui):
>     '''pick merge tool for merging conflict: pick the highest priority one
> or use simple merge if there are no other merge tools'''
>     tools = {}
>     for k,v in ui.configitems("merge-tools"):
>         toolname = k.split('.')[0]
>         if toolname not in tools:
>             tools[toolname] = int(_toolstr(ui, toolname, "priority", "0"))
>     if len(tools) == 0 or toolname == 'tagmerge':
>         ui.debug("simplemerge will be used\n")
>         return None
>     tools = sorted([(-p,t) for t,p in tools.items()])
>     priority, pickedtool = tools[0]
>     ui.debug("Pick merge-tool %s" % (pickedtool))

Isn't this logic already implemented somewhere in core Mercurial?  If
it's not available to you in a reusable form, please submit a
refactoring patch to correct that.

> def writenewtags(filename, newtags):
>     '''write non-local tags to the local .hgtags file'''
>     with open(filename, 'r+') as f:
>         for line in f.readlines():
>             tagid, tagname = line.split(" ")
>             for itemtagname, itemtagid in newtags.items():
>                 if tagid == itemtagid and tagname != itemtagname:
>                     f.write(itemtagid + ' ' + itemtagname)
>                     break
>         f.write('\n')

And this is buried deep in localrepo.py.  It should probably be
factored out to tags.py for reusability.  Please submit another
refactoring patch for that!

Thanks!

Greg