nogit: Using git to track files without the user using git

Summary
=======
Let's see, nogit is a very simple tool that uses git under the hood to
allow for collaboration on files, but without requiring the
collaborators to invoke git commands. Any time a user might invoke
"git commit", or "git push", or "git pull", etc. the user instead just
invokes "nogit sync". And the user will not be prompted to fill out a
commit message or to resolve conflicts, etc.

This is not intended as an alternative to git. If you're already using
git, please continue to do so, (creating clean code history with
detailed commit messages, etc.). Instead, nogit is intended for text
files that you otherwise wouldn't have even put into git. And
specifically, it's only suitable for text files where a naive "union
merge" is the right thing. To be precise, a nogit merge will always
silently give you "both sides" of any merge conflict, and will not
provide any conflict markers, (it won't even indicate that any
conflict happened). It also won't give any predictable behavior on the
ordering of lines in cases like this. So if your data isn't safe
against that kind of corruption, then you'll probably not want to use
it with nogit.

The original data for which nogit was invented for was a simple TODO
list where different people were adding items they wanted to work on,
then removing them when they completed them. These people wanted to
keep each other informed about their activities, so they wanted to
share items in a single file. But there was no functional significance
to the order of items. Finally, it was unlikely that two people would
edit any one item in two different ways, (and even if they did it
would be trivial and painless to sort this out after the fact).

Installation
============
The nogit implementation is a simple bash script named "nogit". To
install it, simply copy it to a directory on your PATH. Or, if you'd
like to be able to follow along with nogit changes from a git
repository, you might create a symlink from a directory on your PATH
to the nogit script in the git repostiory.

Usage
=====
Presumably, you've been pointed to a repository which is intended to
be used with nogit. These repositories are often paired with a
"parent" repository that is being tracked with git. If so, the
procedure for cloning should look something like this:

	git clone /url/of/parent
        cd parent
        nogit clone /url/of/nogit/child

And after that, you can run "nogit sync" whenever convenient, (when
you've made changes or you think there might be upstream changes to
the files being tracked in the nogit repository). Note that "nogit
sync" should not ever ask for user input, so it's appropriate to call
"nogit sync" from an autoamted system, (such as a text editor's hook
when saving a file).

Integration with emacs
======================
If you're an emacs user, here is some code you could put into your
.emacs file to have "nogit sync" called automatically for you for any
nogit-controlled files whenever you open one, begin editing it, or
save it:

  ; Run "nogit sync" if there is a .noggit directory here.
  ;
  ; Note: There is an important protection built into this implementation:
  ;
  ;       We bind 'in-nogit-sync and test whether it's bound to avoid
  ;       infinite recursion. This could otherwise come about because
  ;       the revert-buffer function could trigger the find-file-hook
  ;       and recurse.
  (defun nogit-sync-if-configured ()
    (interactive)
    (save-match-data
      (if (and
           (buffer-file-name)
           (file-exists-p (format "%s/../.nogit" (buffer-file-name)))
           (not (boundp 'in-nogit-sync))
           )
          (let ((in-nogit-sync t))
           (message (substring (shell-command-to-string "nogit sync") 0 -1))
            (revert-buffer nil t)
            )
        )
      )
    )

  ; Arrange to run "nogit sync" when the user loads a nogit-controlled file,
  ; starts editing it for the first time, or saves it.
  (add-hook 'find-file-hook 'nogit-sync-if-configured)
  (add-hook 'first-change-hook 'nogit-sync-if-configured)
  (add-hook 'after-save-hook 'nogit-sync-if-configured)

Preparing git repositories for use with nogit
=============================================
If you're interested in setting up a parent and child repository for
use with nogit, there's almost nothing to it. In the child repository,
just put all of the files you want to be treated with nogit's
semantics. You don't need to fiddle with any .gitattributes or
merge=union configuration. The nogit clone will do everything
necessary for you so you get those semantics.

Then, in the parent repository, you'll simply want to augment your
.gitignore file to ignore all nogit-managed files from the child
repository as well as the ".nogit" directory itself.

Motivation
==========
I originally came up with nogit when I started maintaining a simple
TODO file for a project which had a code implementation split across
multiple code repositories. I was intentionally keeping my TODO file
outside of revision control to be lightweight in a couple of ways:

  1. Many TODO items required implementing a feature in multiple
     repositories (both client and server, say), so having a separate
     TODO file meant I didn't need to decide which repository to add
     the TODO file to. And I also didn't need to add the same entriy
     to TODO files in each of multiple repositories.

  2. TODO items are self-descriptive. Any commit message I might have
     written when adding a TODO item would be adequate as "Add <item>"
     and similarly for "Remove <item>" so there's inherently no
     advantage to commit messages for these changes.

Of course, a significant disadvantage of my approach was that my TODO
file was totally private. I was missing out on the collaborative
features that git provides.

So, nogit was conceived of as a way to keep my lightweight process of
maintaining the TODO file, (simply editing the file and doing nothing
more), while also allowing for distributed editing of the file.