git-svn: allow dcommit to retain local merge information

dcommit will still rewrite the HEAD commit and the history of the first
parents of each HEAD~1, HEAD~2, HEAD~3 as it always has.

However, any merge parents (HEAD^2, HEAD^^2, HEAD~2^2) will now be
preserved when the new HEAD and HEAD~[0-9]+ commits are rewritten to SVN
with dcommit.  Commits written to SVN will still not have any merge
information besides anything in the commit message.

Thanks to Joakim Tjernlund, Junio C Hamano and Steven Grimm
for explanations, feedback, examples and test case.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9114-git-svn-dcommit-merge.sh

@@ -0,0 +1,89 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Eric Wong
+# Based on a script by Joakim Tjernlund <joakim.tjernlund@transmode.se>
+
+test_description='git-svn dcommit handles merges'
+
+. ./lib-git-svn.sh
+
+big_text_block () {
+cat << EOF
+#
+# (C) Copyright 2000 - 2005
+# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+#
+# See file CREDITS for list of people who contributed to this
+# project.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation; either version 2 of
+# the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+# MA 02111-1307 USA
+#
+EOF
+}
+
+test_expect_success 'setup svn repository' "
+	svn co $svnrepo mysvnwork &&
+	mkdir -p mysvnwork/trunk &&
+	cd mysvnwork &&
+		big_text_block >> trunk/README &&
+		svn add trunk &&
+		svn ci -m 'first commit' trunk &&
+		cd ..
+	"
+
+test_expect_success 'setup git mirror and merge' "
+	git svn init $svnrepo -t tags -T trunk -b branches &&
+	git svn fetch &&
+	git checkout --track -b svn remotes/trunk &&
+	git checkout -b merge &&
+	echo new file > new_file &&
+	git add new_file &&
+	git commit -a -m 'New file' &&
+	echo hello >> README &&
+	git commit -a -m 'hello' &&
+	echo add some stuff >> new_file &&
+	git commit -a -m 'add some stuff' &&
+	git checkout svn &&
+	mv -f README tmp &&
+	echo friend > README &&
+	cat tmp >> README &&
+	git commit -a -m 'friend' &&
+	git pull . merge
+	"
+
+test_debug 'gitk --all & sleep 1'
+
+test_expect_success 'verify pre-merge ancestry' "
+	test x\`git rev-parse --verify refs/heads/svn^2\` = \
+	     x\`git rev-parse --verify refs/heads/merge\` &&
+	git cat-file commit refs/heads/svn^ | grep '^friend$'
+	"
+
+test_expect_success 'git svn dcommit merges' "
+	git svn dcommit
+	"
+
+test_debug 'gitk --all & sleep 1'
+
+test_expect_success 'verify post-merge ancestry' "
+	test x\`git rev-parse --verify refs/heads/svn\` = \
+	     x\`git rev-parse --verify refs/remotes/trunk \` &&
+	test x\`git rev-parse --verify refs/heads/svn^2\` = \
+	     x\`git rev-parse --verify refs/heads/merge\` &&
+	git cat-file commit refs/heads/svn^ | grep '^friend$'
+	"
+
+test_done