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[BOOK] Proposed warning about issue 895

From: Eric Hanchrow <offby1_at_blarg.net>
Date: 2004-10-31 20:46:01 CET

Last week I was bit by issue 895, and had to spend a fair amount of
time recovering by hand. I think I'd have saved time if I'd known
about that problem, and since it probably won't be fixed for a while,
it might be good to warn people about it. Therefore I've written such
a warning. I'd appreciate feedback.

* doc/book/book/ch04.xml
  (sect2 id="svn-ch-4-sect-3.2")
  Warn about issue 895

Index: ch04.xml
--- ch04.xml (revision 11683)
+++ ch04.xml (working copy)
@@ -869,6 +869,125 @@
+<!-- This is issue 895 (http://subversion.tigris.org/issues/show_bug.cgi?id=895) -->
+<!-- Delete this entire warning once that issue is fixed. -->
+ <warning>
+ <title>Avoid Restructuring Directories in a Branch</title>
+ <para>There's one thing that branches are
+ <emphasis>not</emphasis> good for: moving directories around.
+ Here's a simple example of what doesn't work the way you'd
+ expect: Suppose you have a project that looks like this:
+ <screen>
+ ... and you'd like to add a new directory
+ <filename>bar</filename>, and move
+ <filename>bar.c</filename> into it. So you create a branch
+ called <filename>big-directory-restructuring</filename> to
+ do your work, switch your working copy to that branch, and
+ then do
+$ svn mkdir bar
+A bar
+$ svn mv bar.c bar
+A bar/bar.c
+D bar.c
+$ svn ci -m "moved bar.c into new subdirectory 'bar'"
+Adding big-directory-restructuring/bar
+Adding big-directory-restructuring/bar/bar.c
+Deleting big-directory-restructuring/bar.c
+Committed revision 5.
+ So far, so good. But in the meantime, your co-worker has
+ made some edits to <filename>bar.c</filename> on the trunk,
+ and checked them in. <quote>That's OK</quote>, thinks you;
+ <quote>her changes and my move will conflict, and thus
+ there's no risk of any work being lost; I'll just resolve
+ the conflict when it happens</quote>. Think again. Here's
+ what happens: You switch back to the trunk, and merge in the
+ changes from the branch. You'll see this:
+$ svn up
+M bar.c
+$ svn merge -r4:5 http://svn.example.com/repos/calc/branches/big-directory-restructuring .
+A bar
+A bar/bar.c
+D bar.c
+$ svn ci -m "Unintentionally clobbering trunk changes"
+Adding trunk/bar
+Adding trunk/bar/bar.c
+Deleting trunk/bar.c
+Committed revision 7.
+ Now, guess what? Your co-worker's changes to
+ <filename>bar.c</filename>, which you just received via
+ <command>svn up</command>, are lost&mdash;file
+ <filename>bar.c</filename> was deleted, and replaced with
+ the version that was on the branch&mdash;<emphasis>and that
+ version doesn't contain her edits</emphasis>. Therefore you
+ <emphasis>have</emphasis> lost work, at least in the sense
+ that the work is no longer on the head of the trunk.
+ </para>
+ <para>
+ The only way that Your Obedient Servant knows to remedy this
+ situation, after the branch has been checked in, is to
+ review all the changes that were made on the trunk between
+ the creation of the branch and its merging, and reapply them
+ one at a time<footnote><para>You'll have to apply them one
+ at a time because each file is in a different directory in
+ your working copy than it was when the missing change was
+ applied.</para></footnote> to the trunk. For example:
+$ svn log -v http://svn.example.com/repos/calc
+r7 | erich | 2004-10-31 11:16:22 -0800 (Sun, 31 Oct 2004) | 1 line
+Changed paths:
+ A /trunk/bar (from /branches/big-directory-restructuring/bar:5)
+ D /trunk/bar.c
+Clobbering trunk changes
+r6 | erich | 2004-10-31 11:13:55 -0800 (Sun, 31 Oct 2004) | 1 line
+Changed paths:
+ M /trunk/bar.c
+*** empty log message ***
+r4 | erich | 2004-10-31 11:08:13 -0800 (Sun, 31 Oct 2004) | 1 line
+Changed paths:
+ A /branches/big-directory-restructuring (from /trunk:3)
+ In the example above, we see that the branch was created at
+ revision 4, and merged into the trunk at revision 7.
+ Therefore we need to reapply all changes to the trunk that
+ occurred between those revisions. In this example, that's
+ just revision 6:
+$ svn merge http://svn.example.com/repos/calc/trunk/bar.c@5 http://svn.example.com/repos/calc/trunk/bar.c@6 bar/bar.c
+U bar/bar.c
+$ svn ci -m "Reapplying changes that were clobbered at revision 7"
+Sending trunk/bar/bar.c
+Transmitting file data .
+Committed revision 9.
+ </para>
+ </warning>

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Received on Sun Oct 31 20:46:43 2004

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