GF Darcs repository
Author: Björn Bringert <bringert@cs.chalmers.se>
Last update: %%date(%c)

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**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 to compiling a GF release from sources 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. To record some changes, use:

```
$ darcs record
```

This creates a patch against the previous version and stores it 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.

**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.

== Setting up ssh alias and ControlMaster ==

In order to avoid typing in you password multiple times for each
action on the remote repository, you can use ssh's ControlMaster
functionality. This allows several ssh instances to use the connection
established by one existing instance.

**NOTE: You need OpenSSH version 4 or newer for this to work.** You
can check your OpenSSH version with ``ssh -V``. If you have an older
version of OpenSSH, you need to remove the ControlPath line below,
and you can skip the "Setting up an ssh ControlMaster connection"
step. You will be typing in your password a lot...


Add this to ``~/.ssh/config`` (create the file if it does not exist,
replace ``bringert`` with your own username on the
Chalmers system):

```
Host gfreposerver
HostName momo.medic.chalmers.se
User bringert
ControlPath /tmp/ssh-gfreposerver
```

This sets up an alias ``gfreposerver`` for the server we use 
for the Darcs repository. 
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 Darcs 1.0.4. If you use some server with an earlier Darcs version you can mess up the repository.

More information about the ControlMaster feature is available in 
``man ssh_config``.


== Setting up an ssh ControlMaster connection ==

Before connecting to the remote server, you need to set up a master
ssh connection to it. As long as this connection is up, you don't
need to enter your password when connecting to the GF repository server.

Start the master connection:

```
$ ssh -M gfreposerver
```

This looks just like a normal ssh login, and you get a shell on the server.
Put this connection in the background, or keep it open in a window
somewhere.

**NOTE: You need to have a ControlMaster connection running whenever you want to access the repo using ssh.**
You may want to create a script or alias for starting the connection.

=== Automating the ControlMaster connection ===

You can use a darcs wrapper which sets up a ControlMaster connection
if there isn't one already. Put the script [darcs-cm darcs-cm]
somewhere on your path and use it instead of ``darcs`` to work with 
the remote repository.

== Getting a fresh copy ==

Get your copy with (all on one line):

```
$ darcs get --partial --set-scripts-executable gfreposerver:/users/cs/www/Research/Language-technology/darcs/GF/
```

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:

```
$ 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.

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. Either use
Darcs 1.0.3 on your client, and be prepared to enter your password
many times, or use the ssh ControlMaster feature as described above.

== I get the error "Not a repository: gfreposerver:..." ==

You get this error when you have set up ControlMaster, but don't have a master
connection running. Start a master connection:

```
$ ssh -M gfreposerver
```

or use the ``darcs-cm`` script shown above.

== I'm using Cygwin and I get "mm_receive_fd: no fd" ==

It seems like ssh connection multiplexing doesn't work under Cygwin:
http://www.mail-archive.com/cygwin@cygwin.com/msg61323.html.

The workaround is to use password authentication. Just remove the
ControlPath line in ``.ssh/config``, and don't setup a ControlMaster
connection (and don't use darcs-cm).

You should then be able to checkout using just:

```
$ darcs get --partial --set-scripts-executable gfreposerver:/users/cs/www/Research/Language-technology/darcs/GF/
```

The problem is that when you pull and push, you have to enter your
password quite a few times.


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

=== Using ssh ControlMaster ===

See above.


=== 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/


