# GF Darcs repository

Author: Björn Bringert <bringert@cs.chalmers.se>
Last update: Wed Oct 3 15:13:24 2007

- What is darcs?
- How do I install Darcs?
- Read-only access
  - Getting a fresh copy for read-only access
  - Updating your copy
  - Recording local changes
  - Submitting patches
- Read-write access
  - Setting up your $PATH on the Chalmers system
  - Getting a fresh copy
  - Getting other people's changes?
  - Commit your changes
  - Apply a patch from someone else
- Troubleshooting
  - I get the error "darcs not found" when pushing
  - I get the error "(sftp) failed to fetch files."
  - How do I avoid typing in my password so many times?
    - Using ssh ControlMaster
    - Using ssh-agent
- Technical Information
- Further information about Darcs

GF has now been moved to a Darcs repository. No changes should be committed to the CVS repository from now on.

# What is darcs?

Darcs is a decentralized revision control system. These are some of the reasons for switching GF from CVS to Darcs:

- You can keep local revision control in your checked-out copy, since each checked-out copy is a repository in itself. For example, this allows the WebALT project to keep a local GF repository for working on the resource grammars, and submit patches to the main repo when that is convenient. It also allows individual developers to keep revision control over their own modifications before they are ready to submit them, or if they are temporarily without net access.

- We can provide read-only access over HTTP using the existing CS web server.

- It is possible and easy to rename and remove both files and directories.

For more information about Darcs, see http://darcs.net/.

# How do I install Darcs?

There are precompiled packages for many platforms available at http://darcs.net/DarcsWiki/CategoryBinaries.

There is also source code if you want to compile it yourself. Darcs is written in Haskell and you need GHC to compile it.

# Read-only access

## Getting a fresh copy for read-only access

Anyone can get the latest development version of GF by running (all on one line):

      $ darcs get --partial --set-scripts-executable http://www.cs.chalmers.se/Cs/Research/Language-technology/darcs/GF/

This will create a directory called `GF` in the current directory. See `GF/src/INSTALL` for instructions on compiling. The main difference compared to compiling a GF release is that you need to run `autoconf` before `./configure`.

## Updating your copy

To get all new patches from the main repo:

      $ darcs pull -a

This can be done anywhere in your local repository, i.e. in the `GF` directory, or any of its subdirectories.

Without `-a`, you can choose which patches you want to get.

## Recording local changes

Since every copy is a repository, you can have local version control of your changes.

If you have added files, you first need to tell your local repository to keep them under revision control:

      $ darcs add file1 file2 ...

To record changes, use:

      $ darcs record

This creates a patch against the previous version and stores it in your local repository. You can record any number of changesets before pushing them to the main repo. In fact, you don't have to push them at all if you want to keep the changes only in your local repo.

If you think there are too many questions about what to record, you can use the `-a` flag to `record`. Or answer `a` to the first question. Both of these record all the changes you have in your local repository.

## Submitting patches

If you are using read-only access, send your patches by email to someone with write-access. First record your changes in your local repository, as described above. You can send any number of recorded patches as one patch bundle. You create the patch bundle with:

      $ darcs send -o mypatch.patch
      $ gzip mypatch.patch

(where `mypatch` is hopefully replaced by a slightly more descriptive name). Since some e-mail setups change text attachments (most likely by changing the newline characters) you need to send the patch in some compressed format, such as GZIP, BZIP2 or ZIP.

Send it as an e-mail attachment. If you have sendmail or something equivalent installed, it is possible to send the patch directly from darcs. If so, replace `-o mypatch.patch` with `--to=EMAIL` where `EMAIL` is the address to send it to.

# Read-write access

If you have an account on the Chalmers system and want read-write access, you can access the repository using ssh. You need to be a member of the `langtech` group to push changes to the repository.

If darcs seems to ask for your password multiple times for a single push or pull, try upgrading to recent versions of darcs and OpenSSH (OpenSSH version 4 or newer). Recent OpenSSH versions include a connection multiplexing feature, which recent darcs versions support. Note that darcs 1.0.9 has some problems with this, try downgrading to darcs 1.0.8.

Note: we seem to have some problems getting read-write access working smoothly on Windows. If you figure out how to do this, let us know. If not, you can still use read-only access, record patches in your local repository, and send them by e-mail once in a while.

## Setting up your $PATH on the Chalmers system

The `darcs` program has to be on your `$PATH` on the Chalmers system to make it possible for you to push changes to the main repository. To fix this, log in to your Chalmers account and run:

      mkdir -p $HOME/.vcs4
      echo unsup >> $HOME/.vcs4/pathsetup

Note that the path setup works differently on different Chalmers machines. The command above will setup you path on the newer machines correctly.

## Getting a fresh copy

Get your copy with (all on one line), replacing `bringert` with your own username on the Chalmers system:

      $ darcs get --partial --set-scripts-executable bringert@momo.medic.chalmers.se:/users/cs/www/Research/Language-technology/darcs/GF/

Note that you really need to use `momo.medic.chalmers.se` (or some other server with the new Linux system) since we need to have a server with at least Darcs 1.0.4. If you use some server with an earlier Darcs version you can mess up the repository.

The option `--partial` means that you do not download all of the history for the repository. This saves space, bandwidth and CPU time, and most people don't need the full history of all changes in the past.

## Getting other people's changes?

Get all new patches from the main repo:

      $ darcs pull -a

Without `-a`, you can choose which patches you want to get.

## Commit your changes

There are two steps to commiting a change to the main repo. First you have to record the changes that you want to commit, then you push them to the main repo.

For instructions on recording your changes locally, see "Recording local changes" above.

Then you can push the patch(es) to the main repo. If you are using ssh-access, all you need to do is:

      $ darcs push

If you use the `-a` flag to push, all local patches which are not in the main repo are pushed.

## Apply a patch from someone else

Use:

      $ darcs apply < mypatch.patch

This applies the patch to your local repository. To commit it to the main repo, use `darcs push`.

# Troubleshooting

## I get the error "darcs not found" when pushing

If you get `darcs not found` when you try to push your changes, you don't have darcs on your `$PATH` on the Chalmers system. See the section above on setting up your `$PATH` on the Chalmers system.

## I get the error "(sftp) failed to fetch files."

There seems to be a problem with how darcs 1.0.4 calls sftp, which means that normal password authentication does not work. Try upgrading to a more recent version of darcs.

## How do I avoid typing in my password so many times?

### Using ssh ControlMaster

Get a recent darcs and OpenSSH, see above.

Note that the ControlMaster feature does not seem to work properly in darcs 1.0.9 under Mac OS X. Use darcs 1.0.8 instead.

### Using ssh-agent

NOTE: the method below will not work with `momo.medic.chalmers.se`. MEDIC has decided to disable public key authentication on all new machines. This section is included just for reference in case they decide to enable it again.

With the ssh access method, Darcs needs to log in with ssh. For some reason it needs to do this several times for each operation. You can avoid this by setting up public-key authentication for ssh.

Here is a guide to setting this up: http://cfm.gs.washington.edu/security/ssh/client-pkauth/

Short summary (should on most modern Linux distros, maybe other platforms too):

Generate a key pair:

      $ mkdir -p ~/.ssh
      $ chmod 700 ~/.ssh
      $ ssh-keygen -q -f ~/.ssh/id_rsa -t rsa
      Enter passphrase (empty for no passphrase): ...
      Enter same passphrase again: ...

Upload the public key to your Chalmers account (replace `bringert` with your username):

      $ ssh-copy-id -i ~/.ssh/id_rsa.pub bringert@remote.cs.chalmers.se

Add the key to ssh-agent (ssh-agent then remembers your key for a while, so that you don't have to type in the passphrase again):

      $ ssh-add
      Enter passphrase for /home/bjorn/.ssh/id_rsa: ...

This is the part that is most likely to fail. If ssh-add says that it couldn't find ssh-agent, you need to follow the instructions linked to above to start ssh-agent.

Try to use it to log in (with your own username again):

      $ ssh bringert@remote.cs.chalmers.se
      ...
      zsh:bringert:[~]>

# Technical Information

This section contains information about how the repository is set up. It might be useful for troubleshooting the repository setup or creating a similiar setup for another repository.

The main repository is in `/users/cs/www/Research/Language-technology/darcs/GF`, which is visible to the web server. The repository and all files and directories in it group writable, owned by the group `langtech`, and all directories have the setgid bit set:

      drwxrwsr-x  10 bringert langtech 512 Nov 17 19:00 /users/cs/www/Research/Language-technology/darcs/GF

The repo has this in `_darcs/prefs/defaults`:

      apply posthook find . -user "$USER" -a ! -perm +g+w -exec chmod g+w '{}' ';'
      apply run-posthook

The server which we push to has darcs 1.0.4, which is needed for posthook support.

# Further information about Darcs

For more info about what you can do with darcs, see http://darcs.net/manual/