Subject: Re: How to deal with historic tar-balls

From: Neal Kreitzinger <[email-masked]>
Date: Thu, 05 Jan 2012 09:25:22 -0600

On 12/31/2011 1:04 PM, nn6eumtr wrote:
> I have a number of older projects that I want to bring into a git
> repository. They predate a lot of the popular scm systems, so they
> are primarily a collection of tarballs today.
>
> I'm fairly new to git so I have a couple questions related to this:
>
> - What is the best approach for bringing them in? Do I just create a
>  repository, then unpack the files, commit them, clean out the
> directory unpack the next tarball, and repeat until everything is
> loaded?
>
> - Do I need to pay special attention to files that are
> renamed/removed from version to version?
>
> - If the timestamps change on a file but the actual content does not,
>  will git treat it as a non-change once it realizes the content
> hasn't changed?
>
> - Last, if after loading the repository I find another version of the
>  files that predates those I've loaded, or are intermediate between
> two commits I've already loaded, is there a way to go say that commit
> B is actually the ancestor of commit C? (i.e. a->c becomes a->b->c if
> you were to visualize the commit timeline or do diffs) Or do I just
> reload the tarballs in order to achieve this?
>
The git-rm manpage contains instructions under the "vendor code drop"
section on how to do this.  I imagine you will want to do each one
manually instead of queueing them up in a script because you are likely 
going to want to do appropriate clean up of the working tree in each 
iteration before committing.  This is where you would review 
renames/removes with git-status before you git-add and git-commit. 
Also, if you are tracking permissions in git (the executable bit) then 
you will want to filter out any noise generated by frivolous permissions 
changes between the tarball contents.

In regard to inserting tarballs into the history that depends on when 
you think you plan on doing that.  You are only going to be able to do 
that before the history is published (made "public" for other repos to 
pull down).  Otherwise you will be rewriting published history which is 
a big no-no (see git-rebase manpage).  I suggest you do your homework 
and order them properly before you start because that will be less work. 
  If you still find that you missed something then you can use 
interactive git-rebase to insert.  I'm assuming a single "master" branch 
with linear history is your desired end result.  If you want to create 
maintenance branches showing release history then you will definitely 
need to do your homework first (see gitworkflow manpage).

If you venture into rebase territory by rewriting history (inserting 
missed tarballs in between older commits) you will need to be sure to 
review your automatic merge resolutions.  Git only generates 
merge-conflicts on same-file-same-line conflicts.  It will auto-merge 
same-file-different-line changes.

You also need to ask yourself if you really need a history of all those 
versions.  To exaggerate, if all you really need is the current state 
then you need to ask yourself if it's worth the effort to record the 
previous states.  Maybe what you want is something in-between (a happy 
medium).

In regard to the 'start-over' method of inserting missed tarballs you 
would just git-reset --hard to the commit you want to insert on-top-of, 
add the tarball, and then re-apply the subsequent tarballs.  If you are 
doing cleanup between commits then the rebase or cherry-pick of the 
already cleaned-up subsequent commits from the "old-branch" (previous 
attempt) onto the 'do-over' branch will likely be easier.  (You can just 
do 'git branch old-branch' on your branch before the git-reset --hard 
(do-over) and that will give you a "backup copy" of the "previous 
attempt" called "old-branch" that you can salvage already-done-work from 
by using rebase or cherry-pick.)

Hope this helps.

v/r,
neal