FP Tools CVS Cheat Sheet

At Glasgow, we use CVS (Concurrent Version System) to keep track of our sources for various software projects. CVS lets several people work on the same software at the same time, allowing changes to be checked in incrementally.

Information on using CVS can be obtained from Cyclic Software. If you're at Glasgow, the full documentation for CVS is online, in info format (use 'info cvs' or run emacs and type C-h i). A good source of tips is the CVS FAQ, in /local/doc/gnu/CVS.FAQ. Bradley C. Kuszmaul also provides a "to the point" introduction to CVS.

This note is supposed to be a set of guidelines for how to use our CVS repository, and will probably evolve in time. The main thing to remember is that most mistakes can be undone, but if there's anything you're not sure about feel free to bug the local CVS meister (namely Simon Marlow).

Contents

• Read-only remote access
• Read-write remote access
• Using CVS for the first time
• Checking out a source tree
• Committing changes
• Updating your source tree
• General Hints

Remote Read-only CVS Access

Read-only access is available to anyone - there's no need to ask us first. We use the anoncvs mechanism pioneered by the OpenBSD folks. To get read-only access to our repository, just set your CVSROOT environment variable to

	anoncvs@solander.dcs.gla.ac.uk:/cvs

and you can then check out a source tree using normal CVS commands. For example:

	$ cvs checkout fpconfig
	$ cd fptools
	$ cvs checkout ghc

gets a brand spanking new set of GHC sources. The layout of our CVS repository is described below, under Using CVS for the first time.

With read-only CVS access you can do anything except commit changes to the repository. You can make changes to your local tree, and still use CVS's merge facility to keep your tree up to date, and you can generate patches using 'cvs diff' in order to send to us for inclusion.

If you like, you can use ssh instead of the standard rsh to connect to the CVS server. Just set your CVS_RSH variable to ssh.

Remote Read-Write CVS Access

We generally supply read-write access to folk doing serious development on some part of the source tree, when going through us would be a pain. If you're developing some feature, or think you have the time and inclination to fix bugs in our sources, feel free to ask for read-write access. There is a certain amount of responsibility that goes with commit privileges; we are more likely to grant you access if you've demonstrated your competence by sending us patches via mail in the past.

To use remote CVS, you need to supply me with a username and encrypted password. Once you've done that and the account has been set up, you need to do:

     cvs -d <username>@solander.dcs.gla.ac.uk:/local/fp/src/cvsroot login

CVS will ask for a password. You only need to enter the password once, it will be recorded in .cvspass in your home directory.

   setenv CVSROOT :pserver:<username>@solander.dcs.gla.ac.uk:/local/fp/src/cvsroot

The CVSROOT environment variable will be recorded in the checked-out tree, so you don't need to set this every time either. Ignore the instructions for setting CVSROOT below.

Using CVS for the First Time

• ok, everybody now...) Firstly, identify which areas of the source tree you'll be working on. The directory structure looks like this:

  fptools/ghc	GHC
  fptools/happy	Happy
  fptools/haggis	Haggis
  fptools/green-card	Green Card
  fptools/nofib	Nofib test suite
  fptools/hdirect	IDL-to-Haskell compiler
  fptools/common-rts	GHC/Hugs combined run-time system

  For each directory, there's a mailing list: fp-cvs-ghc, fp-cvs-nofib etc. Everyone on the mailing list is sent a message automatically by CVS whenever someone checks in a change, this helps to keep track of what's going on when several people are working on related stuff. Ask the CVS meister to put you on the relevant mailing lists.

• Create a .cvsrc file. Mine looks like this:

  	checkout -P
  	release -d
  	update -P
  	diff -c
  

  It just gives default flags for some of the CVS commands. For instance, the -P flag to 'checkout' says prune empty directories, which is normally what you want.

Checking Out a Source Tree

• Check out your sources. If you're not at Glasgow, make sure you set your CVSROOT environment variable according to either of the remote methods above. Glasgow folk need to set their CVSROOT environment variables as follows:

  	$ CVSROOT=/local/fp/src/cvsroot
  	$ export CVSROOT
  

  or, if you're using csh or tcsh:

  	$ setenv CVSROOT=/local/fp/src/cvsroot
  

  The Approved Way (at least by me) to check out a source tree is as follows:

  	$ cvs checkout fpconfig
  

  At this point you have a new directory called 'fptools' which contains the basic stuff for the fptools suite - including the configuration files and some other junk.

  	$ mv fptools <directory>
  

  You can call the fptools directory whatever you like, CVS won't mind.

  	$ cd <directory>
  	$ cvs checkout ghc happy
  

  The second command here checks out the relevant modules you want to work on. For a GHC build, for instance, you need at least the ghc module (in fact you can get away with just that).

Committing Your Changes

This is only if you have read-write access to the repository. For anoncvs users, CVS will issue a "read-only repository" error if you try to commit changes.

• Build the software, if necessary. Unless you're just working on documentation, you'll probably want to build the software in order to test any changes you make. For GHC, instructions can be found in the GHC installation guide.

• Make changes. Preferably small ones first.

• Test them. You can see exactly what changes you've made by using the cvs diff command. For example,

  	$ cvs diff
  

  lists all the changes (using the diff command) in and below the current directory. In emacs, C-c C-v C-= runs cvs diff on the current buffer and shows you the results.

• Before checking in a change, you need to update your source tree:

  	$ cd fptools
  	$ cvs update
  

  This pulls in any changes that other people have made, and merges them with yours. If there are any conflicts, CVS will tell you, and you'll have to resolve them before you can check your changes in. The documentation describes what to do in the event of a conflict.

  It's not always necessary to do a full cvs update before checking in a change, since CVS will always tell you if you try to check in a file that someone else has changed. However, you should still update at regular intervals to avoid making changes that don't work in conjuction with changes that someone else made. Keeping an eye on what goes by on the mailing list can help here.

• When you're happy that your change isn't going to break anything, check it in. For a one-file change:

  	$ cvs commit <filename>
  

  CVS will then pop up an editor for you to enter a "commit message", this is just a short description of what your change does, and will be kept in the history of the file.

  If you're using emacs, simply load up the file into a buffer and type C-x C-q, and emacs will prompt for a commit message and then check in the file for you.

  For a multiple-file change, things are a bit trickier. There are several ways to do this, but this is the way I find easiest. First type the commit message into a temporary file. Then either

  	$ cvs commit -F <commit-message> <file_1> .... <file_n>
  

  or, if nothing else has changed in this part of the source tree,

  	$ cvs commit -F <commit-message> <directory>
  

  where <directory> is a common parent directory for all your changes, and <commit-message> is the name of the file containing the commit message.

  Shortly afterwards, you'll get some mail from the relevant mailing list saying which files changed, and giving the commit message. For a multiple-file change, you should still get only *one* message.

Updating Your Source Tree

It can be tempting to cvs update just part of a source tree to bring in some changes that someone else has made, or before committing your own changes. This is NOT RECOMMENDED! Quite often changes in one part of the tree are dependent on changes in another part of the tree (the mk/*.mk files are a good example where problems crop up quite often). Having an inconsistent tree is a major cause of headaches.

So, to avoid a lot of hassle, follow this recipe for updating your tree:

$ cd fptools
$ cvs update -Pd 2>&1 | tee log

Look at the log file, and fix any conflicts (denoted by a 'C' in the first column). If you're using multiple build trees, then for every build tree you have pointing at this source tree, you need to update the links in case any new files have appeared:

$ cd <build-tree>
$ lndir <source-tree>

Some files might have been removed, so you need to remove the links pointing to these non-existent files:

$ find . -xtype l -exec rm '{}' \;

And finally, re-configure to take into accound any changes in mk/config.mk.in.

$ ./configure

To be *really* safe, you should do

$ gmake boot && gmake all

from the top-level, to update the dependencies and build any changed files.

General Hints

• As a general rule: commit changes in small units, preferably addressing one issue or implementing a single feature. Provide a descriptive log message so that the repository records exactly which changes were required to implement a given feature/fix a bug. I've found this *very* useful in the past for finding out when a particular bug was introduced: you can just wind back the CVS tree until the bug disappears.

• Keep the sources at least *buildable* at any given time. No doubt bugs will creep in, but it's quite easy to ensure that any change made at least leaves the tree in a buildable state. We do nightly builds of GHC to keep an eye on what things work/don't work each day and how we're doing in relation to previous verions. This idea is truely wrecked if the compiler won't build in the first place!

• To check out extra bits into an already-checked-out tree, use the following procedure. Suppose you have a checked-out fptools tree containing just ghc, and you want to add nofib to it:

  	cd fptools
  	cvs checkout nofib
  

  or:

  	cd fptools
  	cvs update -d nofib
  

  (the -d flag tells update to create a new directory). If you just want part of the nofib suite, you can do

  	cd fptools
  	cvs checkout nofib/spectral
  

  This works because nofib is a module in its own right, and spectral is a subdirectory of the nofib module. The path argument to checkout must always start with a module name. There's no equivalent form of this command using update.

Simon Marlow