Git for Plan 9: git/fs

Plan 9 is a non-posix system that currently has no git port.  Git
itself feels distinctly un-plan9ish.

Git/fs implements a git client for plan 9.  The intent is to support
working with git repositories, without cloning the git interface

Git/fs is alpha software. It more or less works for me, but has many
bugs, and many more missing tools, but it's at the point where the
hard parts are done, and "the rest is just scripting", using standard
command line tools (cp, echo, diff, patch, and diff3).


The git/fs program provides a file system mounted on /mnt/git.  It
provides a read-only view into the repository contents to allow
scripts to inspect the data.  Surrounding scripts and binaries will
manipulate the repository contents directly.  These changes will be
immediately mirrored in the file system.

Scripts will generally mount git/fs as needed to do
their work, but if you want to browse the repository
manually, run it yourself. You'll get `/mnt/git` mounted,
with the following contents:

	/mnt/git/object:	The objects in the repo.
	/mnt/git/branch:	The branches in the repo.
	/mnt/git/ctl:		A file showing the status of the repo.
				Currently, it only shows the current branch.
	/mnt/git/HEAD		An alias for the currently checked out
				commit directory.

Visible Differences

The most obvious difference is that Git's index is a bit boneheaded, so I'm
ignoring it.  The index doesn't affect the wire protocol, so this
isn't an interoperability issue, unless you share the same physical
repository on both Plan 9 and Unix.  If you do, expect them to disagree
about the files that have been modified in the working copy.

In fact, the entire concept of the staging area has been dropped, as
it's both confusing and clunky.  There are now only three states that
files can be in: 'untracked', 'dirty', and 'committed'.  Tracking is
done with empty files under .git/index9/{removed,tracked}/path/to/file.

It's implemented in Plan 9 flavor C, and provides tools for writing
repository contents, and a file system for read-only access, which
will mirror the current state of the repository.


Install with `mk install`.


Some usage examples:

	git/clone git://git.eigenstate.org/ori/mc.git
	cd subdir/name
	git/add foo.c
	diff bar.c /mnt/git/HEAD/

Commits are presented as directories with the following

	author:	A file containing the author name
	hash:	A file containing the commit hash
	parent:	A file containing the commit parents, one per line.
	msg:	A file containing the log message for that commit
	tree:	A directory containing a view of the repository.

So, for example:

	% ls /mnt/git/branch/heads/master
	% cat /mnt/git/branch/heads/master/hash

	# This is the same commit, with the same contents.
	% ls /mnt/git/object/7d539a7c08aba3f31b3913e0efef11c43ea9f9ef

	# what git/diff will hopefully do more concisely soon, filtering
	# out the non-git files.
	ape/diff -ur /mnt/git/branch/heads/master/tree .
	Only in .: .git
	Only in .: debug
	diff -ur /mnt/git/branch/heads/master/tree/fold.myr ./fold.myr
	--- /mnt/git/branch/heads/master/tree/fold.myr	Wed Dec 31 16:00:00 1969
	+++ ./fold.myr	Mon Apr  1 21:39:06 2019
	@@ -6,6 +6,8 @@
	 	const foldexpr : (e : expr# -> std.option(constval))
	+/* Look, diffing files just works, and I don't need any fancy glue! */
	 const foldexpr = {e
	 	match e
	 	| &(`Eident &[.sc=`Sclassenum, .name=name, .ty=`Tyenum &(`Body enum)]):
	Only in .: refs

The following utilities and binaries are provided:

	fs:	The git filesystem.
	fetch:	The protocol bits for getting data from a git server.
	send:	The protocol bits for sending data to a git server.
	save:	The gnarly bits for storing the files for a commit.
	conf:	A program to extract information from a config file.
	clone:	Clones a repository.
	commit:	Commits a snapshot of the working directory.
	log:	Prints the contents of a commmit log.
	add:	Tells the repository to add a file to the next commit.
	walk:	`du`, but for git status.

Supported protocols: git:// and git+ssh://. If someone
implements others, I'll gladly accept patches.


Documentation has not yet been written.  You'll need to read the
source. Notably missing functionality includes:

	git/mkpatch:	Generate a 'git am' compatible patch.
	git/apply:	Apply a diff.
	git/diff:	Wrapper wrapper around git/walk that
			diffs the changed files.
	git/merge:	Yup, what it says on the label. Should
			also be a script around git/fs.
	git/log:	Need to figure out how to make it filter
			by files.