Re: More Beginning Git Questions

From: tactical <a5158017@nepwk.com>
Date: Sep 26, 2011, 00:56 UTC
Message-ID: <1aec7c1qq0n56.sxybjnsj6ngr$.dlg@40tude.net>
In-Reply-To: <20110926003447.GG10955@localhost.localdomain>

Konstantin Khomoutov wrote:

Show 12 quoted lines

>>>> From what I read, detached heads are subject to garbage collection.
>>>  
>>> No, HEAD is protected against garbage collecting.  To be sure you
>>> should name a branch when switching branches, though reflog would
>>> protect you for 30 days (by default) even if you don't do that.
>> 
>> So Git doesn't really support anonymous branching as part of a normal
>> workflow.
> 
> I perceive a certain logical fallacy here: you cannot switch between
> anything anonymous because to switch, you should somehow identify
> something to switch to--a name in whatever sense we put into this word.

In Mercurial, you can just update to a particular changeset (and you identify that changeset by repository-local revision number or globally unique ID) and then commit again. The point is that there's no need to give a label to a head in Mercurial (although you can if you want to, using Mercurial bookmarks, which are basically the same as what Git uses).

Here's an example of anonymous branching:

    c:\test>hg init

    c:\test>echo test>foo

    c:\test>hg commit --addremove -m initial
    adding foo

    c:\test>echo first>>foo

    c:\test>hg commit -m first

    c:\test>hg log
    changeset:   1:3e895ec28d6c
    tag:         tip
    user:        tactical
    date:        Mon Sep 26 01:39:46 2011 +0100
    summary:     first

    changeset:   0:b51644bb3450
    user:        tactical
    date:        Mon Sep 26 01:39:40 2011 +0100
    summary:     initial

    c:\test>hg update 0
    1 files updated, 0 files merged, 0 files removed, 0 files unresolved

    c:\test>echo second>>foo

    c:\test>hg commit -m second
    created new head

    c:\test>hg glog
    @  changeset:   2:35c82a7e7de1
    |  tag:         tip
    |  parent:      0:b51644bb3450
    |  user:        tactical
    |  date:        Mon Sep 26 01:40:10 2011 +0100
    |  summary:     second
    |
    | o  changeset:   1:3e895ec28d6c
    |/   user:        tactical
    |    date:        Mon Sep 26 01:39:46 2011 +0100
    |    summary:     first
    |
    o  changeset:   0:b51644bb3450
       user:        tactical
       date:        Mon Sep 26 01:39:40 2011 +0100
       summary:     initial

I now have two anonymous branches, and these will never be garbage collected. I can easily update to either branch with "hg update 1" or "hg update 2" (or "hg update 0" again, if i want to create yet another anonymous branch).

> As I understand, by switching between branches in Mercurial you mean
> switching between directories with clones;

No.  Clones are a different topic.

Show 5 quoted lines

> As to branches, they do have names in Git but they are very loosely
> coupled with their names: tag a tip of some branch (to still have a
> handle on that tip commit) then delete that branch--there will be no
> traces of that branch's name left, the branch's name is not encoded in
> its history in any way.

Git branch names are basically the same as Mercurial bookmarks. The difference is that in Mercurial you don't *have* to use bookmarks.

Show 5 quoted lines

> The branch names is just a way to not mess with
> SHA-1 names of commits (and to have references to those commits to keep
> them out of consideration for garbage collection).
> Hence the idea to demand support for anonymous branches in Git's model
> is just unfounded.

I think it's simply a weakness of Git. There are zero problems with anonymous branching in Mercurial, and it's a very powerful and simple system.