Numpy SVN to Git conversion

We do Numpy SVN -> GIT conversion as listed below.

All of this is driven by a Makefile, whose targets we list below. Quick usage:

svnsync http://... numpy-svn make all SVN=numpy-svn

You also need an authors.map in the format

svnaccount Real Name <real@email.foo>

mapping SVN users to Git users. (We don't add it into this repository.)

export (step 1)

Use svn-all-fast-export to produce a Git repository.

We move all "undesired" crap under crud/ -- we don't drop anything in this stage.

We also include SVN metadata into the commit messages. This will be rewritten later on.

Valid SVN tags go, as branches, under svntags/.

verify (step 1.5)

Compute checksums for the contents of all revisions in SVN and in Git, and fail if the checksums do not match.

postprocess (step 2)

Generic postprocessing (postprocess.sh)

This entails a couple of things:

1. Merge point grafting.

   As is well-known, SVN history contains no merge information. So, we have to list the relevant info manually. This goes into numpy.grafts -- there we list the merge commits, and the extra parent of the merge commit.

   The point here is that the branches under crud/ will be hidden in the end. However, some of them were topic branches once in a time, so this would hide some relevant history. So here we aim to stitch the history manually together, by connecting the topical work to the trunk by manually inserting merge parents.

   What postprocess.sh essentially does here, is that it looks up the hash corresponding to the SVN revisions in the .grafts file, and dumps that information to Git via the text file info/grafts.

2. Hide all branches under crud/.

   This is done by relocating refs/heads/crud to refs/svn. This hides them from git branch.

   Such hidden refs can still be pushed and pulled, but they won't come along automatically -- refs/svn/*:refs/svn/* needs to be explicitly given to git push.

3. Convert all branches under svntags/ to real Git tags. The branches are removed, leaving only the tags.
4. git prune is called to get rid of unwanted stuff.
5. We check which SVN commits didn't make it into the Git repo, and dump that information to log-REPONAME-dropped.

6. SVN metadata is stripped from the commit messages.

   At the same time, this step makes the grafts permanent, and we can remove the info/grafts file.

final-cleanup (step 3)

We move a couple of leftover branches and tags under refs/svn.

gc (step 4)

Simply run git gc

graft (diagnostic)

When playing around with grafting, it's useful to just run make clean export first, and then do

• edit numpy.grafts
• run make graft

until the result is satisfactory.

branchstat (diagnostic)

The branchstat.sh script checks all remaining branches, and reports those with dangling unmerged commits.

It ignores the branches listed in numpy.branchskip