Dear fellow org-ers,

it's time to pay back to the community.

I'm coming back to a feature request by Torsten Wagner, who needed an
org link to a specific version of a file for his lab book (see
http://permalink.gmane.org/gmane.emacs.orgmode/15774). Recently I needed
the same thing to organize a collaboration project. I am therefore happy
to announce org-git-link.el, which implements this feature. The emacs
lisp file (which is all you need) is attached for convenience. The
README file can be found together with a testsuite at
http://github.com/ReimarFinken/org-git-link.

`org-git-link.el' defines two new link types. The `git' link type is
meant to be used in the typical scenario and mimics the `file' link
syntax as closely as possible. The `gitbare' link type exists mostly for
debugging reasons, but also allows e.g. linking to files in a bare git
repository for the experts. Typical uses look like

  - [[git:../data/result.png::master@{3.10.2009}]]
  - [[git:~/repo/data/results.png::nobelprize]] (Tag nobelprize)
  - [[gitbare:../.git::nobelprize:data/results.png]] (Specify git dir
    and object reference directly)

Following any of the git links checks out the specified version into
a temporary file. Care is taken that each file is checked out once,
even when they are referenced by different search strings (e.g. once
by branch name and once by tag). The file is supsequently opened
using `org-open-file', which does the right thing for non-text files
as well.

As an org mode is a simple text file, a git link can of course be
inserted directly as a string. For your convenience two functions
creating links automatically have been defined:

org-git-store-link: This function is automatically added
     to `org-store-link-functions'. When `org-store-link'
     (usually bound to `C-c l') is called in a buffer whose
     file is in a git repository, it creates a git link to the
     file version corresponding to the current branchname and
     date. The link is then added to `org-stored-links', from
     where it can be inserted with `org-insert-link(-global)',
     usually bound to `C-c C-l'.

org-git-insert-link-interactively: This function
     interactively asks for a file name, a search string, and
     a description. The corresponding link is then inserted at
     point. Currently the only advantage over writing the link
     directly is file completion. Completion of the search
     string with the help of current tags and branch names
     might be implemented at a later stage, if demand exists.

Activate by putting the file somewhere in your load-path and evaluate
(require 'org-git-link). Enjoy!