Requirements for integrating a new git subcommand

I have completed work on git-weave (the tool I had called 'gitpacker' in some previous postings). I want to submit a patch that integrates it into git; in hopes of smoothing the process I have some technical and procedural questions.

First, however, let me present the git-weave documentation for design review:

---------------------------------------------------------------------- git-weave(1) ============

NAME ---- git-weave - Weave a sequence of trees and log data into a repository

SYNOPSIS -------- [verse] 'git-weave' [-v] [-m limit] [-q] indir outdir

DESCRIPTION ----------- git-weave accepts an input directory containing a sequence of subdirectories and a metadata file, and composes them into a git repository created under the specified output directory (which must not exist).

If the input directory is identifiably a git repository, the weave operation is reversed; tree states from each commit are unraveled into the output directory with a log holding commit metadata (committer/author/comment information and parent headers representing links of the repository DAG) and tags.

This tool is primarily intended for importing and working with project histories that have been preserved only as linear sequences of release snapshots. It may also be useful for surgery on linear repositories

While the weave operation can build a commit graph with any structure desired, an important restriction of the inverse (unraveling) operation is that it operates on *master branches only*. The unravel operation discards non-master-branch content, emitting a warning to standard error when it has to do so.

Commits from the repository's master branch are unraveled into directories named for integers from 1 increasing, but their order of composition when re-woven is actually set by the sequence of entries in the metadata file. File trees may be inserted or removed without hindering re-weaving provided the pointers in the log's parent fields are fixed up properly.

METADATA FILE FORMAT -------------------- The metadata file format will contain three kinds of stanzas: entries for commits, entries for lightweight tags, and entries for annotated tags.

A commit stanza has headers similar to those in a commit raw log: commit, committer, author, and optionally parent headers. The header contents are not hash IDs, but arbitrary text cookies either declared by a previous commit stanza or referencing one. The following example declares "8" to be a commit ID, and references a previous commit identified as '7'. Note that commit IDs are not required to be numeric strings, though the unravel operation generates them that way.

------------ commit 8 parent 7 author Eric S. Raymond <esr@thyrsus.com> 1325026869 +0000 committer Eric S. Raymond <esr@thyrsus.com> 1325026869 +0000

Initial revision . ------------

The text body of a commit comment or tag comment entry is delimited from the headers by an empty line; the text body must always end with "." on a line by itself; and text lines beginning with "." will have an additional "." prepended to them.

A commit stanza may also have a "directory" header. If present, this sets the name of the subdirectory in which git-weave expects to find the content tree for this commit. For example

------------ commit 24 directory intercal-0.17 parent 23 author Eric S. Raymond <esr@thyrsus.com> 1325026489 +0000 committer Eric S. Raymond <esr@thyrsus.com> 1325026489 +0000

The state of the INTERCAL project at release 0.17. . ------------

A label stanza declares a lightweight tag. This example declares a tag 'sample' pointing at the commit identified as 102.

------------ label sample refers-to 102 ------------

A tag stanza declares an annotated tag. This one declares a tag named 'annotated1' pointing at the commit declared as 99.

------------ tag annotated1 refers-to 99 tagger Eric S. Raymond <esr@thyrsus.com> Sat Nov 17 03:16:26 2012 -0500

This is an example annotated tag. . ------------

When you are composing commit and tag stanzas by hand, you can count on any of the date formats normally acceptable to git to be recognized.

If, when weaving, any committer or author or tagger line, the date is omitted, git-weave will supply as a default the latest modification time of any file in the corresponding tree.

If a committer or author or tagger line is omitted entirely, the user's name and email address as retrieved by ''git-config'' will be supplied as defaults, and the date will default as above.

Thus, the following variation on one of the previous examples is a valid stanza:

------------ commit 24 directory intercal-0.17 parent 23

The state of the INTERCAL project at release 0.17. . ------------

OPTIONS
-------
-q::
	Be quiet.  Suppress the normal spinning-baton progress meter
	with timing information.

-m::
	Limit the number of commits or trees processed to a specified
	integer maximum. '0' means process all of them.

-v::
	Be verbose, enabling progress and command-execution messages
	This option will probably be of interest only to developers;
	consult the source code for details.

EXAMPLES
--------
* Weave a sequence of trees in the directory 'unraveled' 
into a git repository in the directory 'repo'. 
+
------------
$ rm -fr repo; git-weave unraveled repo
------------
+
The metadata is expected to be in 'unraveled/log'.  This mode of
operation is triggered when there is no file 'unraveled/.git', 

* Unravel a repository in the directory 'repo' into a sequence
of file trees and a metadata log in the directory 'unraveled'.
+
------------
$ rm -fr unraveled; git-weave repo unraveled
------------
+
This mode of operation is triggered when there is a 'repo/.git' file.

SEE ALSO -------- linkgit:git-log[1] linkgit:git-checkout[1] linkgit:git-add[1] linkgit:git-mktree[1] linkgit:git-ls-tree[1] linkgit:git-update-references[1]

GIT --- Not yet part of the linkgit:git[1] suite ----------------------------------------------------------------------

Yes, there are scripts in contrib that do similar things. git-weave is an improvement is several ways: (a) it is documented, (b) I am shipping it with a functional test, (c) I am prepared to maintain it and am quite unlikely to drop out of sight :-), (d) it does both the import operation *and its inverse*, and (e) it is rather more powerful, including the ability to decorate the import with annotated tags.

Now *my* questions:

1. I have a round-trip test for the tool that I can very easily adapt
to speak TAP.  To function, the test will require a small linear
history to operate on in the form of an import-stream file (so the
result of round-tripping through a weave-unravel can be diffed against
the original).  Does the distribution include any test repos?  If
so, where can I find them?

2. I understand that a "git foo" command is typically implemented
as "git-foo" binary or script in /usr/lib/git-core.  What I don't
know is what the other interfacing requirements are.  Are they
documented anywhere?  In particular...

3. Is there any registration protocol other than simply installing 
the extension in the subcommand library?

4. How does "git help" work?  That is, how is a subcommand expected
to know when it is being called to export its help text?

5. I don't see any extensions written in Python.  Are there any special
requirements or exclusions for Python scripts?