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<h1>Branching with Eclipse and CVS, Part 1: The Basics</h1>
<div class="summary">
<h2>Summary</h2>
<p>This article presents a brief branch-and-merge scenario designed
to quickly illustrate some branch-and-merge features of Eclipse's CVS
support. We assume the reader already appreciates the value of branching
and merging in a source control environment. This article walks through
a step-by-step scenario illustrating simple branch-and-merge operations
using Eclipse-based IDEs with CVS as the source control mechanism.</p>
<p>For a branch-and-merge scenario that incorporates rebasing,
please refer to <a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html">Part 2</a> of this article. This
article is <b>not</b> a prerequisite for Part 2. Rather, Part 1 provides
simpler branch-and-merge techniques.</p>
<div class="author">By Paul Glezen, IBM and James Neethling</div>
<div class="copyright">Copyright &copy; 2007 IBM</div>
<div class="date">September 5, 2007</div>
</div>
<div class="content">
<h2>Introduction</h2>
In any source control management (SCM) environment, branching is a
powerful mechanism for controlled isolation. Despite being a simple
concept, controlled isolation is often avoided in practice because of
its implementation complexities. This article demonstrates how to
perform branching with Eclipse's CVS support. The Eclipse on-line
documentation covers this topic, but does not provide an end-to-end
scenario. The intended audience is software development professionals
with an appreciation for the roles of branch and merge techniques in
SCM.
<p>This article will employ a scenario of two programmers, Paul and
Wing, working on separate branches of the same project. Paul will branch
off main and modify some files while Wing continues to work on the main
branch, also modifying files. Paul will then merge his branch back to
the main branch. In doing so, Paul will address the resulting merge
conflicts. This flow is diagrammed below in the <a href="#scenario">Scenario
Diagram</a>.</p>
<p>The process is repeated for a second iteration to demonstrate the
so-called <b>merge-again</b> scenario. Work continues on the branch
after the first merge; then the branch is merged again later. The
merge-again scenario requires that you keep track of when you last
merged via tags. This will be demonstrated later in this article.</p>
<p>The <i><a name="scenario">Scenario Diagram</a></i> below will be
referenced throughout this article.</p>
<center><img src="images/scenario1.jpg"
alt="Elementary Branch Concept"></center>
<p><a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html">Part 2</a> of this article adds the <i>rebase</i>
operation to the scenario.</p>
<h2>Setup</h2>
The sample will use a few text files inside a simple project. In order
to carry out the sample yourself, you should already have a working
connection to a CVS repository in your Eclipse workspace.
<p>If possible, you should considering creating a new repository for
this scenario. That's because tags and branches are the central theme of
this article. And unlike files in a CVS repository, the tag and branch
metadata are difficult to selectively remove if you want to start over.
It's much easier to just wipe-out the repository and start with a new
one. If you do create your own CVS repository for this article, see the
<a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html#trouble">Troubleshooting section in Part 2</a>
for setting the necessary permissions on a new CVS repository.</p>
<p>The setup instructions below can be expedited through importing
the <a href="brtest.zip">brtest.zip</a> into a simple project <b>brtest</b>.
</p>
<ol type="1">
<li>Create a new simple project called <b>brtest</b>.</li>
<li>Add a new file called <code>f1.txt</code>. Add the following
contents.
<table border="1">
<tbody>
<tr>
<td><pre>This file will only be edited by Paul
This line will be changed later.
This line will be changed after the first merge.
The rest of this file will remain the same.<br></pre></td>
</tr>
</tbody>
</table>
</li>
<li>Add a file called <code>f2.txt</code> with the following
contents.
<table border="1">
<tbody>
<tr>
<td><pre>This file will only be edited by Wing.
This line will be changed later.
This line will be changed after the first merge.
The rest of this file will remain the same.</pre></td>
</tr>
</tbody>
</table>
</li>
<li>Add a file called <code>f3trivial.txt</code> with the
following contents.
<table border="1">
<tbody>
<tr>
<td><pre>This file will be edited by Paul and Wing.
This line will be changed by Paul only.
This line will be changed by Paul only after the first merge.
This line will be left alone.
This line will be changed by Wing only.
This line will be changed by Wing only after the first merge.
The rest of this file will remain the same.</pre></td>
</tr>
</tbody>
</table>
</li>
<li>Add a file called <code>f4conflict.txt</code> with the
following contents.
<table border="1">
<tbody>
<tr>
<td><pre>This file will be edited by Paul and Wing.
This line will be changed by both Paul and Wing.
This line will be changed by both Paul and Wing after the first merge.
The rest of this file will remain the same.</pre></td>
</tr>
</tbody>
</table>
<p>After adding the above files to your project and checking them
into CVS, your resource view should look something like the screen shot
below.</p>
<br>
<img alt="Checked in project" src="images/checked_in_project.jpg"><br>
</li>
</ol>
This sets up the environment for Paul. Wing will work in her own
workspace by retrieving the files from source control. For steps on
setting up a new project with source control, see the following section
in the Eclipse documentation: <b>Workbench User's Guide &rarr; Tasks
&rarr; Working in the team environment with CVS &rarr; Working with
projects shared with CVS</b>.
<h2>Merge Method</h2>
When branching off a development stream, it is often advisable to rebase
before merging the subbranch back to the main branch. To <b>rebase</b>
means to merge the contents of the main branch to the subbranch. If any
conflicts are to be resolved, they are done on the subbranch rather than
the main branch. If the merge goes well, the subbranch is merged to the
main branch. After having previously resolved all merge conflicts, this
last merge would be a trivial one. The advantages of taking the extra
rebase step is that it avoids having conflicts on the main branch and it
keeps the subbranch synchronized with the main branch. This is the
approach taken in <a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html">Part 2</a>.
<p>In this article, our primary focus is the merge mechanism of
Eclipse's CVS support, not the particular branching strategy. So here in
Part 1, we stick with the branch method illustrated in the <a
href="#scenario">Scenario Diagram</a>.</p>
<h2>Creating the Branch</h2>
At this point, Paul and Wing have the same version of all files. It is
now time for Paul to create an independent branch on which to work.
<ol>
<li>Right-click on the <b>brtest</b> project and select <b>Team
&rarr; Branch ...</b>. A dialog is displayed for creating the branch and
marking the start-point with a tag (also called a <i>Version Name</i>).
Enter a branch name like <b>p1test</b>. Leave the check box checked for
<b>Start working in the branch</b>. Notice that a start tag is
automatically filled in for you called <b>Root_p1test</b>. This is the
first tag labeled in the <a href="#scenario">Scenario Diagram</a>. You
may choose a different name so long as it doesn't conflict with an
existing CVS tag. This will mark where the branch was created. It will
be used later by the merge editor to determine what has changed since
branch creation. Click <b>OK</b>.
<p><img src="images/makebranch.jpg"
alt="Dialog for creating a new branch" /></p>
<p>Since you checked the box to start working in the branch, your
workspace should already be configured to work in the branch. You can
verify this in two ways. By right-clicking the project and selecting <b>Properties</b>
and then <b>CVS</b>, you should see the <i>p1test</i> in the tag field.
If you have the CVS label decorations enabled, you'll see the branch
tag in the navigator view (see below).</p>
<p><img src="images/branchlist.jpg"
alt="CVS labels indicating new branch" /></p>
<div class="note"">
<table class="note-table">
<tbody>
<tr>
<td><img alt="[Note]" src="images/tip.gif"></td>
<td>To enable CVS label decorations, go to <b>Window &rarr;
Preferences</b> and navigate to <b>General &rarr; Appearance &rarr;
Label Decorations</b>. Check the 'CVS' box.</td>
</tr>
</tbody>
</table>
</div>
</li>
<li>This step begins the work represented as the blue box labeled
<b>PD1</b> in the <a href="#scenario">Scenario Diagram</a>. Paul will
modify the first file using the <i>p1test</i> branch. Open the editor
for <code>f1.txt</code>. Change line 3 from "This line will be changed
later" to "This line changed in iter1." Save the change.
</li>
<li>Open the editor for <code>f3trivial.txt</code>. Change line 3
from "This line will be changed by Paul only" to "This line changed by
Paul in iter1." Save the change.
</li>
<li>Open the editor for <code>f4conflict.txt</code>. Change line 3
from "This line will be changed by both Paul and Wing" to "This line
changed by Paul in iter1." Save the change.
</li>
<li>Right-click on the <b>brtest</b> project and select <b>Team
&rarr; Synchronize with Repository</b>. In the <b>Outgoing Mode</b> view,
right-click the <b>brtest</b> project folder and select <b>Commit</b>.
Enter a comment such as "First iteration changes made by Paul." Note
that for files that have changed, the revision numbers are four digits.
This is a CVS convention for branched revisions.
<p><img src="images/p1commit.jpg"
alt="Paul's CVS label decorations after commit" /></p>
<p>This commit is represented by the first red circle on the <i>p1test</i>
branch of the Scenario Diagram.</p>
</li>
<li>(<i>Optional <a name="howtotag">tag step</a>, only
required for the merge-again scenario</i>) Paul is finished development for
this iteration. So he will <a name="howtotag">tag</a> this milestone
with <b>P1</b>. This tag will represent the base-point for the
merge-again scenario. Right-click the <b>brtest</b> project and select
<b>Team &rarr; Tag as Version ...</b>. In the dialog that arises, enter
<b>P1</b> for the tag name and click <b>OK</b>. This corresponds to the
<b>P1</b> tag in the <a href="#scenario">Scenario Diagram</a>.
<div class="note">
<table class="note-table">
<tbody>
<tr>
<td><img alt="[Note]" src="images/tip.gif"></td>
<td>To to verify a tag was created, change to the CVS
Repository view and expand <b>Versions &rarr; brtest.</b> The <b>P1</b>
tag should be visible.</td>
</tr>
</tbody>
</table>
</div>
<p>Now it is Wing's turn. Her work is represented in the <a
href="#scenario">Scenario Diagram</a> by the blue box labeled <b>WD1</b>.
</p>
</li>
<li>Wing will make her changes in the main branch. In her
workspace she connects to CVS as "wing" to checkout the <b>brtest</b>
project from CVS.
<p><img src="images/wingcheckout.jpg" alt="" /></p>
She chooses the <b>brtest</b> under <b>HEAD</b>, the moniker CVS uses
to designate the main branch.
<p>Since Wing has the main branch loaded into her workspace, she
doesn't need to perform a branch change. As Wing, begin editing <code>f2.txt</code>.
Change "This line will be changed later" to "This line changed by Wing
in iter1." Save the change.</p>
</li>
<li>Edit <code>f3trivial.txt</code> in Wing's workspace. Change
line 9 from "This line will be changed by Wing only" to "This line
changed by Wing in iter1." Save the change.
</li>
<li>Edit <code>f4conflict.txt</code> in Wing's workspace. Change
line 3 from "This line will be changed by Paul and Wing" to "This line
changed by Wing in iter1." Save the change.
</li>
<li>Commit Wing's changes with a comment like "First iteration
changes by Wing". Note her revisions numbers are all two digits (e.g.
1.2). That's because her new revisions occur on the main branch. This
commit is represented by the first red circle on the main branch in the
<a href="#scenario">Scenario Diagram</a>.
</li>
<li>(<i>Optional tag step, not required anywhere.</i>) Since it is
a good practice to tag a milestone or a recovery point, Wing tags this
point with <b>W1</b> in the same manner as the in the <a
href="#howtotag">previous tag</a>. It's a good idea to tag right
before merging something into your branch so you can recover it more
easily even after a commit.
<div class="note">
<table class="note-table">
<tbody>
<tr>
<td><img alt="[Note]" src="images/tip.gif"></td>
<td>To to verify a tag was created, change to the CVS
Repository view and expand <b>Versions &rarr; brtest.</b> The <b>W1</b>
tag should be visible.</td>
</tr>
</tbody>
</table>
</div>
</li>
</ol>
<h2>The Merge</h2>
Now it is time for Paul to merge his changes into the main branch where
Wing's work resides. This is designated with the <b>M1</b> diamond in
the <a href="#scenario">Scenario Diagram</a>.
<ol start="12">
<li>The first step of the merge is to point the workspace to the
target branch. In our case, the target of the merge is the main branch.
To switch the project contents to that of the main branch, right-click
on the <b>brtest</b> project in the Navigator view and select <b>Replace
with --&gt; Branch or Version ...</b>. You should see a branch selection
similar to the one below. (If you performed the optional tagging steps,
you may see some of those under <i>Versions</i>. You may have to click
<b>Refresh Tags</b> to see them all.)
<p><img src="images/branchswitch2.jpg"
alt="Dialog for selecting new branch or version" /></p>
</li>
<li>The <i>p1test</i> branch is the one Paul was working on. To
switch back to the main branch, select <b>HEAD</b>. This is the CVS
name for the main branch. Then click <b>OK</b>.
<p>The resource view should look like the one below. Notice the
version numbers correspond to what Wing committed. All the version
numbers are two digits. The branch name is gone which implies the <i>HEAD</i>
branch (or main).</p>
<p><img src="images/afterswitch.jpg"
alt="Resource view after switching back to main branch" /></p>
</li>
<li>Right-click on the <b>brtest</b> project and select <b>Team
&rarr; Merge ...</b>. Click the <b>Browse</b> button next to the <b>Branch
or version to be merged</b> field. Choose the <b>p1test</b> branch from the
<b>Choose End Tag</b> dialog box. If you don't see the branch, you may
have to click <b>Refresh tags</b>. Click <b>OK</b>.
<p><img src="images/mergestartpoint2.jpg"
alt="Dialog for choosing a merge start point" /></p>
</li>
<li>The start tag should be filled automatically with <b>Root_p1test</b>.
In this case, the dialog anticipated correctly. For this merge, we have
elected <b>not</b> to check the <b>Merge non-conflicting changes</b>
checkbox. In the merge-again scenario, we will check it and compare the
difference. Click <b>Finish</b>.
<p><img src="images/mergewhat3.jpg"
alt="Dialog for selecting choosing a branch to merge" /></p>
<div class="note">
<table class="note-table">
<tbody>
<tr>
<td><img alt="[Note]" src="images/tip.gif"></td>
<td>Instead of browsing for the end tag, you could have taken
advantage of Content Assist (through Ctrl + Space Bar) as indicated
by the tiny light bulb next to the field.</td>
</tr>
</tbody>
</table>
</div>
</li>
<li>This is where the fun begins. You will be presented with the <i>Synchronize</i>
view with the following merge results:
<p><img src="images/conflict1.jpg" alt="Merge tasks." /></p>
<p><code>f1.txt</code> was not changed by Wing, so it will be
locally updated without a problem. But <code>f3trivial.txt</code> and <code>f4conflict.txt</code>
were each modified by both Paul and Wing and are indicated with the red
double-headed arrows.</p>
</li>
<li>Right-click on the <b>brtest</b> folder and select <b>Merge</b>.
CVS will attempt to work out if there are any changes that are in
conflict between Paul's local version and the repository. In our
example, it updates <code>f1.txt</code> as well as <code>f3trivial.txt</code>
as it was able to resolve the conflicts there. However, <code>f4trivial.txt
</code>presents it with a challenge and Eclipse will alert you that it was not
able to automatically merge the changes.
<center><img src="images/threat1.jpg" alt="" /></center>
<p>As ominous as this appears, it's merely a reminder that we have
to resolve some merge conflicts because they were not auto-mergeable.
We could have avoided the spectacle of this message if we had simply
checked the <b>Merge non-conflicting changes</b> checkbox.</p>
<p>Now lets resolve the conflicts.</p>
</li>
<li>Double-click <code>f4conflict.txt</code> in the <i>Synchronize</i>
view to open the <i>Compare</i> editor of the merge tool. The left side
of the <i>Text Compare</i> panel is the local copy of the main branch
contents. The right side is the <b>brtest</b> branch contents. Since
this is not a trivial merge, the color red is used to delineate the
scope of each merge conflict. Blue would be used to denote trivial
merges.
<p><img src="images/conflict8.jpg"
alt="Resolving conflicts with merge editor" /></p>
<p>We can't resolve this conflict by simply using one side or the
other. For this case, we edit the text in the left side (local file) to
say "This line changed by Paul and Wing in iter1." Right-click in this
same text window and select <b>Save</b>.</p>
</li>
<li>Even after the save, the entry in the conflict editor remains
red. That's because from the Eclipse SCM perspective, there is still a
conflict. It's just a conflict with some extra changes. We have to
explicitly inform the Eclipse SCM that we have indeed resolved the
conflict and that from this point onward, the changes to the local copy
should be interpreted relative to the contents of the left-side.
<center><img src="images/markmerged.jpg" alt="" /></center>
<p>This is done by right-clicking the file in the <i>Synchronize</i>
view and selecting <b>Mark as Merged</b>. Do this now and notice there
are no more conflicts.</p>
<div class="note">
<table class="note-table">
<tbody>
<tr>
<td><img alt="[Note]" src="images/tip.gif"></td>
<td>In Eclipse 3.3, the <b>Mark as Merged</b> action is also
available from the context menu of the compare editor.</td>
</tr>
</tbody>
</table>
</div>
<p>We have now completed merging the changes.</p>
</li>
<li>At this point, the merged copy only exists in our workspace.
We still need to commit it to the CVS repository. Select the <b>brtest</b>
project in the <i>Navigator</i> view and select <b>Team &rarr;
Synchronize with Repository</b>. These changes should not present any
conflicts. Right-click on the <b>brtest</b> folder in the <i>Synchronize</i>
view and select <b>Commit</b>. A suitable comment would be "Merged
p1test branch up to P1 into main."
</li>
<li>Tag the result as <b>WM1</b>. This corresponds to the <b>WM1</b>
tag in the <a href="#scenario">Scenario Diagram</a>.
</li>
<li>Be sure to update Wing's workspace with the results of the
merge.</li>
</ol>
<h2>Check Point</h2>
This completes the branch-and-merge scenario for Iteration 1. The next
section continues with a merge-again example. But let's pause for a
moment to review what we have done.
<p>Several files were used to demonstrate different types of
conflicts that arise during merge activity. In cases where two
developers edited the same file, we saw that CVS was able to
automatically merge trivial changes. Where manual intervention was
required, we saw how to use the merge editor to manually resolve these
conflicts.</p>
<p>After the merge task was complete, we tagged the results to
create a release. Others can then refer to this release using the name
"p12merge." A summary of our actions for a single file is obtained by
right-clicking on the file in the <i>Navigator</i> view and selecting <b>Team
&rarr; Show History</b>. The history for <code>f4conflict.txt</code> is
shown below.</p>
<p><img src="images/f4history2.jpg"
alt="f4conflict.txt revision history"></p>
<p>We can see that the <i>Root_p1test</i> tag is assigned to
revision 1.1, the initial version. We see that Paul made changes that
were committed to a branch while Wing made changes that were committed
to main. Finally, the merge resulted in revision 1.3, which was tagged
for posterity with the label <b>WM1</b>.</p>
<p>For many cases, this may be the only merge scenario you need. It
is certainly sufficient for short-lived branches that introduce a new
feature, test it, and then merge it into the main branch. For longer
running branches where multiple merges are required, the following
merge-again scenario is useful.</p>
<h2>Merge Again</h2>
This is where Paul and Wing each continue to work on their own branch
and synchronize again at a later time. These steps are part of <i>Iteration
2</i> in the <a href="#scenario">Scenario Diagram</a>. The file editing is
very similar to <i>Iteration 1</i>. More emphasis will be placed on the
merging.
<p>The following steps begin in Paul's workspace, which should still
be pointing to the <b>p1test</b> branch. If this is not the case, switch
to the <b>p1test</b> branch through the usual method of right-clicking
the project and selecting <b>Replace with &rarr; Another Branch or
Version</b>.</p>
<ol>
<li>Open <tt>f1.txt</tt>. Change line 5 to read "This line changed
in iter2."
</li>
<li>Open <tt>f3trivial.txt</tt> and change line 5 to read "This
line changed by Paul in iter2."
</li>
<li>Open <tt>f4conflict.txt</tt> and change line 5 to read "This
line changed by Paul in iter2.".
</li>
<li>Save the changes. This completes the work represented by <b>PD2</b>
in the <a href="#scenario">Scenario Diagram</a>. Commit these changes
using a comment such as "Second iteration changes made by Paul."
</li>
<li>Tag this state of the project with <b>P2</b> using <b>Team
&rarr; Tag as Version</b>. This corresponds to the <b>P2</b> tag in the <a
href="#scenario">Scenario Diagram</a>.
<p>Wing will continue her work in her own workspace. It should
already be pointing to the main branch. This work is denoted by <b>WD2</b>
on the scenario diagram.</p>
</li>
<li>In Wing's workspace, open <tt>f2.txt</tt> and edit line 5 to
read "This line changed by Wing in iter2.".
</li>
<li>Open <tt>f3trivial.txt</tt> and change line 11 to read "This
line changed by Wing in iter2."
</li>
<li>Open <tt>f4conflict.txt</tt> and change line 5 to read "This
line changed by Wing in iter2."
</li>
<li>Save the changes. This completes the work represented by <b>WD2</b>
in the <a href="#scenario">Scenario Diagram</a>. Commit these changes
using a comment such as "Second iteration changes made by Wing."
</li>
<li>Tag this state of the project with <b>W2</b>, referring a <a
href="#howtotag">previous tag step</a> if needed.
<p>Paul and Wing have both finished their <i>Iteration 2</i> work.
This time Wing will perform the merge herself from within her own
workspace.</p>
</li>
<li>As Wing, in her workspace, click the <b>brtest</b> project and
select <b>Team &rarr; Merge</b>.
</li>
<li>Click <b>Browse</b> next to the <b>end tag</b> field. Under <b>Branches</b>,
select <b>p1test</b>. If the branch is not visible yet, select <b>Refresh
Tags</b>. (Or you can simply use Content Assist.) Click <b>OK</b>.
<p>Notice that the <b>start tag</b> is populated already. But this
is not the value we want. Upon review of the <a href="#scenario">Scenario
Diagram</a> we see that all we want to merge into main are the changes in
the blue box labeled <b>PD2</b>. But if we specify <b>Root_p1test</b>
in the <b>start tag</b> field, we would also be merging in changes from
the blue box labeled <b>PD1</b>. The <b>PD1</b> changes were already
merged during Iteration 1. Using this default start tag would cause the
same changes to be applied twice. This should be avoided even though it
still works in many cases.</p>
<p>To apply only the changes since the last merge, we want to
specify the <b>P1</b> tag. This encapsulates precisely the <b>PD2</b>
development work.</p>
</li>
<li>Click <b>Browse</b> next to the <b>start tag</b> field and
select <b>P1</b> from the list of tags. Click <b>OK</b>.
</li>
<li>Be sure to check <b>Merge non-conflicting changes</b> so that
the auto-mergeable differences are applied automatically.
<p><img src="images/mergeDialog11.jpg" alt="" /></p>
<p>Click <b>Finish</b>.</p>
<p>You should see the usual <b>Merge Failure</b> dialog indicating
that a non-auto-mergeable conflict was encountered. Click <b>OK</b> so
we can get to work on resolving the conflict.</p>
</li>
<li>The <i>Synchronize</i> view shows that, like before, <code>f4conflict.txt</code>
is the only file with a conflict. Double-click it to view the conflict
in the Text Compare editor. Shown below is the most important
screen-shot of the merge-again scenario.
<p><img src="images/conflict4.jpg" alt="" /></p>
<p>Notice there are two differences, but only one conflict. The
first difference is not marked in red. That's because this line 3 <b>was
not changed since the P1 tag</b>. If we had allowed the start tag of the
merge dialog to remain at <b>Root_p1test</b>, this would have been
interpreted as a change and hence a conflict. If we had not had the
conflict in the second change of line 5, this would have auto-merged
successfully.</p>
<p>Another point to note is that the reason there is even any
difference at all in line 3 is that we are not rebasing in this
scenario. This is why line 3 of the branch is not in sync with line3 of
main, even though it line 3 hasn't been changed since Iteration 1.
Rebasing is addressed in <a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html">Part 2</a> of this
article.</p>
<p>The following steps simply repeat the conflict resolution of
Iteration 1. This is represented by yellow diamond labeled <b>M2</b> in
the scenario diagram. They are recounted here briefly.</p>
</li>
<li>Edit line 5 of the local file to say, "This line changed by
Paul and Wing in iter2."
</li>
<li>Right-click in the local file area and select <b>Save</b>.
</li>
<li>Right-click the <code>f4conflict.txt</code> entry in the <i>Synchronize</i>
view and select <b>Mark as Merged</b>.
</li>
<li>Commit the merge with comment "Merged p1test branch from P1 to
P2."
</li>
<li>Tag the result <b>WM2</b> as indicated in the <a
href="#scenario">Scenario Diagram</a>.</li>
</ol>
<h2>Summary</h2>
In this tutorial we illustrated the implementation steps for a simple
branch and merge scenario. We then extended it with a merge-again
scenario. We saw how tagging milestones and merge results assist with
future merges. We also saw a subtle effect of using these milestone tags
for a base point rather than simply falling back on the original branch
point.
<p>One consequence of the merge tactic chosen for this article is
that the <b>p1test</b> branch was never refreshed with changes on the
main branch. This may be fine in some circumstances. To keep the <b>p1test</b>
branch synchronized with changes in the main, a rebase technique must be
employed. This is the tactic discussed in <a href="http://www.eclipse.org/articles/article.php?file=Article-BranchingWithEclipseAndCVS/article2.html">Part
2</a> of this article.</p>
<h2>An Alternative - Ongoing Merges</h2>
The Eclipse <i>CVS Merge Synchronization</i> view provides support for <i>Ongoing
Merges</i>. This works by pinning the Merge Synchronization view so that it
continues to be present (behind the scenes) and remembers what has
already been merged. So in the merge-again scenario, if we had had the
Merge Synchronization view pinned since the first merge, then we could
have left the start tag with the default <b>Root_p1test</b>. The CVS
Merge Synchronization view would have remembered the earlier merge
between <b>Root_p1test</b> and <b>P1</b> and not tried to re-apply those
changes.
<p>The <i>Ongoing Merge</i> support works well, but has its
limitations. In the scenario for this article, Paul did the first merge
while Wing did the second. Unless the same workspace is involved
throughout the merge scenario, Ongoing Merge support is not feasible.
But in practice, one generally does use the same workspace for merges,
and so Ongoing Merge support is a great help. It provides these
additional features.</p>
<ol>
<li>Multiple Merge Synchronization views can be pinned. This
enables one to coordinate deliveries from multiple branches.
</li>
<li>Merge Synchronization may be scheduled. You can obtain the
following configuration panel by clicking the Merge Synchronization
menu button (the down arrow) and selecting <b>Schedule ...</b>.
<p><img src="images/configMergeSync.jpg" alt="" /></p>
<p>So you become aware of work committed to other branches on a
regular basis.</p>
</li>
</ol>
<p>The Ongoing Merge support should not entirely supplant tagging.
The merge points should still be tagged for milestone purposes and in
case the pinned Merge Synchronization view somehow becomes unavailable.
The Ongoing Merge support is mentioned in the Eclipse Help under <b>Workbench
User's Guide &rarr; Reference &rarr; Team Support with CVS &rarr; CVS
Merge Synchronization</b>.</p>
<h2>References</h2>
Listed below is the standard reference to which one can refer in
addition to the Eclipse documentation.
<ul>
<li><i>Version Management with CVS</i>, Per Cederqvist et al. <a
href="http://ximbiot.com/cvs/manual">
http://ximbiot.com/cvs/manual</a>. This manual is the standard CVS
reference.
</li>
<li><i>CVS Best Practices</i>, Vivek Venugopalan 2002 <a
href="http://www.tldp.org/REF/CVS-BestPractices/html/">html</a>, <a
href="http://www.tldp.org/REF/CVS-BestPractices/CVS-BestPractices.pdf">pdf</a>(75k)
</li>
</ul>
<h2>Useful Plug-ins</h2>
<ul>
<li>Version Trees provides a graphical view of the versions,
branches and tags for a file. <a
href="http://versiontree.sourceforge.net/">http://versiontree.sourceforge.net/</a>
</li>
<li>TortoiseCVS provides a Windows Explorer extension for working
with CVS. <a href="http://www.tortoisecvs.org">http://www.tortoisecvs.org</a>
</li>
</ul>
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