Section 6.1. Source Control and Ant

6.1. Source Control and Ant

When you work in teams, you have to coordinate your efforts. That means discussing and planning, but even with the best of intentions, you can still end up with unintentional conflicts. You may have made some brilliant changes to the code, only to find them wiped out by mistake when another programmer uploads his own version of the same file.

Source control helps prevent these problems by controlling access to code and by maintaining a history of the changes made so things aren't destroyed unintentionally. Storing a history of your code is powerful; you can compare a new (buggy) file against an older one, and you can revert to a previous version in case things have gone bad.

Ant has several source control tasks, shown in Table 6-1.

Table 6-1. Source control tasks

Task name	Description
clearcase	Tasks for ClearCase cleartool checkin, checkout, uncheckout, update, lock, unlock, mklbtype, rmtype, mklabel, mkattr, mkdir, mkelem, and mkbl commands
Continuus/Synergy tasks	Tasks for Continuus ccmcheckin, ccmcheckout, ccmcheckintask, ccmreconfigure, and ccmcreateTask commands
cvs	Specifies how to work with packages and modules retrieved from a CVS repository
cvschangelog	Creates change reports from a CVS repository
cvspass	Adds entries to a .cvspass file
cvstagdiff	Creates an XML-formatted report of the changes between two tags or dates recorded in a CVS repository
Microsoft Visual Sourcesafe tasks	Tasks for Visual SourceSafe vssget, vsslabel, vsshistory, vsscheckin, vsscheckout, vssadd, vsscp, and vsscreate commands
perforce	Tasks for Perforce p4sync, p4change, p4edit, p4submit, p4have, p4label, p4counter, p4reopen, p4revert, and p4add commands
pvcs	Retrieves and handles source code from a PVCS repository
sourceoffsite	Tasks for SourceOffSite sosget, soslabel, soscheckin, and soscheckout commands
starteam	Tasks for StarTeam stcheckout, stcheckin, stlabel, and stlist commands

Though Ant lets you work with various source control systems, most of its support revolves around CVS, which is used throughout this chapter. CVS is an open source project that started as a set of Unix shell scripts in 1986 and came into its own with dedicated software in 1989. Support for CVS is available on many operating systems: Unix, Linux, Windows, Mac, and others. For the full CVS story, look at http://www.cvshome.org.

To work with CVS using Ant, you need access to a CVS server. Most Linux and Unix installations come with a built-in CVS server. To test if you have a working CVS installation, type cvs --help at the prompt; you should see a list of help items. If you can't find a CVS server, you can download what you need from http://www.cvshome.org. Many CVS servers are available for Windows, such as CVSNT, available for free from http://www.cvsnt.org. To install CVSNT, download the executable file and run it.

The idea behind CVS, as with any repository software, is to manage and record changes to source code. What corresponds to a project for Ant is a module in CVS. Modules are represented by directories in CVS; the files you share are stored in the CVS repository. When you retrieve a file from the repository, you check the file out. After you've modified the file, you commit the file, checking it back in and sending those changes to the repository. If you want to refresh your own copy of a file, you update it from the repository.

Because each file must be independently tracked, CVS gives the individual files a version number automatically. Each time a file is committed, its version number is incremented. When you commit files to the repository, they'll get a new version number as well.

Using the cvs task, you communicate with the CVS server using CVS commands, which appear in Table 6-2.

Read more about these commands in the CVS guide at https://www.cvshome.org/docs/manual/cvs-1.11.7/cvs_16.html.

Table 6-2. CVS commands

CVS command	Does this
add	Specifies you want to add a new file or directory to the CVS repository
admin	Lets you work with administrative commands
annotate	Specifies the revision where each line was modified
authserver	Specifies authentication mode for the server
chacl	Specifies the access list for a directory
checkout	Checks out source code from the repository
chown	Changes the owner of a directory in the repository
commit	Checks source code files into the repository
diff	Displays the differences between source code revisions
edit	Specifies you want to edit a file
editors	Specifies you want to watch who has been editing a particular file
export	Exports source code from a CVS repository (similar to checkout)
history	Displays the CVS repository access history
import	Imports source code into a CVS repository
info	Displays information about the CVS repository and its supported protocols
init	Creates a CVS repository and initializes it
log	Displays information on file history
login	Asks for a password, if needed
logout	Logs out of a server
ls	Lists the files in the CVS repository
lsacl	Lists the CVS directories access control list
passwd	Sets a user's CVS password
rannotate	Displays the revision in which source lines were modified
rdiff	Creates patch files by comparing two files and outputting a file that be used to update one into the other
release	Specifies that a module will not be used anymore
remove	Removes an item from a CVS repository
rlog	Displays CVS history information for a module
rtag	Adds a tag to a CVS module
server	Lets you set server modes for access
status	Displays checked-out file information
tag	Adds a tag to checked-out files
unedit	Undoes an edit command that's been executed
update	Updates local copies of a file with those in the CVS repository
version	Shows the CVS version
watch	Watches a file or files
watchers	Displays which users are watching a file or files

The first step in working with CVS is to log into the CVS server, typically done with the cvspass task.