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<div class="sect1" title="Advanced Merging">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="svn.branchmerge.advanced"></a>Advanced Merging</h2>
</div>
</div>
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<p>Here ends the automated magic. Sooner or later, once you
get the hang of branching and merging, you're going to have to
ask Subversion to merge <span class="emphasis"><em>specific</em></span> changes
from one place to another. To do this, you're going to
have to start passing more complicated arguments to <span class="command"><strong>svn
merge</strong></span>. The next section describes the fully expanded
syntax of the command and discusses a number of common
scenarios that require it.</p>
<div class="sect2" title="Cherrypicking">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.cherrypicking"></a>Cherrypicking</h3>
</div>
</div>
</div>
<p>Just as the term <span class="quote">“<span class="quote">changeset</span>”</span> is often used in
version control systems, so is the term
<em class="firstterm">cherrypicking</em>. This word refers to
the act of choosing <span class="emphasis"><em>one</em></span> specific
changeset from a branch and replicating it to another.
Cherrypicking may also refer to the act of duplicating a
particular set of (not necessarily contiguous!) changesets
from one branch to another. This is in contrast to more
typical merging scenarios, where the <span class="quote">“<span class="quote">next</span>”</span>
contiguous range of revisions is duplicated
automatically.</p>
<p>Why would people want to replicate just a single change?
It comes up more often than you'd think. For example, let's
go back in time and imagine that you haven't yet merged your
private feature branch back to the trunk. At the
water cooler, you get word that Sally made an interesting
change to <code class="filename">integer.c</code> on the trunk.
Looking over the history of commits to the trunk, you see that
in revision 355 she fixed a critical bug that directly
impacts the feature you're working on. You might not be ready
to merge all the trunk changes to your branch just yet, but
you certainly need that particular bug fix in order to continue
your work.</p>
<div class="informalexample">
<pre class="screen">
$ svn diff -c 355 ^/calc/trunk
Index: integer.c
===================================================================
--- integer.c (revision 354)
+++ integer.c (revision 355)
@@ -147,7 +147,7 @@
case 6: sprintf(info->operating_system, "HPFS (OS/2 or NT)"); break;
case 7: sprintf(info->operating_system, "Macintosh"); break;
case 8: sprintf(info->operating_system, "Z-System"); break;
- case 9: sprintf(info->operating_system, "CP/MM");
+ case 9: sprintf(info->operating_system, "CP/M"); break;
case 10: sprintf(info->operating_system, "TOPS-20"); break;
case 11: sprintf(info->operating_system, "NTFS (Windows NT)"); break;
case 12: sprintf(info->operating_system, "QDOS"); break;
</pre>
</div>
<p>Just as you used <span class="command"><strong>svn diff</strong></span> in the prior
example to examine revision 355, you can pass the same option
to <span class="command"><strong>svn merge</strong></span>:</p>
<div class="informalexample">
<pre class="screen">
$ svn merge -c 355 ^/calc/trunk
--- Merging r355 into '.':
U integer.c
--- Recording mergeinfo for merge of r355 into '.':
U .
$ svn status
M integer.c
</pre>
</div>
<p>You can now go through the usual testing procedures before
committing this change to your branch. After the commit,
Subversion marks r355 as having been merged to the branch so
that future <span class="quote">“<span class="quote">magic</span>”</span> merges that synchronize your
branch with the trunk know to skip over r355. (Merging the
same change to the same branch almost always results in a
conflict!)</p>
<div class="informalexample">
<pre class="screen">
$ cd my-calc-branch
$ svn propget svn:mergeinfo .
/trunk:341-349,355
# Notice that r355 isn't listed as "eligible" to merge, because
# it's already been merged.
$ svn mergeinfo ^/calc/trunk --show-revs eligible
r350
r351
r352
r353
r354
r356
r357
r358
r359
r360
$ svn merge ^/calc/trunk
--- Merging r350 through r354 into '.':
U .
U integer.c
U Makefile
--- Merging r356 through r360 into '.':
U .
U integer.c
U button.c
--- Recording mergeinfo for merge of r350 through r360 into '.':
U .
</pre>
</div>
<p>This use case of replicating
(or <em class="firstterm">backporting</em>) bug fixes from one
branch to another is perhaps the most popular reason for
cherrypicking changes; it comes up all the time, for example,
when a team is maintaining a <span class="quote">“<span class="quote">release branch</span>”</span> of
software. (We discuss this pattern in
<a class="xref" href="svn.branchmerge.commonpatterns.html#svn.branchmerge.commonpatterns.release" title="Release Branches">the section called “Release Branches”</a>.)</p>
<div class="warning" title="Warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Warning]" src="images/warning.png" />
</td>
<th align="left">Warning</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Did you notice how, in the last example, the merge
invocation merged two distinct ranges?
The <span class="command"><strong>svn merge</strong></span> command applied
two independent patches to your working copy to skip over
changeset 355, which your branch already contained. There's
nothing inherently wrong with this, except that it has the
potential to make conflict resolution trickier. If the
first range of changes creates conflicts,
you <span class="emphasis"><em>must</em></span> resolve them interactively for
the merge process to continue and apply the second range of
changes. If you postpone a conflict from the first wave of
changes, the whole merge command will bail out with an error
message.<sup>[<a id="idp11412560" href="#ftn.idp11412560" class="footnote">32</a>]</sup></p>
</td>
</tr>
</table>
</div>
<p>A word of warning: while <span class="command"><strong>svn diff</strong></span> and
<span class="command"><strong>svn merge</strong></span> are very similar in concept, they
do have different syntax in many cases. Be sure to read about
them in <a class="xref" href="svn.ref.html" title="Chapter 9. Subversion Complete Reference">Chapter 9, <em>Subversion Complete Reference</em></a> for details, or ask
<span class="command"><strong>svn help</strong></span>. For example, <span class="command"><strong>svn
merge</strong></span> requires a working copy path as a target, that is,
a place where it should apply the generated patch. If the
target isn't specified, it assumes you are trying to perform
one of the following common operations:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>You want to merge directory changes into your current
working directory.</p>
</li>
<li class="listitem">
<p>You want to merge the changes in a specific file into
a file by the same name that exists in your current working
directory.</p>
</li>
</ul>
</div>
<p>If you are merging a directory and haven't specified a
target path, <span class="command"><strong>svn merge</strong></span> assumes the first
case and tries to apply the changes into your current
directory. If you are merging a file, and that file (or a
file by the same name) exists in your current working
directory,
<span class="command"><strong>svn merge</strong></span> assumes the second case and tries
to apply the changes to a local file with the same name.</p>
</div>
<div class="sect2" title="Merge Syntax: Full Disclosure">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.advancedsyntax"></a>Merge Syntax: Full Disclosure</h3>
</div>
</div>
</div>
<p>You've now seen some examples of the <span class="command"><strong>svn
merge</strong></span> command, and you're about to see several more.
If you're feeling confused about exactly how merging works,
you're not alone. Many users (especially those new to version
control) are initially perplexed about the proper syntax of
the command and about how and when the feature should be
used. But fear not, this command is actually much simpler
than you think! There's a very easy technique for
understanding exactly how <span class="command"><strong>svn merge</strong></span>
behaves.</p>
<p>The main source of confusion is the
<span class="emphasis"><em>name</em></span> of the command. The term
<span class="quote">“<span class="quote">merge</span>”</span> somehow denotes that branches are
combined together, or that some sort of mysterious
blending of data is going on. That's not the case. A better
name for the command might have been <span class="command"><strong>svn
diff-and-apply</strong></span>, because that's all that happens:
two repository trees are compared, and the differences are
applied to a working copy.</p>
<p>If you're using <span class="command"><strong>svn merge</strong></span> to do basic
copying of changes between branches, it will generally do the
right thing automatically. For example, a command such as the
following:</p>
<div class="informalexample">
<pre class="screen">
$ svn merge ^/calc/branches/some-branch
</pre>
</div>
<p>will attempt to duplicate any changes made
on <code class="filename">some-branch</code> into your current working
directory, which is presumably a working copy that shares some
historical connection to the branch. The command is smart
enough to only duplicate changes that your working copy
doesn't yet have. If you repeat this command once a week, it
will only duplicate the <span class="quote">“<span class="quote">newest</span>”</span> branch changes
that happened since you last merged.</p>
<p>If you choose to use the <span class="command"><strong>svn merge</strong></span>
command in all its full glory by giving it specific revision
ranges to duplicate, the command takes three main
arguments:</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>An initial repository tree (often called the
<em class="firstterm">left side</em> of the comparison)</p>
</li>
<li class="listitem">
<p>A final repository tree (often called the
<em class="firstterm">right side</em> of the
comparison)</p>
</li>
<li class="listitem">
<p>A working copy to accept the differences as local
changes (often called the <em class="firstterm">target</em> of
the merge)</p>
</li>
</ol>
</div>
<p>Once these three arguments are specified, then the two trees
are compared and the differences applied to the
target working copy as local modifications. When the command
is done, the results are no different than if you had
hand-edited the files or run various <span class="command"><strong>svn
add</strong></span> or <span class="command"><strong>svn delete</strong></span> commands
yourself. If you like the results, you can commit them. If
you don't like the results, you can simply <span class="command"><strong>svn
revert</strong></span> all of the changes.</p>
<p>The syntax of <span class="command"><strong>svn merge</strong></span> allows you to
specify the three necessary arguments rather flexibly. Here
are some examples:</p>
<div class="informalexample">
<pre class="screen">
$ svn merge http://svn.example.com/repos/branch1@150 \
http://svn.example.com/repos/branch2@212 \
my-working-copy
$ svn merge -r 100:200 http://svn.example.com/repos/trunk my-working-copy
$ svn merge -r 100:200 http://svn.example.com/repos/trunk
</pre>
</div>
<p>The first syntax lays out all three arguments explicitly,
naming each tree in the form <span class="emphasis"><em>URL@REV</em></span> and
naming the working copy target. The second syntax is used
as a shorthand for situations when you're comparing two
different revisions of the same URL. The last syntax shows
how the working copy argument is optional; if omitted, it
defaults to the current directory.</p>
<p>While the first example shows the <span class="quote">“<span class="quote">full</span>”</span>
syntax of <span class="command"><strong>svn merge</strong></span>, use it
very carefully; it can result in merges which do not record
any <code class="literal">svn:mergeinfo</code> metadata at all. The
next section talks a bit more about this.</p>
</div>
<div class="sect2" title="Merges Without Mergeinfo">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.nomergedata"></a>Merges Without Mergeinfo</h3>
</div>
</div>
</div>
<p>Subversion tries to generate merge metadata whenever it
can, to make future invocations of <span class="command"><strong>svn
merge</strong></span> smarter. There are still situations, however,
where <code class="literal">svn:mergeinfo</code> data is not created or
changed. Remember to be a bit wary of these scenarios:</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">Merging unrelated sources</span>
</dt>
<dd>
<p>If you ask <span class="command"><strong>svn merge</strong></span> to compare
two URLs that aren't related to each other, a patch is
still generated and applied to your working copy, but
no merging metadata is created. There's no common
history between the two sources, and
future <span class="quote">“<span class="quote">smart</span>”</span> merges depend on that common
history.</p>
</dd>
<dt>
<span class="term">Merging from foreign repositories</span>
</dt>
<dd>
<p>While it's possible to run a command such
as <strong class="userinput"><code>svn merge -r 100:200
<em class="replaceable"><code>http://svn.foreignproject.com/repos/trunk</code></em></code></strong>,
the resultant patch also lacks any historical merge
metadata. At the time of this writing, Subversion has no
way of representing different repository URLs within
the <code class="literal">svn:mergeinfo</code> property.</p>
</dd>
<dt>
<span class="term">Using <code class="option">--ignore-ancestry</code></span>
</dt>
<dd>
<p>If this option is passed to <span class="command"><strong>svn
merge</strong></span>, it causes the merging logic to
mindlessly generate differences the same way
that <span class="command"><strong>svn diff</strong></span> does, ignoring any
historical relationships. We discuss this later in this
chapter in
<a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.advanced.ancestry" title="Noticing or Ignoring Ancestry">the section called “Noticing or Ignoring Ancestry”</a>.</p>
</dd>
<dt>
<span class="term">Applying reverse merges from a target's natural history</span>
</dt>
<dd>
<p>Earlier in this chapter
(<a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchmerge.basicmerging.undo" title="Undoing Changes">the section called “Undoing Changes”</a>) we
discussed how to use <span class="command"><strong>svn merge</strong></span> to
apply a <span class="quote">“<span class="quote">reverse patch</span>”</span> as a way of rolling
back changes. If this technique is used to undo a
change to an object's personal history (e.g., commit r5
to the trunk, then immediately roll back r5
using <strong class="userinput"><code>svn merge . -c -5</code></strong>), this
sort of merge doesn't affect the recorded
mergeinfo.<sup>[<a id="idp11467760" href="#ftn.idp11467760" class="footnote">33</a>]</sup></p>
</dd>
</dl>
</div>
<div class="sidebar" title="Natural History and Implicit Mergeinfo">
<a id="svn.branchmerge.nomergedata.impicit.mergeinfo"></a>
<div class="titlepage">
<div>
<div>
<p class="title">
<strong>Natural History and Implicit Mergeinfo</strong>
</p>
</div>
</div>
</div>
<p>As we mentioned earlier when discussing
<a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchmerge.basicmerging.mergeinfo.inheritance" title="Mergeinfo Inheritance">Mergeinfo Inheritance</a>,
a path that has the
<code class="literal">svn:mergeinfo</code> property set on it is said to
have <span class="quote">“<span class="quote">explicit</span>”</span> mergeinfo. Yes, this implies a
path can have <span class="quote">“<span class="quote">implicit</span>”</span> mergeinfo, too! Implicit
mergeinfo, or <em class="firstterm">natural history</em>, is
simply a path's own history (see
<a class="xref" href="svn.tour.history.html" title="Examining History">the section called “Examining History”</a>) interpreted as mergeinfo.
While implicit mergeinfo is largely
an implementation detail, it can be a useful abstraction for
understanding merge tracking behavior.</p>
<p>Let's say you created <code class="filename">^/trunk</code> in
revision 100 and then later, in revision 201,
created <code class="filename">^/branches/feature-branch</code> as
a copy of <code class="filename">^/trunk@200</code>. The natural
history of <code class="filename">^/branches/feature-branch</code>
contains all the repository paths and revision ranges
through which the history of the new branch has ever
passed:</p>
<div class="informalexample">
<div class="literallayout">
<p><br />
/trunk:100-200<br />
/branches/feature-branch:201<br />
</p>
</div>
</div>
<p>With each new revision added to the repository, the
natural history—and thus, implicit mergeinfo—of
the branch continues to expand to include those revisions
until the day the branch is deleted. Here's what the
implicit mergeinfo of our branch would look like when
the <code class="literal">HEAD</code> revision of the repository had
grown to 234:</p>
<div class="informalexample">
<div class="literallayout">
<p><br />
/trunk:100-200<br />
/branches/feature-branch:201-234<br />
</p>
</div>
</div>
<p>Implicit mergeinfo does not actually show up in the
<code class="literal">svn:mergeinfo</code> property, but Subversion
acts as if it does. This is why if you check out
<code class="filename">^/branches/feature-branch</code> and then
run <strong class="userinput"><code>svn merge ^/trunk -c 58</code></strong> in the
resulting working copy, nothing happens. Subversion knows
that the changes committed to <code class="filename">^/trunk</code>
in revision 58 are already present in the target's natural
history, so there's no need to try to merge them again.
After all, avoiding repeated merges of
changes <span class="emphasis"><em>is</em></span> the primary goal of
Subversion's merge tracking feature!</p>
</div>
</div>
<div class="sect2" title="More on Merge Conflicts">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.mergeconflicts"></a>More on Merge Conflicts</h3>
</div>
</div>
</div>
<p>Just like the <span class="command"><strong>svn update</strong></span> command,
<span class="command"><strong>svn merge</strong></span> applies changes to your working
copy. And therefore it's also capable of creating
conflicts. The conflicts produced by <span class="command"><strong>svn
merge</strong></span>, however, are sometimes different, and this
section explains those differences.</p>
<p>To begin with, assume that your working copy has no
local edits. When you <span class="command"><strong>svn update</strong></span> to a
particular revision, the changes sent by the server
always apply <span class="quote">“<span class="quote">cleanly</span>”</span> to your working copy.
The server produces the delta by comparing two trees: a
virtual snapshot of your working copy, and the revision tree
you're interested in. Because the left hand side of the
comparison is exactly equal to what you already have, the
delta is guaranteed to correctly convert your working copy
into the right hand tree.</p>
<p>But <span class="command"><strong>svn merge</strong></span> has no such guarantees
and can be much more chaotic: the advanced user can ask the
server to compare <span class="emphasis"><em>any</em></span> two trees at all,
even ones that are unrelated to the working copy! This means
there's large potential for human error. Users will sometimes
compare the wrong two trees, creating a delta that doesn't
apply cleanly. The <span class="command"><strong>svn merge</strong></span> subcommand does
its best to apply as much of the delta as possible, but some
parts may be impossible. A common sign that you merged the wrong
delta is unexpected tree conflicts:</p>
<div class="informalexample">
<pre class="screen">
$ svn merge -r 1288:1351 http://svn.example.com/myrepos/branch
--- Merging r1289 through r1351 into '.':
C bar.c
C foo.c
C docs
--- Recording mergeinfo for merge of r1289 through r1351 into '.':
U .
Summary of conflicts:
Tree conflicts: 3
$ svn st
! C bar.c
> local missing, incoming edit upon merge
! C foo.c
> local missing, incoming edit upon merge
! C docs
> local delete, incoming edit upon merge
</pre>
</div>
<p>In the previous example, it might be the case that
<code class="filename">bar.c</code>, <code class="filename">foo.c</code>, and
<code class="filename">docs</code> all exist in both snapshots of the
branch being compared. The resultant delta wants to change
the contents of the corresponding paths in your working copy,
but those paths don't exist in the working copy. Whatever the
case, the preponderance of tree conflicts most likely means that
the user compared the wrong two trees; it's a classic
sign of user error. When this happens, it's easy to
recursively revert all the changes created by the merge
(<strong class="userinput"><code>svn revert . --recursive</code></strong>), delete any
unversioned files or directories left behind after the
revert, and rerun <span class="command"><strong>svn merge</strong></span> with the
correct arguments.</p>
<p>Also keep in mind that a merge into a working copy with no
local edits can still produce text conflicts.</p>
<div class="informalexample">
<pre class="screen">
$ svn merge -c 1701 http://svn.example.com/myrepos/branchX --accept postpone
--- Merging r1701 into '.':
C glub.c
C sputter.c
--- Recording mergeinfo for merge of r1701 into '.':
U .
Summary of conflicts:
Text conflicts: 2
C:\SVN\src-branch-1.7.x>svn st
M .
? glub.c.merge-left.r1700
? glub.c.merge-right.r1701
C glub.c
? glub.c.working
? sputter.c.merge-left.r1700
? sputter.c.merge-right.r1701
C sputter.c
? sputter.c.working
Summary of conflicts:
Text conflicts: 2
</pre>
</div>
<p>How can a conflict possibly happen? Again, because the user
can request <span class="command"><strong>svn merge</strong></span> to define and apply any
old delta to the working copy, that delta may contain textual
changes that don't cleanly apply to a working file, even if
the file has no local modifications.</p>
<p>Another small difference between <span class="command"><strong>svn
update</strong></span> and <span class="command"><strong>svn merge</strong></span> is the names
of the full-text files created when a conflict happens. In
<a class="xref" href="svn.tour.cycle.html#svn.tour.cycle.resolve" title="Resolve Any Conflicts">the section called “Resolve Any Conflicts”</a>, we saw that an
update produces files named
<code class="filename">filename.mine</code>,
<code class="filename">filename.rOLDREV</code>, and
<code class="filename">filename.rNEWREV</code>. When <span class="command"><strong>svn
merge</strong></span> produces a conflict, though, it creates three
files named <code class="filename">filename.working</code>,
<code class="filename">filename.merge-left.rOLDREV</code>, and
<code class="filename">filename.merge-right.rNEWREV</code>. In this case,
the terms <span class="quote">“<span class="quote">merge-left</span>”</span> and <span class="quote">“<span class="quote">merge-right</span>”</span>
are describing which side of the double-tree comparison the file
came from, <span class="quote">“<span class="quote">rOLDREV</span>”</span> describes the revision of the
left side, and <span class="quote">“<span class="quote">rNEWREV</span>”</span> the revision of the right
side. In any case, these differing names help you distinguish
between conflicts that happened as a result of an update and
ones that happened as a result of a merge.</p>
</div>
<div class="sect2" title="Blocking Changes">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.blockchanges"></a>Blocking Changes</h3>
</div>
</div>
</div>
<p>Sometimes there's a particular changeset that you don't
want automatically merged. For example, perhaps your
team's policy is to do new development work on
<code class="filename">/trunk</code>, but is more conservative about
backporting changes to a stable branch you use for releasing
to the public. On one extreme, you can manually cherrypick
single changesets from the trunk to the branch—just the
changes that are stable enough to pass muster. Maybe things
aren't quite that strict, though; perhaps most of the time
you just let <span class="command"><strong>svn merge</strong></span>
automatically merge most changes from trunk to branch. In
this case, you want a way to mask a few specific changes
out, that is, prevent them from ever being automatically
merged.</p>
<p>Through Subversion 1.7, the only way to block a changeset
is to make the system believe that the change has
<span class="emphasis"><em>already</em></span> been merged. To do this, invoke
the merge subcommand with the <code class="option">--record-only</code>
option:</p>
<div class="informalexample">
<pre class="screen">
$ cd my-calc-branch
$ svn propget svn:mergeinfo .
/trunk:1680-3305
# Let's make the metadata list r3328 as already merged.
$ svn merge -c 3328 --record-only ^/calc/trunk
--- Recording mergeinfo for merge of r3328 into '.':
U .
$ svn status
M .
$ svn propget svn:mergeinfo .
/trunk:1680-3305,3328
$ svn commit -m "Block r3328 from being merged to the branch."
…
</pre>
</div>
<p>Beginning with Subversion 1.7, <code class="option">--record-only</code>
merges are transitive. This means that, in addition to recording
mergeinfo describing the blocked revision(s), any
<code class="literal">svn:mergeinfo</code> property differences in the
merge source are also applied. For example, let's say we want to
block the 'frazzle' feature from ever being merged from
<code class="filename">^/trunk</code> to our
<code class="filename">^/branches/proj-X</code> branch. We know that all
the frazzle work was done on its own branch, which was
reintegrated to <code class="filename">trunk</code> in revision 1055:</p>
<div class="informalexample">
<pre class="screen">
$ svn log -v ^/trunk -r 1055
------------------------------------------------------------------------
r1055 | francesca | 2011-09-22 07:40:06 -0400 (Thu, 22 Sep 2011) | 3 lines
Changed paths:
M /trunk
M /trunk/src/frazzle.c
Reintegrate the frazzle-feature-branch to trunk.
</pre>
</div>
<p>Because revision 1055 was a reintegrate merge we know
that mergeinfo was recorded describing the merge:</p>
<div class="informalexample">
<pre class="screen">
$ svn diff ^/trunk -c 1055 --depth empty
Index: .
===================================================================
--- . (revision 1054)
+++ . (revision 1055)
Property changes on: .
___________________________________________________________________
Modified: svn:mergeinfo
Merged /branches/frazzle-feature-branch:r997-1003
</pre>
</div>
<p>Now simply blocking merges of revision 1055 from
<code class="filename">^/trunk</code> isn't foolproof since someone could
merge r996:1003 directly from
<code class="filename">^/branches/frazzle-feature-branch</code>.
Fortunately the transitive nature
of <code class="option">--record-only</code> merges in Subversion 1.7
prevents this; the <code class="option">--record-only</code> merge
applies the <code class="literal">svn:mergeinfo</code> diff from
revision 1055, thus blocking merges directly from the frazzle
branch <span class="emphasis"><em>and</em></span> as it has always done prior to
Subversion 1.7, it blocks merges of revision 1055 directly
from <code class="filename">^/trunk</code>:</p>
<div class="informalexample">
<pre class="screen">
$ cd branches/proj-X
$ svn merge ^/trunk . -c 1055 --record-only
--- Merging r1055 into '.':
G .
--- Recording mergeinfo for merge of r1055 into '.':
G .
$ svn diff --depth empty .
Index: .
===================================================================
--- . (revision 1070)
+++ . (working copy)
Property changes on: .
___________________________________________________________________
Modified: svn:mergeinfo
Merged /trunk:r1055
Merged /branches/frazzle-feature-branch:r997-1003
</pre>
</div>
<p>Blocking changes with <code class="option">--record-only</code>
works, but it's also a little bit
dangerous. The main problem is that we're not clearly
differentiating between the ideas of <span class="quote">“<span class="quote">I already have
this change</span>”</span> and <span class="quote">“<span class="quote">I don't have this change, but
don't currently want it.</span>”</span> We're effectively lying to
the system, making it think that the change was previously
merged. This puts the responsibility on you—the
user—to remember that the change wasn't actually merged,
it just wasn't wanted. There's no way to ask Subversion for a
list of <span class="quote">“<span class="quote">blocked changelists.</span>”</span> If you want to
track them (so that you can unblock them someday) you'll need
to record them in a text file somewhere, or perhaps in an
invented property.</p>
</div>
<div class="sect2" title="Keeping a Reintegrated Branch Alive">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.reintegratetwice"></a>Keeping a Reintegrated Branch Alive</h3>
</div>
</div>
</div>
<p>There is an alternative to destroying and re-creating a
branch after reintegration. To understand why it works you need
to understand why the branch is initially unfit for further use
after it has been reintegrated.</p>
<p>Let's assume you created your branch in revision
<span class="emphasis"><em>A</em></span>. While working on your branch, you created
one or more revisions which made changes to the branch.
Before reintegrating your branch back to trunk, you made a final
merge from trunk to your branch, and committed the result of
this merge as revision <span class="emphasis"><em>B</em></span>.</p>
<p>When reintegrating your branch into the trunk, you create
a new revision <span class="emphasis"><em>X</em></span> which changes the trunk.
The changes made to trunk in this revision <span class="emphasis"><em>X</em></span>
are semantically equivalent to the changes you made to your branch
between revisions <span class="emphasis"><em>A</em></span> and <span class="emphasis"><em>B</em></span>.</p>
<p>If you now try to merge outstanding changes from trunk to your
branch, Subversion will consider changes made in revision
<span class="emphasis"><em>X</em></span> as eligible for merging into the
branch. However, since your branch already contains all the
changes made in revision <span class="emphasis"><em>X</em></span>, merging these
changes can result in spurious conflicts! These conflicts are
often tree conflicts, especially if renames were made on the
branch or the trunk while the branch was in development.</p>
<p>So what can be done about this? We need to make sure that
Subversion does not try to merge revision <span class="emphasis"><em>X</em></span>
into the branch. This is done using the
<code class="option">--record-only</code> merge option, which was introduced
in <a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.advanced.blockchanges" title="Blocking Changes">the section called “Blocking Changes”</a>.</p>
<p>To carry out the record-only merge, get a working copy of
the branch which was just reintegrated in revision
<span class="emphasis"><em>X</em></span>, and merge just revision <span class="emphasis"><em>X</em></span>
from trunk into your branch, making sure to use the
<code class="option">--record-only</code> option.</p>
<p>This merge uses the cherry-picking merge syntax, which was
introduced in <a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.cherrypicking" title="Cherrypicking">the section called “Cherrypicking”</a>.
Continuing with the running example from
<a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchemerge.basicmerging.reintegrate" title="Reintegrating a Branch">the section called “Reintegrating a Branch”</a>,
where revision <span class="emphasis"><em>X</em></span> was revision 391:</p>
<div class="informalexample">
<pre class="screen">
$ cd my-calc-branch
$ svn update
Updating '.':
Updated to revision 393.
$ svn merge --record-only -c 391 ^/calc/trunk
--- Recording mergeinfo for merge of r391 into '.':
U .
$ svn commit -m "Block revision 391 from being merged into my-calc-branch."
Sending .
Committed revision 394.
</pre>
</div>
<p>Now your branch is ready to soak up changes from the trunk
again. After another sync of your branch to the trunk, you can
even reintegrate the branch a second time.
If necessary, you can do another record-only merge to keep the
branch alive. Rinse and repeat.</p>
<p>It should now also be apparent why deleting the branch and
re-creating it has the same effect as doing the above record-only
merge. Because revision <span class="emphasis"><em>X</em></span> is part of the natural
history (see the sidebar
<a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.nomergedata.impicit.mergeinfo" title="Natural History and Implicit Mergeinfo">Natural History and Implicit Mergeinfo</a>)
of the newly created branch, Subversion will never attempt to
merge revision <span class="emphasis"><em>X</em></span> into the branch, avoiding
spurious conflicts.</p>
</div>
<div class="sect2" title="Merge-Sensitive Logs and Annotations">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.logblame"></a>Merge-Sensitive Logs and Annotations</h3>
</div>
</div>
</div>
<p>One of the main features of any version control system is
to keep track of who changed what, and when they did it.
The <span class="command"><strong>svn log</strong></span> and <span class="command"><strong>svn
blame</strong></span> subcommands are just the tools for this: when
invoked on individual files, they show not only the history of
changesets that affected the file, but also exactly which user
wrote which line of code, and when she did it.</p>
<p>When changes start getting replicated between branches,
however, things start to get complicated. For example, if you
were to ask <span class="command"><strong>svn log</strong></span> about the history of
your feature branch, it would show exactly every revision that ever
affected the branch:</p>
<div class="informalexample">
<pre class="screen">
$ cd my-calc-branch
$ svn log -q
------------------------------------------------------------------------
r390 | user | 2002-11-22 11:01:57 -0600 (Fri, 22 Nov 2002)
------------------------------------------------------------------------
r388 | user | 2002-11-21 05:20:00 -0600 (Thu, 21 Nov 2002)
------------------------------------------------------------------------
r381 | user | 2002-11-20 15:07:06 -0600 (Wed, 20 Nov 2002)
------------------------------------------------------------------------
r359 | user | 2002-11-19 19:19:20 -0600 (Tue, 19 Nov 2002)
------------------------------------------------------------------------
r357 | user | 2002-11-15 14:29:52 -0600 (Fri, 15 Nov 2002)
------------------------------------------------------------------------
r343 | user | 2002-11-07 13:50:10 -0600 (Thu, 07 Nov 2002)
------------------------------------------------------------------------
r341 | user | 2002-11-03 07:17:16 -0600 (Sun, 03 Nov 2002)
------------------------------------------------------------------------
r303 | sally | 2002-10-29 21:14:35 -0600 (Tue, 29 Oct 2002)
------------------------------------------------------------------------
r98 | sally | 2002-02-22 15:35:29 -0600 (Fri, 22 Feb 2002)
------------------------------------------------------------------------
</pre>
</div>
<p>But is this really an accurate picture of all the changes
that happened on the branch? What's left out here is
the fact that revisions 390, 381, and 357 were actually the
results of merging changes from the trunk. If you look at one
of these logs in detail, the multiple trunk changesets that
comprised the branch change are nowhere to be seen:</p>
<div class="informalexample">
<pre class="screen">
$ svn log -v -r 390
------------------------------------------------------------------------
r390 | user | 2002-11-22 11:01:57 -0600 (Fri, 22 Nov 2002) | 1 line
Changed paths:
M /branches/my-calc-branch/button.c
M /branches/my-calc-branch/README
Final merge of trunk changes to my-calc-branch.
</pre>
</div>
<p>We happen to know that this merge to the branch was
nothing but a merge of trunk changes. How can we see those
trunk changes as well? The answer is to use the
<code class="option">--use-merge-history</code> (<code class="option">-g</code>)
option. This option expands those <span class="quote">“<span class="quote">child</span>”</span>
changes that were part of the merge.</p>
<div class="informalexample">
<pre class="screen">
$ svn log -v -r 390 -g
------------------------------------------------------------------------
r390 | user | 2002-11-22 11:01:57 -0600 (Fri, 22 Nov 2002) | 1 line
Changed paths:
M /branches/my-calc-branch/button.c
M /branches/my-calc-branch/README
Final merge of trunk changes to my-calc-branch.
------------------------------------------------------------------------
r383 | sally | 2002-11-21 03:19:00 -0600 (Thu, 21 Nov 2002) | 2 lines
Changed paths:
M /branches/my-calc-branch/button.c
Merged via: r390
Fix inverse graphic error on button.
------------------------------------------------------------------------
r382 | sally | 2002-11-20 16:57:06 -0600 (Wed, 20 Nov 2002) | 2 lines
Changed paths:
M /branches/my-calc-branch/README
Merged via: r390
Document my last fix in README.
</pre>
</div>
<p>By making the log operation use merge history, we see not
just the revision we queried (r390), but also the two revisions
that came along on the ride with it—a couple of changes
made by Sally to the trunk. This is a much more complete
picture of history!</p>
<p>The <span class="command"><strong>svn blame</strong></span> command also takes the
<code class="option">--use-merge-history</code> (<code class="option">-g</code>)
option. If this option is neglected, somebody looking at
a line-by-line annotation of <code class="filename">button.c</code> may
get the mistaken impression that you were responsible for the
lines that fixed a certain error:</p>
<div class="informalexample">
<pre class="screen">
$ svn blame button.c
…
390 user retval = inverse_func(button, path);
390 user return retval;
390 user }
…
</pre>
</div>
<p>And while it's true that you did actually commit those
three lines in revision 390, two of them were actually written
by Sally back in revision 383:</p>
<div class="informalexample">
<pre class="screen">
$ svn blame button.c -g
…
G 383 sally retval = inverse_func(button, path);
G 383 sally return retval;
390 user }
…
</pre>
</div>
<p>Now we know who to <span class="emphasis"><em>really</em></span> blame for
those two lines of code!</p>
</div>
<div class="sect2" title="Noticing or Ignoring Ancestry">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.ancestry"></a>Noticing or Ignoring Ancestry</h3>
</div>
</div>
</div>
<p>
<a id="idp11584416" class="indexterm"></a>
When conversing with a Subversion developer, you might
very likely hear reference to the term
<em class="firstterm">ancestry</em>. This word is used to
describe the relationship between two objects in a
repository: if they're related to each other, one
object is said to be an ancestor of the other.</p>
<p>For example, suppose you commit revision 100, which
includes a change to a file <code class="filename">foo.c</code>.
Then <code class="filename">foo.c@99</code> is an
<span class="quote">“<span class="quote">ancestor</span>”</span> of <code class="filename">foo.c@100</code>.
On the other hand, suppose you commit the deletion of
<code class="filename">foo.c</code> in revision 101, and then add a
new file by the same name in revision 102. In this case,
<code class="filename">foo.c@99</code> and
<code class="filename">foo.c@102</code> may appear to be related
(they have the same path), but in fact are completely
different objects in the repository. They share no history
or <span class="quote">“<span class="quote">ancestry.</span>”</span></p>
<p>The reason for bringing this up is to point out an
important difference between <span class="command"><strong>svn diff</strong></span> and
<span class="command"><strong>svn merge</strong></span>. The former command ignores
ancestry, while the latter command is quite sensitive to it.
For example, if you asked <span class="command"><strong>svn diff</strong></span> to
compare revisions 99 and 102 of <code class="filename">foo.c</code>,
you would see line-based diffs; the <span class="command"><strong>diff</strong></span>
command is blindly comparing two paths. But if you asked
<span class="command"><strong>svn merge</strong></span> to compare the same two objects,
it would notice that they're unrelated and first attempt to
delete the old file, then add the new file; the output would
indicate a deletion followed by an add:</p>
<div class="informalexample">
<pre class="screen">
D foo.c
A foo.c
</pre>
</div>
<p>Most merges involve comparing trees that are ancestrally
related to one another; therefore, <span class="command"><strong>svn
merge</strong></span> defaults to this behavior. Occasionally,
however, you may want the <span class="command"><strong>merge</strong></span> command to
compare two unrelated trees. For example, you may have
imported two source-code trees representing different vendor
releases of a software project (see
<a class="xref" href="svn.advanced.vendorbr.html" title="Vendor Branches">the section called “Vendor Branches”</a>). If you ask
<span class="command"><strong>svn merge</strong></span> to compare the two trees, you'd
see the entire first tree being deleted, followed by an add
of the entire second tree! In these situations, you'll want
<span class="command"><strong>svn merge</strong></span> to do a path-based comparison
only, ignoring any relations between files and directories.
Add the <code class="option">--ignore-ancestry</code> option to your
<span class="command"><strong>merge</strong></span> command, and it will behave just
like <span class="command"><strong>svn diff</strong></span>. (And conversely, the
<code class="option">--notice-ancestry</code> option will cause
<span class="command"><strong>svn diff</strong></span> to behave like the
<span class="command"><strong>svn merge</strong></span> command.)</p>
<div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td align="left" valign="top">
<p>The <code class="option">--ignore-ancestry</code> option also disables
<a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchmerge.basicmerging.mergetracking" title="Merge Tracking">Merge Tracking</a>.
This means that <code class="literal">svn:mergeinfo</code> is not considered
when <span class="command"><strong>svn merge</strong></span> is determining what revisions
to merge, nor is <code class="literal">svn:mergeinfo</code> recorded to
describe the merge.</p>
</td>
</tr>
</table>
</div>
</div>
<div class="sect2" title="Merges and Moves">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.moves"></a>Merges and Moves</h3>
</div>
</div>
</div>
<p>A common desire is to refactor source code, especially
in Java-based software projects. Files and directories are
shuffled around and renamed, often causing great disruption
to everyone working on the project. Sounds like a perfect
case to use a branch, doesn't it? Just create a branch,
shuffle things around, and then merge the branch back to the
trunk, right?</p>
<p>Alas, this scenario doesn't work so well right now and
is considered one of Subversion's current weak spots. The
problem is that Subversion's <span class="command"><strong>svn update</strong></span>
command isn't as robust as it should be, particularly when
dealing with copy and move operations.</p>
<p>When you use <span class="command"><strong>svn copy</strong></span> to duplicate a
file, the repository remembers where the new file came from,
but it fails to transmit that information to the client which
is running <span class="command"><strong>svn update</strong></span> or <span class="command"><strong>svn
merge</strong></span>. Instead of telling the client, <span class="quote">“<span class="quote">Copy
that file you already have to this new location,</span>”</span> it
sends down an entirely new file. This can lead to
problems, especially because the same thing happens with
renamed files. A lesser-known fact about Subversion is that
it lacks <span class="quote">“<span class="quote">true renames</span>”</span>—the <span class="command"><strong>svn
move</strong></span> command is nothing more than an aggregation
of <span class="command"><strong>svn copy</strong></span> and <span class="command"><strong>svn
delete</strong></span>.</p>
<p>For example, suppose that while working on your private
branch, you rename <code class="filename">integer.c</code>
to <code class="filename">whole.c</code>. Effectively you've created
a new file in your branch that is a copy of the original
file, and deleted the original file. Meanwhile, back
on <code class="filename">trunk</code>, Sally has committed some
improvements to <code class="filename">integer.c</code>. Now you
decide to merge your branch to the trunk:</p>
<div class="informalexample">
<pre class="screen">
$ cd calc/trunk
$ svn merge --reintegrate ^/calc/branches/my-calc-branch
--- Merging differences between repository URLs into '.':
D integer.c
A whole.c
U .
--- Recording mergeinfo for merge between repository URLs into '.':
U .
</pre>
</div>
<p>This doesn't look so bad at first glance, but it's also
probably not what you or Sally expected. The merge operation
has deleted the latest version of
the <code class="filename">integer.c</code> file (the one containing
Sally's latest changes), and blindly added your
new <code class="filename">whole.c</code> file—which is a
duplicate of the <span class="emphasis"><em>older</em></span> version
of <code class="filename">integer.c</code>. The net effect is that
merging your <span class="quote">“<span class="quote">rename</span>”</span> to the trunk has removed
Sally's recent changes from the latest revision!</p>
<p>This isn't true data loss. Sally's changes are still in
the repository's history, but it may not be immediately
obvious that this has happened. The moral of this story is
that until Subversion improves, be very careful about
merging copies and renames from one branch to
another.</p>
</div>
<div class="sect2" title="Blocking Merge-Unaware Clients">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.pre1.5clients"></a>Blocking Merge-Unaware Clients</h3>
</div>
</div>
</div>
<p>If you've just upgraded your server to Subversion 1.5 or
later, there's a risk that pre-1.5 Subversion
clients can cause problems with
<a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchmerge.basicmerging.mergetracking" title="Merge Tracking">Merge Tracking</a>.
This is because pre-1.5 clients don't support this feature;
when one of these older clients performs <span class="command"><strong>svn
merge</strong></span>, it doesn't modify the value of
the <code class="literal">svn:mergeinfo</code> property at all. So the
subsequent commit, despite being the result of a merge,
doesn't tell the repository about the duplicated
changes—that information is lost. Later on,
when <span class="quote">“<span class="quote">merge-aware</span>”</span> clients attempt automatic
merging, they're likely to run into all sorts of conflicts
resulting from repeated merges.</p>
<p>If you and your team are relying on the merge-tracking
features of Subversion, you may want to configure your
repository to prevent older clients from committing changes.
The easy way to do this is by inspecting
the <span class="quote">“<span class="quote">capabilities</span>”</span> parameter in
the <code class="literal">start-commit</code> hook script. If the
client reports itself as having <code class="literal">mergeinfo</code>
capabilities, the hook script can allow the commit to start.
If the client doesn't report that capability, have the hook
deny the commit.
<a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.advanced.hook-ex1" title="Example 4.1. Merge-tracking gatekeeper start-commit hook script">Example 4.1, “Merge-tracking gatekeeper start-commit hook script”</a> gives an
example of such a hook script:</p>
<div class="example">
<a id="svn.branchmerge.advanced.hook-ex1"></a>
<p class="title">
<strong>Example 4.1. Merge-tracking gatekeeper start-commit hook script</strong>
</p>
<div class="example-contents">
<pre class="programlisting">
#!/usr/bin/env python
import sys
# The start-commit hook is invoked before a Subversion txn is created
# in the process of doing a commit. Subversion runs this hook
# by invoking a program (script, executable, binary, etc.) named
# 'start-commit' (for which this file is a template)
# with the following ordered arguments:
#
# [1] REPOS-PATH (the path to this repository)
# [2] USER (the authenticated user attempting to commit)
# [3] CAPABILITIES (a colon-separated list of capabilities reported
# by the client; see note below)
capabilities = sys.argv[3].split(':')
if "mergeinfo" not in capabilities:
sys.stderr.write("Commits from merge-tracking-unaware clients are "
"not permitted. Please upgrade to Subversion 1.5 "
"or newer.\n")
sys.exit(1)
sys.exit(0)
</pre>
</div>
</div>
<br class="example-break" />
<p>For more information about hook scripts, see
<a class="xref" href="svn.reposadmin.create.html#svn.reposadmin.create.hooks" title="Implementing Repository Hooks">the section called “Implementing Repository Hooks”</a>.</p>
</div>
<div class="sect2" title="The Final Word on Merge Tracking">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.advanced.finalword"></a>The Final Word on Merge Tracking</h3>
</div>
</div>
</div>
<p>The bottom line is that Subversion's merge-tracking
feature has an extremely complex internal implementation, and
the <code class="literal">svn:mergeinfo</code> property is the only
window the user has into the machinery.</p>
<p>Sometimes mergeinfo will appear on paths that you didn't
expect to be touched by an operation. Sometimes mergeinfo
won't be generated at all, when you expect it to.
Furthermore, the management of mergeinfo metadata has a whole
set of taxonomies and behaviors around it, such
as <span class="quote">“<span class="quote">explicit</span>”</span> versus <span class="quote">“<span class="quote">implicit</span>”</span>
mergeinfo, <span class="quote">“<span class="quote">operative</span>”</span>
versus <span class="quote">“<span class="quote">inoperative</span>”</span> revisions, specific
mechanisms of mergeinfo <span class="quote">“<span class="quote">elision,</span>”</span> and
even <span class="quote">“<span class="quote">inheritance</span>”</span> from parent to child
directories.</p>
<p>We've chosen to only briefly cover, if at all, these detailed
topics for a couple of reasons. First, the level of detail is
absolutely overwhelming for a typical user. Second, and more
importantly, the typical user <span class="emphasis"><em>shouldn't</em></span> have
to understand these concepts; they should typically remain in the
background as pesky implementation details. All that said, if you
enjoy this sort of thing, you can get a fantastic overview in a
paper posted at CollabNet's website: <a class="ulink" href="http://www.collab.net/community/subversion/articles/merge-info.html" target="_top">http://www.collab.net/community/subversion/articles/merge-info.html</a>.</p>
<p>For now, if you want to steer clear of the complexities of
merge tracking, we recommend that you follow these simple best
practices:</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>For short-term feature branches, follow the simple
procedure described throughout
<a class="xref" href="svn.branchmerge.basicmerging.html" title="Basic Merging">the section called “Basic Merging”</a>.</p>
</li>
<li class="listitem">
<p>Avoid subtree merges and subtree mergeinfo, perform
merges only on the root of your branches, not on
subdirectories or files (see <a class="xref" href="svn.branchmerge.basicmerging.html#svn.branchemerge.basicmerging.stayinsync.subtree" title="Subtree Merges and Subtree Mergeinfo">Subtree Merges and Subtree Mergeinfo</a>)
.</p>
</li>
<li class="listitem">
<p>Don't ever edit the <code class="literal">svn:mergeinfo</code>
property directly; use <span class="command"><strong>svn
merge</strong></span> with the <code class="option">--record-only</code> option
to effect a desired change to the metadata (as demonstrated in
<a class="xref" href="svn.branchmerge.advanced.html#svn.branchmerge.advanced.blockchanges" title="Blocking Changes">the section called “Blocking Changes”</a>).</p>
</li>
<li class="listitem">
<p>Your merge target should be a working copy which
represents the root of a <span class="emphasis"><em>complete</em></span> tree
representing a <span class="emphasis"><em>single</em></span> location in the
repository at a single point in time:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="circle">
<li class="listitem">
<p>Don't use the <code class="option">--allow-mixed-revisions</code>
option to merge into mixed-revision working copies.</p>
</li>
<li class="listitem">
<p>Don't merge to targets with <span class="quote">“<span class="quote">switched</span>”</span>
subdirectories (as described next in
<a class="xref" href="svn.branchmerge.switchwc.html" title="Traversing Branches">the section called “Traversing Branches”</a>).</p>
</li>
<li class="listitem">
<p>Avoid merges to targets with sparse directories.
Likewise, don't merge to depths other than
<code class="option">--depth=infinity</code></p>
</li>
<li class="listitem">
<p>Be sure you have read access to all of the merge
source and read/write access to all of the merge
target.</p>
</li>
</ul>
</div>
<p>
</p>
</li>
</ul>
</div>
</div>
<div class="footnotes">
<br />
<hr width="100" align="left" />
<div class="footnote">
<p><sup>[<a id="ftn.idp11412560" href="#idp11412560" class="para">32</a>] </sup>At least, this is true in Subversion
1.7 at the time of this writing. This behavior may improve
in future versions of Subversion.</p>
</div>
<div class="footnote">
<p><sup>[<a id="ftn.idp11467760" href="#idp11467760" class="para">33</a>] </sup>Interestingly, after rolling
back a revision like this, we wouldn't be able to
reapply the revision using <strong class="userinput"><code>svn merge . -c
5</code></strong>, since the mergeinfo would already list r5
as being applied. We would have to use
the <code class="option">--ignore-ancestry</code> option to make
the merge command ignore the existing
mergeinfo!</p>
</div>
</div>
</div>
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<p>You are reading <em>Version Control with Subversion</em> (for Subversion 1.7), by Ben Collins-Sussman, Brian W. Fitzpatrick, and C. Michael Pilato.<br />
This work is licensed under the <a href="http://creativecommons.org/licenses/by/2.0/">Creative Commons Attribution License v2.0</a>.<br />
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