Thoughts on file ids

[Martin Geisler]

Martin Pool <mbp at canonical.com> writes:

> On 18 May 2011 10:33, Francis Devereux <francis at devrx.org> wrote:
>> On 17 May 2011, at 01:53, Robert Collins wrote:
>>>
>>> In particular I think you will want tests for the various
>>> pathologies on merge that both git and hg suffer from (and we don't)
>>> - it would be a darn shame to generalise bzr to work more
>>> efficiently with those systems by downgrading its behaviour to match
>>> them.
>>
>> As a user I would be very interested to hear what those merge
>> pathologies are, if someone has time to explain them. At work we are
>> selecting the VCS for a new project and are probably going to choose
>> hg or git but we still have time to change our minds and I'd much
>> rather find out why bzr is better than the others before instead of
>> after we've made our decision! (so far my attitude has been "as long
>> as it's a DVCS it'll be way better than what we have now (svn)")
>
> The kind of thing Robert is referring to here is cases like renaming a
> subdirectory, and then later merging in a branch that originated
> before that and changes or adds some files in that directory. Or
> similarly, running log on one of the files in the directory or the
> directory itself, or renaming a file and also changing it. Because bzr
> handles directories as first-class objects, and gives them a long-term
> id, it has in the past shown to handle these much better than the
> alternatives.

I note you write 'in the past' -- I just tested renaming a directory and
merging in a change made in the old directory and it worked the same in
all major versions from 1.0 to 1.8.3 (I could not get Mercurial 0.9
running on my machine). The scenario is:

  $ hg init repo
  $ cd repo
  $ mkdir foo
  $ echo hello > foo/hello.txt
  $ hg add
  adding foo/hello.txt
  $ hg commit -m hello

Rename directory:

  $ hg rename foo bar
  moving foo/hello.txt to bar/hello.txt
  $ hg commit -m rename

Go back and change hello:

  $ hg update 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo goodbye >> foo/hello.txt
  $ hg commit -m goodbye
  created new head

Now merge

  $ hg merge
  merging foo/hello.txt and bar/hello.txt to bar/hello.txt
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat bar/hello.txt
  hello
  goodbye


-- 
Martin Geisler

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