;;;;;
title: Setting up an ABCL mirror from SVN to Git
date: 2016-08-03 12:03:02
format: md
tags: git
;;;;;

## Copies of copies

As it so happens the ABCL main repository is held in Subversion, but since I'm
more productive with Git I usually use a conversion to Git via the `git-svn`
program.  I've based my own copy off of [slryus'
one](https://github.com/slyrus/abcl), however I had to fetch and update my own
local copy since neither of us had done any fetching in quite some time.  I'm
writing down some notes below to make sure I (or others) can repeat the process
in the future.

First we need a copy of an existing Git conversion.

    git clone https://github.com/Ferada/abcl.git abcl-git
    # or in case you have SSH access
    git clone git@github.com:Ferada/abcl.git abcl-git

The `master` branch should be a direct mirror of the SVN repository, i.e. only
have commits with `git-svn` annotations, like
`git-svn-id: http://abcl.org/svn/trunk/abcl@14851 1c010e3e-...`.

Next we want to initialise the SVN remote and fetch the new commits.

    git svn init --prefix=abcl/ http://abcl.org/svn/trunk/abcl
    git svn fetch -r 14791:14851

Note that the first revision in the `fetch` command is the last one in the Git
`master` branch and the other one is the current `HEAD` of the SVN repository.

This process will take just a few moments, however while all the new commits
will be based off of the `master` branch in Git, the first commit will be a
duplicate and have more changes than the existing commit in `Git`.

    2015-08-31 20:55 mevenson           │ │ o │ │ │ ansi-test: reference new git repository
    2015-07-01 04:16 mevenson           o─┴─│─┴─┴─┘ abcl-asdf: fix usage with local repository   <<<<
    2015-07-01 04:16 mevenson           │ I─┘ abcl-asdf: fix usage with local repository         <<<<
    2015-06-30 18:42 mevenson           o abcl-asdf: correct metadata

The newly created first commit (14791 here) has lots of changes.

    .dir-locals.el
    CHANGES
    COPYING
    MANUAL
    README
    abcl.asd
    abcl.bat.in
    ...

While the second, pre-existing one, has way less (and is just showing the same
changes that are in the SVN commit).

    contrib/abcl-asdf/abcl-asdf.asd
    contrib/abcl-asdf/abcl-asdf.lisp
    contrib/abcl-asdf/maven-embedder.lisp

To correct that and continue with a linear history I'm using the interactive
rebase command.

    git co -b test
    git reset --hard abcl/git-svn
    git rebase -i <commit _before_ the duplicated one>

Copy the hash of the correct, smaller commit and replace the `pick ...` line
(at the top) that contains the duplicated commit with the one from the
cloned-from Git repository, then exit the editor.  Once the rebase is done we
just need to update the ref for `git-svn`.

    git update-ref refs/remotes/abcl/git-svn test

Note the syntax.  If done correctly it will be updated in e.g. `tig`, if not
there'll be a *new* entry showing up in `git show-ref`.

Lastly we want to rebase `master` to get the new commits.

    git co master
    git co -D test
    git rebase abcl/git-svn master

Which will look somewhat like this:

    2016-06-13 08:06 mevenson           o [master] {abcl/git-svn} {github/master} doc: note changes for abcl-1.3.4
    2016-05-16 23:05 mevenson           o Update to asdf-3.1.7
    2016-05-16 21:43 mevenson           o Update to jna-4.2.2

And push the updates.

    git push origin master