Add 'contrib/subtree/' from commit '2e63f75b8f49abe220ef55ec4e978e7a3b8dc351'dg/subtree

git-subtree-dir: contrib/subtree
git-subtree-mainline: c16df57c5a778ef14ede7ad202c74146269d61ac
git-subtree-split: 2e63f75b8f49abe220ef55ec4e978e7a3b8dc351

9 files changed, 2102 insertions, 0 deletions

diff --git a/contrib/subtree/.gitignore b/contrib/subtree/.gitignore
new file mode 100644
index 0000000000..7e77c9d022
--- /dev/null
+++ b/contrib/subtree/.gitignore
@@ -0,0 +1,5 @@
+*~
+git-subtree.xml
+git-subtree.1
+mainline
+subproj
diff --git a/contrib/subtree/COPYING b/contrib/subtree/COPYING
new file mode 100644
index 0000000000..d511905c16
--- /dev/null
+++ b/contrib/subtree/COPYING
@@ -0,0 +1,339 @@
+		    GNU GENERAL PUBLIC LICENSE
+		       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+			    Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+		    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
+    machine-readable copy of the corresponding source code, to be
+    distributed under the terms of Sections 1 and 2 above on a medium
+    customarily used for software interchange; or,
+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it.  For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+			    NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+		     END OF TERMS AND CONDITIONS
+
+	    How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    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.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/contrib/subtree/Makefile b/contrib/subtree/Makefile
new file mode 100644
index 0000000000..5568c9d5c8
--- /dev/null
+++ b/contrib/subtree/Makefile
@@ -0,0 +1,45 @@
+-include ../../config.mak.autogen
+-include ../../config.mak
+
+# this should be set to a 'standard' bsd-type install program
+INSTALL ?= install
+INSTALL_DATA = $(INSTALL) -c -m 0644
+INSTALL_EXE = $(INSTALL) -c -m 0755
+INSTALL_DIR = $(INSTALL) -c -d -m 0755
+
+ASCIIDOC_CONF      = ../../Documentation/asciidoc.conf
+MANPAGE_NORMAL_XSL =  ../../Documentation/manpage-normal.xsl
+
+GIT_SUBTREE_SH := git-subtree.sh
+GIT_SUBTREE    := ../../git-subtree
+
+all: $(GIT_SUBTREE)
+
+$(GIT_SUBTREE): $(GIT_SUBTREE_SH)
+	cp $< $@ && chmod +x $@
+
+install: install-exe install-doc
+
+install-exe: git-subtree.sh
+	$(INSTALL_DIR) $(DESTDIR)/$(gitdir)
+	$(INSTALL_EXE) $< $(DESTDIR)/$(gitdir)/git-subtree
+
+install-doc: git-subtree.1
+	$(INSTALL_DIR) $(DESTDIR)/$(mandir)/man1/
+	$(INSTALL_DATA) $< $(DESTDIR)/$(mandir)/man1/
+
+doc: git-subtree.1
+
+%.1: %.xml
+	xmlto -m $(MANPAGE_NORMAL)  man $^
+
+%.xml: %.txt
+	asciidoc -b docbook -d manpage -f $(ASCIIDOC_CONF) \
+		-agit_version=$(gitver) $^
+
+test:
+	$(MAKE) -C t/ all
+
+clean:
+	rm -f *~ *.xml *.html *.1
+	rm -rf subproj mainline
diff --git a/contrib/subtree/README b/contrib/subtree/README
new file mode 100644
index 0000000000..c686b4a69b
--- /dev/null
+++ b/contrib/subtree/README
@@ -0,0 +1,8 @@
+
+Please read git-subtree.txt for documentation.
+
+Please don't contact me using github mail; it's slow, ugly, and worst of
+all, redundant. Email me instead at apenwarr@gmail.com and I'll be happy to
+help.
+
+Avery
diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
new file mode 100755
index 0000000000..920c664bb7
--- /dev/null
+++ b/contrib/subtree/git-subtree.sh
@@ -0,0 +1,712 @@
+#!/bin/bash
+#
+# git-subtree.sh: split/join git repositories in subdirectories of this one
+#
+# Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
+#
+if [ $# -eq 0 ]; then
+    set -- -h
+fi
+OPTS_SPEC="\
+git subtree add   --prefix=<prefix> <commit>
+git subtree merge --prefix=<prefix> <commit>
+git subtree pull  --prefix=<prefix> <repository> <refspec...>
+git subtree push  --prefix=<prefix> <repository> <refspec...>
+git subtree split --prefix=<prefix> <commit...>
+--
+h,help        show the help
+q             quiet
+d             show debug messages
+P,prefix=     the name of the subdir to split out
+m,message=    use the given message as the commit message for the merge commit
+ options for 'split'
+annotate=     add a prefix to commit message of new commits
+b,branch=     create a new branch from the split subtree
+ignore-joins  ignore prior --rejoin commits
+onto=         try connecting new tree to an existing one
+rejoin        merge the new branch back into HEAD
+ options for 'add', 'merge', 'pull' and 'push'
+squash        merge subtree changes as a single commit
+"
+eval "$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
+
+PATH=$PATH:$(git --exec-path)
+. git-sh-setup
+
+require_work_tree
+
+quiet=
+branch=
+debug=
+command=
+onto=
+rejoin=
+ignore_joins=
+annotate=
+squash=
+message=
+
+debug()
+{
+	if [ -n "$debug" ]; then
+		echo "$@" >&2
+	fi
+}
+
+say()
+{
+	if [ -z "$quiet" ]; then
+		echo "$@" >&2
+	fi
+}
+
+assert()
+{
+	if "$@"; then
+		:
+	else
+		die "assertion failed: " "$@"
+	fi
+}
+
+
+#echo "Options: $*"
+
+while [ $# -gt 0 ]; do
+	opt="$1"
+	shift
+	case "$opt" in
+		-q) quiet=1 ;;
+		-d) debug=1 ;;
+		--annotate) annotate="$1"; shift ;;
+		--no-annotate) annotate= ;;
+		-b) branch="$1"; shift ;;
+		-P) prefix="$1"; shift ;;
+		-m) message="$1"; shift ;;
+		--no-prefix) prefix= ;;
+		--onto) onto="$1"; shift ;;
+		--no-onto) onto= ;;
+		--rejoin) rejoin=1 ;;
+		--no-rejoin) rejoin= ;;
+		--ignore-joins) ignore_joins=1 ;;
+		--no-ignore-joins) ignore_joins= ;;
+		--squash) squash=1 ;;
+		--no-squash) squash= ;;
+		--) break ;;
+		*) die "Unexpected option: $opt" ;;
+	esac
+done
+
+command="$1"
+shift
+case "$command" in
+	add|merge|pull) default= ;;
+	split|push) default="--default HEAD" ;;
+	*) die "Unknown command '$command'" ;;
+esac
+
+if [ -z "$prefix" ]; then
+	die "You must provide the --prefix option."
+fi
+
+case "$command" in
+	add) [ -e "$prefix" ] && 
+		die "prefix '$prefix' already exists." ;;
+	*)   [ -e "$prefix" ] || 
+		die "'$prefix' does not exist; use 'git subtree add'" ;;
+esac
+
+dir="$(dirname "$prefix/.")"
+
+if [ "$command" != "pull" -a "$command" != "add" -a "$command" != "push" ]; then
+	revs=$(git rev-parse $default --revs-only "$@") || exit $?
+	dirs="$(git rev-parse --no-revs --no-flags "$@")" || exit $?
+	if [ -n "$dirs" ]; then
+		die "Error: Use --prefix instead of bare filenames."
+	fi
+fi
+
+debug "command: {$command}"
+debug "quiet: {$quiet}"
+debug "revs: {$revs}"
+debug "dir: {$dir}"
+debug "opts: {$*}"
+debug
+
+cache_setup()
+{
+	cachedir="$GIT_DIR/subtree-cache/$$"
+	rm -rf "$cachedir" || die "Can't delete old cachedir: $cachedir"
+	mkdir -p "$cachedir" || die "Can't create new cachedir: $cachedir"
+	mkdir -p "$cachedir/notree" || die "Can't create new cachedir: $cachedir/notree"
+	debug "Using cachedir: $cachedir" >&2
+}
+
+cache_get()
+{
+	for oldrev in $*; do
+		if [ -r "$cachedir/$oldrev" ]; then
+			read newrev <"$cachedir/$oldrev"
+			echo $newrev
+		fi
+	done
+}
+
+cache_miss()
+{
+	for oldrev in $*; do
+		if [ ! -r "$cachedir/$oldrev" ]; then
+			echo $oldrev
+		fi
+	done
+}
+
+check_parents()
+{
+	missed=$(cache_miss $*)
+	for miss in $missed; do
+		if [ ! -r "$cachedir/notree/$miss" ]; then
+			debug "  incorrect order: $miss"
+		fi
+	done
+}
+
+set_notree()
+{
+	echo "1" > "$cachedir/notree/$1"
+}
+
+cache_set()
+{
+	oldrev="$1"
+	newrev="$2"
+	if [ "$oldrev" != "latest_old" \
+	     -a "$oldrev" != "latest_new" \
+	     -a -e "$cachedir/$oldrev" ]; then
+		die "cache for $oldrev already exists!"
+	fi
+	echo "$newrev" >"$cachedir/$oldrev"
+}
+
+rev_exists()
+{
+	if git rev-parse "$1" >/dev/null 2>&1; then
+		return 0
+	else
+		return 1
+	fi
+}
+
+rev_is_descendant_of_branch()
+{
+	newrev="$1"
+	branch="$2"
+	branch_hash=$(git rev-parse $branch)
+	match=$(git rev-list -1 $branch_hash ^$newrev)
+
+	if [ -z "$match" ]; then
+		return 0
+	else
+		return 1
+	fi
+}
+
+# if a commit doesn't have a parent, this might not work.  But we only want
+# to remove the parent from the rev-list, and since it doesn't exist, it won't
+# be there anyway, so do nothing in that case.
+try_remove_previous()
+{
+	if rev_exists "$1^"; then
+		echo "^$1^"
+	fi
+}
+
+find_latest_squash()
+{
+	debug "Looking for latest squash ($dir)..."
+	dir="$1"
+	sq=
+	main=
+	sub=
+	git log --grep="^git-subtree-dir: $dir/*\$" \
+		--pretty=format:'START %H%n%s%n%n%b%nEND%n' HEAD |
+	while read a b junk; do
+		debug "$a $b $junk"
+		debug "{{$sq/$main/$sub}}"
+		case "$a" in
+			START) sq="$b" ;;
+			git-subtree-mainline:) main="$b" ;;
+			git-subtree-split:) sub="$b" ;;
+			END)
+				if [ -n "$sub" ]; then
+					if [ -n "$main" ]; then
+						# a rejoin commit?
+						# Pretend its sub was a squash.
+						sq="$sub"
+					fi
+					debug "Squash found: $sq $sub"
+					echo "$sq" "$sub"
+					break
+				fi
+				sq=
+				main=
+				sub=
+				;;
+		esac
+	done
+}
+
+find_existing_splits()
+{
+	debug "Looking for prior splits..."
+	dir="$1"
+	revs="$2"
+	main=
+	sub=
+	git log --grep="^git-subtree-dir: $dir/*\$" \
+		--pretty=format:'START %H%n%s%n%n%b%nEND%n' $revs |
+	while read a b junk; do
+		case "$a" in
+			START) sq="$b" ;;
+			git-subtree-mainline:) main="$b" ;;
+			git-subtree-split:) sub="$b" ;;
+			END)
+				debug "  Main is: '$main'"
+				if [ -z "$main" -a -n "$sub" ]; then
+					# squash commits refer to a subtree
+					debug "  Squash: $sq from $sub"
+					cache_set "$sq" "$sub"
+				fi
+				if [ -n "$main" -a -n "$sub" ]; then
+					debug "  Prior: $main -> $sub"
+					cache_set $main $sub
+					cache_set $sub $sub
+					try_remove_previous "$main"
+					try_remove_previous "$sub"
+				fi
+				main=
+				sub=
+				;;
+		esac
+	done
+}
+
+copy_commit()
+{
+	# We're going to set some environment vars here, so
+	# do it in a subshell to get rid of them safely later
+	debug copy_commit "{$1}" "{$2}" "{$3}"
+	git log -1 --pretty=format:'%an%n%ae%n%ad%n%cn%n%ce%n%cd%n%s%n%n%b' "$1" |
+	(
+		read GIT_AUTHOR_NAME
+		read GIT_AUTHOR_EMAIL
+		read GIT_AUTHOR_DATE
+		read GIT_COMMITTER_NAME
+		read GIT_COMMITTER_EMAIL
+		read GIT_COMMITTER_DATE
+		export  GIT_AUTHOR_NAME \
+			GIT_AUTHOR_EMAIL \
+			GIT_AUTHOR_DATE \
+			GIT_COMMITTER_NAME \
+			GIT_COMMITTER_EMAIL \
+			GIT_COMMITTER_DATE
+		(echo -n "$annotate"; cat ) |
+		git commit-tree "$2" $3  # reads the rest of stdin
+	) || die "Can't copy commit $1"
+}
+
+add_msg()
+{
+	dir="$1"
+	latest_old="$2"
+	latest_new="$3"
+	if [ -n "$message" ]; then
+		commit_message="$message"
+	else
+		commit_message="Add '$dir/' from commit '$latest_new'"
+	fi
+	cat <<-EOF
+		$commit_message
+		
+		git-subtree-dir: $dir
+		git-subtree-mainline: $latest_old
+		git-subtree-split: $latest_new
+	EOF
+}
+
+add_squashed_msg()
+{
+	if [ -n "$message" ]; then
+		echo "$message"
+	else
+		echo "Merge commit '$1' as '$2'"
+	fi
+}
+
+rejoin_msg()
+{
+	dir="$1"
+	latest_old="$2"
+	latest_new="$3"
+	if [ -n "$message" ]; then
+		commit_message="$message"
+	else
+		commit_message="Split '$dir/' into commit '$latest_new'"
+	fi
+	cat <<-EOF
+		$commit_message
+		
+		git-subtree-dir: $dir
+		git-subtree-mainline: $latest_old
+		git-subtree-split: $latest_new
+	EOF
+}
+
+squash_msg()
+{
+	dir="$1"
+	oldsub="$2"
+	newsub="$3"
+	newsub_short=$(git rev-parse --short "$newsub")
+	
+	if [ -n "$oldsub" ]; then
+		oldsub_short=$(git rev-parse --short "$oldsub")
+		echo "Squashed '$dir/' changes from $oldsub_short..$newsub_short"
+		echo
+		git log --pretty=tformat:'%h %s' "$oldsub..$newsub"
+		git log --pretty=tformat:'REVERT: %h %s' "$newsub..$oldsub"
+	else
+		echo "Squashed '$dir/' content from commit $newsub_short"
+	fi
+	
+	echo
+	echo "git-subtree-dir: $dir"
+	echo "git-subtree-split: $newsub"
+}
+
+toptree_for_commit()
+{
+	commit="$1"
+	git log -1 --pretty=format:'%T' "$commit" -- || exit $?
+}
+
+subtree_for_commit()
+{
+	commit="$1"
+	dir="$2"
+	git ls-tree "$commit" -- "$dir" |
+	while read mode type tree name; do
+		assert [ "$name" = "$dir" ]
+		assert [ "$type" = "tree" -o "$type" = "commit" ]
+		[ "$type" = "commit" ] && continue  # ignore submodules
+		echo $tree
+		break
+	done
+}
+
+tree_changed()
+{
+	tree=$1
+	shift
+	if [ $# -ne 1 ]; then
+		return 0   # weird parents, consider it changed
+	else
+		ptree=$(toptree_for_commit $1)
+		if [ "$ptree" != "$tree" ]; then
+			return 0   # changed
+		else
+			return 1   # not changed
+		fi
+	fi
+}
+
+new_squash_commit()
+{
+	old="$1"
+	oldsub="$2"
+	newsub="$3"
+	tree=$(toptree_for_commit $newsub) || exit $?
+	if [ -n "$old" ]; then
+		squash_msg "$dir" "$oldsub" "$newsub" | 
+			git commit-tree "$tree" -p "$old" || exit $?
+	else
+		squash_msg "$dir" "" "$newsub" |
+			git commit-tree "$tree" || exit $?
+	fi
+}
+
+copy_or_skip()
+{
+	rev="$1"
+	tree="$2"
+	newparents="$3"
+	assert [ -n "$tree" ]
+
+	identical=
+	nonidentical=
+	p=
+	gotparents=
+	for parent in $newparents; do
+		ptree=$(toptree_for_commit $parent) || exit $?
+		[ -z "$ptree" ] && continue
+		if [ "$ptree" = "$tree" ]; then
+			# an identical parent could be used in place of this rev.
+			identical="$parent"
+		else
+			nonidentical="$parent"
+		fi
+		
+		# sometimes both old parents map to the same newparent;
+		# eliminate duplicates
+		is_new=1
+		for gp in $gotparents; do
+			if [ "$gp" = "$parent" ]; then
+				is_new=
+				break
+			fi
+		done
+		if [ -n "$is_new" ]; then
+			gotparents="$gotparents $parent"
+			p="$p -p $parent"
+		fi
+	done
+	
+	if [ -n "$identical" ]; then
+		echo $identical
+	else
+		copy_commit $rev $tree "$p" || exit $?
+	fi
+}
+
+ensure_clean()
+{
+	if ! git diff-index HEAD --exit-code --quiet 2>&1; then
+		die "Working tree has modifications.  Cannot add."
+	fi
+	if ! git diff-index --cached HEAD --exit-code --quiet 2>&1; then
+		die "Index has modifications.  Cannot add."
+	fi
+}
+
+cmd_add()
+{
+	if [ -e "$dir" ]; then
+		die "'$dir' already exists.  Cannot add."
+	fi
+
+	ensure_clean
+	
+	if [ $# -eq 1 ]; then
+		"cmd_add_commit" "$@"
+	elif [ $# -eq 2 ]; then
+		"cmd_add_repository" "$@"
+	else
+	    say "error: parameters were '$@'"
+	    die "Provide either a refspec or a repository and refspec."
+	fi
+}
+
+cmd_add_repository()
+{
+	echo "git fetch" "$@"
+	repository=$1
+	refspec=$2
+	git fetch "$@" || exit $?
+	revs=FETCH_HEAD
+	set -- $revs
+	cmd_add_commit "$@"
+}
+
+cmd_add_commit()
+{
+	revs=$(git rev-parse $default --revs-only "$@") || exit $?
+	set -- $revs
+	rev="$1"
+	
+	debug "Adding $dir as '$rev'..."
+	git read-tree --prefix="$dir" $rev || exit $?
+	git checkout -- "$dir" || exit $?
+	tree=$(git write-tree) || exit $?
+	
+	headrev=$(git rev-parse HEAD) || exit $?
+	if [ -n "$headrev" -a "$headrev" != "$rev" ]; then
+		headp="-p $headrev"
+	else
+		headp=
+	fi
+	
+	if [ -n "$squash" ]; then
+		rev=$(new_squash_commit "" "" "$rev") || exit $?
+		commit=$(add_squashed_msg "$rev" "$dir" |
+			 git commit-tree $tree $headp -p "$rev") || exit $?
+	else
+		commit=$(add_msg "$dir" "$headrev" "$rev" |
+			 git commit-tree $tree $headp -p "$rev") || exit $?
+	fi
+	git reset "$commit" || exit $?
+	
+	say "Added dir '$dir'"
+}
+
+cmd_split()
+{
+	debug "Splitting $dir..."
+	cache_setup || exit $?
+	
+	if [ -n "$onto" ]; then
+		debug "Reading history for --onto=$onto..."
+		git rev-list $onto |
+		while read rev; do
+			# the 'onto' history is already just the subdir, so
+			# any parent we find there can be used verbatim
+			debug "  cache: $rev"
+			cache_set $rev $rev
+		done
+	fi
+	
+	if [ -n "$ignore_joins" ]; then
+		unrevs=
+	else
+		unrevs="$(find_existing_splits "$dir" "$revs")"
+	fi
+	
+	# We can't restrict rev-list to only $dir here, because some of our
+	# parents have the $dir contents the root, and those won't match.
+	# (and rev-list --follow doesn't seem to solve this)
+	grl='git rev-list --topo-order --reverse --parents $revs $unrevs'
+	revmax=$(eval "$grl" | wc -l)
+	revcount=0
+	createcount=0
+	eval "$grl" |
+	while read rev parents; do
+		revcount=$(($revcount + 1))
+		say -n "$revcount/$revmax ($createcount)
"
+		debug "Processing commit: $rev"
+		exists=$(cache_get $rev)
+		if [ -n "$exists" ]; then
+			debug "  prior: $exists"
+			continue
+		fi
+		createcount=$(($createcount + 1))
+		debug "  parents: $parents"
+		newparents=$(cache_get $parents)
+		debug "  newparents: $newparents"
+		
+		tree=$(subtree_for_commit $rev "$dir")
+		debug "  tree is: $tree"
+
+		check_parents $parents
+		
+		# ugly.  is there no better way to tell if this is a subtree
+		# vs. a mainline commit?  Does it matter?
+		if [ -z $tree ]; then
+			set_notree $rev
+			if [ -n "$newparents" ]; then
+				cache_set $rev $rev
+			fi
+			continue
+		fi
+
+		newrev=$(copy_or_skip "$rev" "$tree" "$newparents") || exit $?
+		debug "  newrev is: $newrev"
+		cache_set $rev $newrev
+		cache_set latest_new $newrev
+		cache_set latest_old $rev
+	done || exit $?
+	latest_new=$(cache_get latest_new)
+	if [ -z "$latest_new" ]; then
+		die "No new revisions were found"
+	fi
+	
+	if [ -n "$rejoin" ]; then
+		debug "Merging split branch into HEAD..."
+		latest_old=$(cache_get latest_old)
+		git merge -s ours \
+			-m "$(rejoin_msg $dir $latest_old $latest_new)" \
+			$latest_new >&2 || exit $?
+	fi
+	if [ -n "$branch" ]; then
+		if rev_exists "refs/heads/$branch"; then
+			if ! rev_is_descendant_of_branch $latest_new $branch; then
+				die "Branch '$branch' is not an ancestor of commit '$latest_new'."
+			fi
+			action='Updated'
+		else
+			action='Created'
+		fi
+		git update-ref -m 'subtree split' "refs/heads/$branch" $latest_new || exit $?
+		say "$action branch '$branch'"
+	fi
+	echo $latest_new
+	exit 0
+}
+
+cmd_merge()
+{
+	revs=$(git rev-parse $default --revs-only "$@") || exit $?
+	ensure_clean
+	
+	set -- $revs
+	if [ $# -ne 1 ]; then
+		die "You must provide exactly one revision.  Got: '$revs'"
+	fi
+	rev="$1"
+	
+	if [ -n "$squash" ]; then
+		first_split="$(find_latest_squash "$dir")"
+		if [ -z "$first_split" ]; then
+			die "Can't squash-merge: '$dir' was never added."
+		fi
+		set $first_split
+		old=$1
+		sub=$2
+		if [ "$sub" = "$rev" ]; then
+			say "Subtree is already at commit $rev."
+			exit 0
+		fi
+		new=$(new_squash_commit "$old" "$sub" "$rev") || exit $?
+		debug "New squash commit: $new"
+		rev="$new"
+	fi
+
+	version=$(git version)
+	if [ "$version" \< "git version 1.7" ]; then
+		if [ -n "$message" ]; then
+			git merge -s subtree --message="$message" $rev
+		else
+			git merge -s subtree $rev
+		fi
+	else
+		if [ -n "$message" ]; then
+			git merge -Xsubtree="$prefix" --message="$message" $rev
+		else
+			git merge -Xsubtree="$prefix" $rev
+		fi
+	fi
+}
+
+cmd_pull()
+{
+	ensure_clean
+	git fetch "$@" || exit $?
+	revs=FETCH_HEAD
+	set -- $revs
+	cmd_merge "$@"
+}
+
+cmd_push()
+{
+	if [ $# -ne 2 ]; then
+	    die "You must provide <repository> <refspec>"
+	fi
+	if [ -e "$dir" ]; then
+	    repository=$1
+	    refspec=$2
+	    echo "git push using: " $repository $refspec
+	    git push $repository $(git subtree split --prefix=$prefix):refs/heads/$refspec
+	else
+	    die "'$dir' must already exist. Try 'git subtree add'."
+	fi
+}
+
+"cmd_$command" "$@"
diff --git a/contrib/subtree/git-subtree.txt b/contrib/subtree/git-subtree.txt
new file mode 100644
index 0000000000..0c44fda011
--- /dev/null
+++ b/contrib/subtree/git-subtree.txt
@@ -0,0 +1,366 @@
+git-subtree(1)
+==============
+
+NAME
+----
+git-subtree - Merge subtrees together and split repository into subtrees
+
+
+SYNOPSIS
+--------
+[verse]
+'git subtree' add   -P <prefix> <commit>
+'git subtree' pull  -P <prefix> <repository> <refspec...>
+'git subtree' push  -P <prefix> <repository> <refspec...>
+'git subtree' merge -P <prefix> <commit>
+'git subtree' split -P <prefix> [OPTIONS] [<commit>]
+
+
+DESCRIPTION
+-----------
+Subtrees allow subprojects to be included within a subdirectory
+of the main project, optionally including the subproject's
+entire history.
+
+For example, you could include the source code for a library
+as a subdirectory of your application.
+
+Subtrees are not to be confused with submodules, which are meant for
+the same task. Unlike submodules, subtrees do not need any special
+constructions (like .gitmodule files or gitlinks) be present in
+your repository, and do not force end-users of your
+repository to do anything special or to understand how subtrees
+work. A subtree is just a subdirectory that can be
+committed to, branched, and merged along with your project in
+any way you want.
+
+They are also not to be confused with using the subtree merge
+strategy. The main difference is that, besides merging
+the other project as a subdirectory, you can also extract the
+entire history of a subdirectory from your project and make it
+into a standalone project. Unlike the subtree merge strategy
+you can alternate back and forth between these
+two operations. If the standalone library gets updated, you can
+automatically merge the changes into your project; if you
+update the library inside your project, you can "split" the
+changes back out again and merge them back into the library
+project.
+
+For example, if a library you made for one application ends up being
+useful elsewhere, you can extract its entire history and publish
+that as its own git repository, without accidentally
+intermingling the history of your application project.
+
+[TIP]
+In order to keep your commit messages clean, we recommend that
+people split their commits between the subtrees and the main
+project as much as possible.  That is, if you make a change that
+affects both the library and the main application, commit it in
+two pieces.  That way, when you split the library commits out
+later, their descriptions will still make sense.  But if this
+isn't important to you, it's not *necessary*.  git subtree will
+simply leave out the non-library-related parts of the commit
+when it splits it out into the subproject later.
+
+
+COMMANDS
+--------
+add::
+	Create the <prefix> subtree by importing its contents
+	from the given <refspec> or <repository> and remote <refspec>.
+	A new commit is created	automatically, joining the imported
+	project's history with your own.  With '--squash', imports
+	only a single commit from the subproject, rather than its
+	entire history.
+
+merge::
+	Merge recent changes up to <commit> into the <prefix>
+	subtree.  As with normal 'git merge', this doesn't
+	remove your own local changes; it just merges those
+	changes into the latest <commit>.  With '--squash',
+	creates only one commit that contains all the changes,
+	rather than merging in the entire history.
+
+	If you use '--squash', the merge direction doesn't
+	always have to be forward; you can use this command to
+	go back in time from v2.5 to v2.4, for example.  If your
+	merge introduces a conflict, you can resolve it in the
+	usual ways.
+	
+pull::
+	Exactly like 'merge', but parallels 'git pull' in that
+	it fetches the given commit from the specified remote
+	repository.
+	
+push::
+	Does a 'split' (see above) using the <prefix> supplied
+	and then does a 'git push' to push the result to the 
+	repository and refspec. This can be used to push your
+	subtree to different branches of the remote repository.
+
+split::
+	Extract a new, synthetic project history from the
+	history of the <prefix> subtree.  The new history
+	includes only the commits (including merges) that
+	affected <prefix>, and each of those commits now has the
+	contents of <prefix> at the root of the project instead
+	of in a subdirectory.  Thus, the newly created history
+	is suitable for export as a separate git repository.
+	
+	After splitting successfully, a single commit id is
+	printed to stdout.  This corresponds to the HEAD of the
+	newly created tree, which you can manipulate however you
+	want.
+	
+	Repeated splits of exactly the same history are
+	guaranteed to be identical (ie. to produce the same
+	commit ids).  Because of this, if you add new commits
+	and then re-split, the new commits will be attached as
+	commits on top of the history you generated last time,
+	so 'git merge' and friends will work as expected.
+	
+	Note that if you use '--squash' when you merge, you
+	should usually not just '--rejoin' when you split.
+
+
+OPTIONS
+-------
+-q::
+--quiet::
+	Suppress unnecessary output messages on stderr.
+
+-d::
+--debug::
+	Produce even more unnecessary output messages on stderr.
+
+-P <prefix>::
+--prefix=<prefix>::
+	Specify the path in the repository to the subtree you
+	want to manipulate.  This option is mandatory
+	for all commands.
+
+-m <message>::
+--message=<message>::
+	This option is only valid for add, merge and pull (unsure).
+	Specify <message> as the commit message for the merge commit.
+
+
+OPTIONS FOR add, merge, push, pull
+----------------------------------
+--squash::
+	This option is only valid for add, merge, push and pull
+	commands.
+
+	Instead of merging the entire history from the subtree
+	project, produce only a single commit that contains all
+	the differences you want to merge, and then merge that
+	new commit into your project.
+	
+	Using this option helps to reduce log clutter. People
+	rarely want to see every change that happened between
+	v1.0 and v1.1 of the library they're using, since none of the
+	interim versions were ever included in their application.
+	
+	Using '--squash' also helps avoid problems when the same
+	subproject is included multiple times in the same
+	project, or is removed and then re-added.  In such a
+	case, it doesn't make sense to combine the histories
+	anyway, since it's unclear which part of the history
+	belongs to which subtree.
+	
+	Furthermore, with '--squash', you can switch back and
+	forth between different versions of a subtree, rather
+	than strictly forward.  'git subtree merge --squash'
+	always adjusts the subtree to match the exactly
+	specified commit, even if getting to that commit would
+	require undoing some changes that were added earlier.
+	
+	Whether or not you use '--squash', changes made in your
+	local repository remain intact and can be later split
+	and send upstream to the subproject.
+
+
+OPTIONS FOR split
+-----------------
+--annotate=<annotation>::
+	This option is only valid for the split command.
+
+	When generating synthetic history, add <annotation> as a
+	prefix to each commit message.  Since we're creating new
+	commits with the same commit message, but possibly
+	different content, from the original commits, this can help
+	to differentiate them and avoid confusion.
+	
+	Whenever you split, you need to use the same
+	<annotation>, or else you don't have a guarantee that
+	the new re-created history will be identical to the old
+	one.  That will prevent merging from working correctly. 
+	git subtree tries to make it work anyway, particularly
+	if you use --rejoin, but it may not always be effective.
+
+-b <branch>::
+--branch=<branch>::
+	This option is only valid for the split command.
+
+	After generating the synthetic history, create a new
+	branch called <branch> that contains the new history. 
+	This is suitable for immediate pushing upstream. 
+	<branch> must not already exist.
+
+--ignore-joins::
+	This option is only valid for the split command.
+
+	If you use '--rejoin', git subtree attempts to optimize
+	its history reconstruction to generate only the new
+	commits since the last '--rejoin'.  '--ignore-join'
+	disables this behaviour, forcing it to regenerate the
+	entire history.  In a large project, this can take a
+	long time.
+
+--onto=<onto>::
+	This option is only valid for the split command.
+
+	If your subtree was originally imported using something
+	other than git subtree, its history may not match what
+	git subtree is expecting.  In that case, you can specify
+	the commit id <onto> that corresponds to the first
+	revision of the subproject's history that was imported
+	into your project, and git subtree will attempt to build
+	its history from there.
+	
+	If you used 'git subtree add', you should never need
+	this option.
+
+--rejoin::
+	This option is only valid for the split command.
+
+	After splitting, merge the newly created synthetic
+	history back into your main project.  That way, future
+	splits can search only the part of history that has
+	been added since the most recent --rejoin.
+	
+	If your split commits end up merged into the upstream
+	subproject, and then you want to get the latest upstream
+	version, this will allow git's merge algorithm to more
+	intelligently avoid conflicts (since it knows these
+	synthetic commits are already part of the upstream
+	repository).
+	
+	Unfortunately, using this option results in 'git log'
+	showing an extra copy of every new commit that was
+	created (the original, and the synthetic one).
+	
+	If you do all your merges with '--squash', don't use
+	'--rejoin' when you split, because you don't want the
+	subproject's history to be part of your project anyway.
+
+
+EXAMPLE 1. Add command
+----------------------
+Let's assume that you have a local repository that you would like
+to add an external vendor library to. In this case we will add the
+git-subtree repository as a subdirectory of your already existing
+git-extensions repository in ~/git-extensions/:
+
+	$ git subtree add --prefix=git-subtree --squash \
+		git://github.com/apenwarr/git-subtree.git master
+
+'master' needs to be a valid remote ref and can be a different branch
+name
+
+You can omit the --squash flag, but doing so will increase the number
+of commits that are incldued in your local repository.
+
+We now have a ~/git-extensions/git-subtree directory containing code
+from the master branch of git://github.com/apenwarr/git-subtree.git
+in our git-extensions repository.
+
+EXAMPLE 2. Extract a subtree using commit, merge and pull
+---------------------------------------------------------
+Let's use the repository for the git source code as an example.
+First, get your own copy of the git.git repository:
+
+	$ git clone git://git.kernel.org/pub/scm/git/git.git test-git
+	$ cd test-git
+
+gitweb (commit 1130ef3) was merged into git as of commit
+0a8f4f0, after which it was no longer maintained separately. 
+But imagine it had been maintained separately, and we wanted to
+extract git's changes to gitweb since that time, to share with
+the upstream.  You could do this:
+
+	$ git subtree split --prefix=gitweb --annotate='(split) ' \
+        	0a8f4f0^.. --onto=1130ef3 --rejoin \
+        	--branch gitweb-latest
+        $ gitk gitweb-latest
+        $ git push git@github.com:whatever/gitweb.git gitweb-latest:master
+        
+(We use '0a8f4f0^..' because that means "all the changes from
+0a8f4f0 to the current version, including 0a8f4f0 itself.")
+
+If gitweb had originally been merged using 'git subtree add' (or
+a previous split had already been done with --rejoin specified)
+then you can do all your splits without having to remember any
+weird commit ids:
+
+	$ git subtree split --prefix=gitweb --annotate='(split) ' --rejoin \
+		--branch gitweb-latest2
+
+And you can merge changes back in from the upstream project just
+as easily:
+
+	$ git subtree pull --prefix=gitweb \
+		git@github.com:whatever/gitweb.git master
+
+Or, using '--squash', you can actually rewind to an earlier
+version of gitweb:
+
+	$ git subtree merge --prefix=gitweb --squash gitweb-latest~10
+
+Then make some changes:
+
+	$ date >gitweb/myfile
+	$ git add gitweb/myfile
+	$ git commit -m 'created myfile'
+
+And fast forward again:
+
+	$ git subtree merge --prefix=gitweb --squash gitweb-latest
+
+And notice that your change is still intact:
+	
+	$ ls -l gitweb/myfile
+
+And you can split it out and look at your changes versus
+the standard gitweb:
+
+	git log gitweb-latest..$(git subtree split --prefix=gitweb)
+
+EXAMPLE 3. Extract a subtree using branch
+-----------------------------------------
+Suppose you have a source directory with many files and
+subdirectories, and you want to extract the lib directory to its own
+git project. Here's a short way to do it:
+
+First, make the new repository wherever you want:
+
+	$ <go to the new location>
+	$ git init --bare
+
+Back in your original directory:
+
+	$ git subtree split --prefix=lib --annotate="(split)" -b split
+
+Then push the new branch onto the new empty repository:
+
+	$ git push <new-repo> split:master
+
+
+AUTHOR
+------
+Written by Avery Pennarun <apenwarr@gmail.com>
+
+
+GIT
+---
+Part of the linkgit:git[1] suite
diff --git a/contrib/subtree/t/Makefile b/contrib/subtree/t/Makefile
new file mode 100644
index 0000000000..c864810389
--- /dev/null
+++ b/contrib/subtree/t/Makefile
@@ -0,0 +1,69 @@
+# Run tests
+#
+# Copyright (c) 2005 Junio C Hamano
+#
+
+-include ../../../config.mak.autogen
+-include ../../../config.mak
+
+#GIT_TEST_OPTS=--verbose --debug
+SHELL_PATH ?= $(SHELL)
+PERL_PATH ?= /usr/bin/perl
+TAR ?= $(TAR)
+RM ?= rm -f
+PROVE ?= prove
+DEFAULT_TEST_TARGET ?= test
+
+# Shell quote;
+SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
+
+T = $(wildcard t[0-9][0-9][0-9][0-9]-*.sh)
+
+all: $(DEFAULT_TEST_TARGET)
+
+test: pre-clean $(TEST_LINT)
+	$(MAKE) aggregate-results-and-cleanup
+
+prove: pre-clean $(TEST_LINT)
+	@echo "*** prove ***"; GIT_CONFIG=.git/config $(PROVE) --exec '$(SHELL_PATH_SQ)' $(GIT_PROVE_OPTS) $(T) :: $(GIT_TEST_OPTS)
+	$(MAKE) clean
+
+$(T):
+	@echo "*** $@ ***"; GIT_CONFIG=.git/config '$(SHELL_PATH_SQ)' $@ $(GIT_TEST_OPTS)
+
+pre-clean:
+	$(RM) -r test-results
+
+clean:
+	$(RM) -r 'trash directory'.* test-results
+	$(RM) -r valgrind/bin
+	$(RM) .prove
+
+test-lint: test-lint-duplicates test-lint-executable
+
+test-lint-duplicates:
+	@dups=`echo $(T) | tr ' ' '\n' | sed 's/-.*//' | sort | uniq -d` && \
+		test -z "$$dups" || { \
+		echo >&2 "duplicate test numbers:" $$dups; exit 1; }
+
+test-lint-executable:
+	@bad=`for i in $(T); do test -x "$$i" || echo $$i; done` && \
+		test -z "$$bad" || { \
+		echo >&2 "non-executable tests:" $$bad; exit 1; }
+
+aggregate-results-and-cleanup: $(T)
+	$(MAKE) aggregate-results
+	$(MAKE) clean
+
+aggregate-results:
+	for f in ../../../t/test-results/t*-*.counts; do \
+		echo "$$f"; \
+	done | '$(SHELL_PATH_SQ)' ../../../t/aggregate-results.sh
+
+valgrind:
+	$(MAKE) GIT_TEST_OPTS="$(GIT_TEST_OPTS) --valgrind"
+
+test-results:
+	mkdir -p test-results
+
+.PHONY: pre-clean $(T) aggregate-results clean valgrind
diff --git a/contrib/subtree/t/t7900-subtree.sh b/contrib/subtree/t/t7900-subtree.sh
new file mode 100755
index 0000000000..bc2eeb0944
--- /dev/null
+++ b/contrib/subtree/t/t7900-subtree.sh
@@ -0,0 +1,508 @@
+#!/bin/sh
+#
+# Copyright (c) 2012 Avery Pennaraum
+#
+test_description='Basic porcelain support for subtrees
+
+This test verifies the basic operation of the merge, pull, add
+and split subcommands of git subtree.
+'
+
+export TEST_DIRECTORY=$(pwd)/../../../t
+
+. ../../../t/test-lib.sh
+
+create()
+{
+	echo "$1" >"$1"
+	git add "$1"
+}
+
+
+check_equal()
+{
+	test_debug 'echo'
+	test_debug "echo \"check a:\" \"{$1}\""
+	test_debug "echo \"      b:\" \"{$2}\""
+	if [ "$1" = "$2" ]; then
+		return 0
+	else
+		return 1
+	fi
+}
+
+fixnl()
+{
+	t=""
+	while read x; do
+		t="$t$x "
+	done
+	echo $t
+}
+
+multiline()
+{
+	while read x; do
+		set -- $x
+		for d in "$@"; do
+			echo "$d"
+		done
+	done
+}
+
+undo()
+{
+	git reset --hard HEAD~
+}
+
+last_commit_message()
+{
+	git log --pretty=format:%s -1
+}
+
+# 1
+test_expect_success 'init subproj' '
+        test_create_repo subproj
+'
+
+# To the subproject!
+cd subproj
+
+# 2
+test_expect_success 'add sub1' '
+        create sub1 &&
+        git commit -m "sub1" &&
+        git branch sub1 &&
+        git branch -m master subproj
+'
+
+# 3
+test_expect_success 'add sub2' '
+        create sub2 &&
+        git commit -m "sub2" &&
+        git branch sub2
+'
+
+# 4
+test_expect_success 'add sub3' '
+        create sub3 &&
+        git commit -m "sub3" &&
+        git branch sub3
+'
+
+# Back to mainline
+cd ..
+
+# 5
+test_expect_success 'add main4' '
+        create main4 &&
+        git commit -m "main4" &&
+        git branch -m master mainline &&
+        git branch subdir
+'
+
+# 6
+test_expect_success 'fetch subproj history' '
+        git fetch ./subproj sub1 &&
+        git branch sub1 FETCH_HEAD
+'
+
+# 7
+test_expect_success 'no subtree exists in main tree' '
+        test_must_fail git subtree merge --prefix=subdir sub1
+'
+
+# 8
+test_expect_success 'no pull from non-existant subtree' '
+        test_must_fail git subtree pull --prefix=subdir ./subproj sub1
+'
+
+# 9
+test_expect_success 'check if --message works for add' '
+        git subtree add --prefix=subdir --message="Added subproject" sub1 &&
+        check_equal ''"$(last_commit_message)"'' "Added subproject" &&
+        undo
+'
+
+# 10
+test_expect_success 'check if --message works as -m and --prefix as -P' '
+        git subtree add -P subdir -m "Added subproject using git subtree" sub1 &&
+        check_equal ''"$(last_commit_message)"'' "Added subproject using git subtree" &&
+        undo
+'
+
+# 11
+test_expect_success 'check if --message works with squash too' '
+        git subtree add -P subdir -m "Added subproject with squash" --squash sub1 &&
+        check_equal ''"$(last_commit_message)"'' "Added subproject with squash" &&
+        undo
+'
+
+# 12
+test_expect_success 'add subproj to mainline' '
+        git subtree add --prefix=subdir/ FETCH_HEAD &&
+        check_equal ''"$(last_commit_message)"'' "Add '"'subdir/'"' from commit '"'"'''"$(git rev-parse sub1)"'''"'"'"
+'
+
+# 13
+# this shouldn't actually do anything, since FETCH_HEAD is already a parent
+test_expect_success 'merge fetched subproj' '
+        git merge -m "merge -s -ours" -s ours FETCH_HEAD
+'
+
+# 14
+test_expect_success 'add main-sub5' '
+        create subdir/main-sub5 &&
+        git commit -m "main-sub5"
+'
+
+# 15
+test_expect_success 'add main6' '
+        create main6 &&
+        git commit -m "main6 boring"
+'
+
+# 16
+test_expect_success 'add main-sub7' '
+        create subdir/main-sub7 &&
+        git commit -m "main-sub7"
+'
+
+# 17
+test_expect_success 'fetch new subproj history' '
+        git fetch ./subproj sub2 &&
+        git branch sub2 FETCH_HEAD
+'
+
+# 18
+test_expect_success 'check if --message works for merge' '
+        git subtree merge --prefix=subdir -m "Merged changes from subproject" sub2 &&
+        check_equal ''"$(last_commit_message)"'' "Merged changes from subproject" &&
+        undo
+'
+
+# 19
+test_expect_success 'check if --message for merge works with squash too' '
+        git subtree merge --prefix subdir -m "Merged changes from subproject using squash" --squash sub2 &&
+        check_equal ''"$(last_commit_message)"'' "Merged changes from subproject using squash" &&
+        undo
+'
+
+# 20
+test_expect_success 'merge new subproj history into subdir' '
+        git subtree merge --prefix=subdir FETCH_HEAD &&
+        git branch pre-split &&
+        check_equal ''"$(last_commit_message)"'' "Merge commit '"'"'"$(git rev-parse sub2)"'"'"' into mainline"
+'
+
+# 21
+test_expect_success 'Check that prefix argument is required for split' '
+        echo "You must provide the --prefix option." > expected &&
+        test_must_fail git subtree split > actual 2>&1 &&
+        test_debug "echo -n expected: " &&
+        test_debug "cat expected" &&
+        test_debug "echo -n actual: " &&
+        test_debug "cat actual" &&
+        test_cmp expected actual &&
+        rm -f expected actual
+'
+
+# 22
+test_expect_success 'Check that the <prefix> exists for a split' '
+        echo "'"'"'non-existent-directory'"'"'" does not exist\; use "'"'"'git subtree add'"'"'" > expected &&
+        test_must_fail git subtree split --prefix=non-existent-directory > actual 2>&1 &&
+        test_debug "echo -n expected: " &&
+        test_debug "cat expected" &&
+        test_debug "echo -n actual: " &&
+        test_debug "cat actual" &&
+        test_cmp expected actual
+#        rm -f expected actual
+'
+
+# 23
+test_expect_success 'check if --message works for split+rejoin' '
+        spl1=''"$(git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --message "Split & rejoin" --rejoin)"'' &&
+        git branch spl1 "$spl1" &&
+        check_equal ''"$(last_commit_message)"'' "Split & rejoin" &&
+        undo
+'
+
+# 24
+test_expect_success 'check split with --branch' '
+        spl1=$(git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --message "Split & rejoin" --rejoin) &&
+        undo &&
+        git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --branch splitbr1 &&
+        check_equal ''"$(git rev-parse splitbr1)"'' "$spl1"
+'
+
+# 25
+test_expect_success 'check split with --branch for an existing branch' '
+        spl1=''"$(git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --message "Split & rejoin" --rejoin)"'' &&
+        undo &&
+        git branch splitbr2 sub1 &&
+        git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --branch splitbr2 &&
+        check_equal ''"$(git rev-parse splitbr2)"'' "$spl1"
+'
+
+# 26
+test_expect_success 'check split with --branch for an incompatible branch' '
+        test_must_fail git subtree split --prefix subdir --onto FETCH_HEAD --branch subdir
+'
+
+
+# 27
+test_expect_success 'check split+rejoin' '
+        spl1=''"$(git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --message "Split & rejoin" --rejoin)"'' &&
+        undo &&
+        git subtree split --annotate='"'*'"' --prefix subdir --onto FETCH_HEAD --rejoin &&
+        check_equal ''"$(last_commit_message)"'' "Split '"'"'subdir/'"'"' into commit '"'"'"$spl1"'"'"'"
+'
+
+# 28
+test_expect_success 'add main-sub8' '
+        create subdir/main-sub8 &&
+        git commit -m "main-sub8"
+'
+
+# To the subproject!
+cd ./subproj
+
+# 29
+test_expect_success 'merge split into subproj' '
+        git fetch .. spl1 &&
+        git branch spl1 FETCH_HEAD &&
+        git merge FETCH_HEAD
+'
+
+# 30
+test_expect_success 'add sub9' '
+        create sub9 &&
+        git commit -m "sub9"
+'
+
+# Back to mainline
+cd ..
+
+# 31
+test_expect_success 'split for sub8' '
+        split2=''"$(git subtree split --annotate='"'*'"' --prefix subdir/ --rejoin)"''
+        git branch split2 "$split2"
+'
+
+# 32
+test_expect_success 'add main-sub10' '
+        create subdir/main-sub10 &&
+        git commit -m "main-sub10"
+'
+
+# 33
+test_expect_success 'split for sub10' '
+        spl3=''"$(git subtree split --annotate='"'*'"' --prefix subdir --rejoin)"'' &&
+        git branch spl3 "$spl3"
+'
+
+# To the subproject!
+cd ./subproj
+
+# 34
+test_expect_success 'merge split into subproj' '
+        git fetch .. spl3 &&
+        git branch spl3 FETCH_HEAD &&
+        git merge FETCH_HEAD &&
+        git branch subproj-merge-spl3
+'
+
+chkm="main4 main6"
+chkms="main-sub10 main-sub5 main-sub7 main-sub8"
+chkms_sub=$(echo $chkms | multiline | sed 's,^,subdir/,' | fixnl)
+chks="sub1 sub2 sub3 sub9"
+chks_sub=$(echo $chks | multiline | sed 's,^,subdir/,' | fixnl)
+
+# 35
+test_expect_success 'make sure exactly the right set of files ends up in the subproj' '
+        subfiles=''"$(git ls-files | fixnl)"'' &&
+        check_equal "$subfiles" "$chkms $chks"
+'
+
+# 36
+test_expect_success 'make sure the subproj history *only* contains commits that affect the subdir' '
+        allchanges=''"$(git log --name-only --pretty=format:'"''"' | sort | fixnl)"'' &&
+        check_equal "$allchanges" "$chkms $chks"
+'
+
+# Back to mainline
+cd ..
+
+# 37
+test_expect_success 'pull from subproj' '
+        git fetch ./subproj subproj-merge-spl3 &&
+        git branch subproj-merge-spl3 FETCH_HEAD &&
+        git subtree pull --prefix=subdir ./subproj subproj-merge-spl3
+'
+
+# 38
+test_expect_success 'make sure exactly the right set of files ends up in the mainline' '
+        mainfiles=''"$(git ls-files | fixnl)"'' &&
+        check_equal "$mainfiles" "$chkm $chkms_sub $chks_sub"
+'
+
+# 39
+test_expect_success 'make sure each filename changed exactly once in the entire history' '
+        # main-sub?? and /subdir/main-sub?? both change, because those are the
+        # changes that were split into their own history.  And subdir/sub?? never
+        # change, since they were *only* changed in the subtree branch.
+        allchanges=''"$(git log --name-only --pretty=format:'"''"' | sort | fixnl)"'' &&
+        check_equal "$allchanges" ''"$(echo $chkms $chkm $chks $chkms_sub | multiline | sort | fixnl)"''
+'
+
+# 40
+test_expect_success 'make sure the --rejoin commits never make it into subproj' '
+        check_equal ''"$(git log --pretty=format:'"'%s'"' HEAD^2 | grep -i split)"'' ""
+'
+
+# 41
+test_expect_success 'make sure no "git subtree" tagged commits make it into subproj' '
+        # They are meaningless to subproj since one side of the merge refers to the mainline
+        check_equal ''"$(git log --pretty=format:'"'%s%n%b'"' HEAD^2 | grep "git-subtree.*:")"'' ""
+'
+
+# prepare second pair of repositories
+mkdir test2
+cd test2
+
+# 42
+test_expect_success 'init main' '
+        test_create_repo main
+'
+
+cd main
+
+# 43
+test_expect_success 'add main1' '
+        create main1 &&
+        git commit -m "main1"
+'
+
+cd ..
+
+# 44
+test_expect_success 'init sub' '
+        test_create_repo sub
+'
+
+cd sub
+
+# 45
+test_expect_success 'add sub2' '
+        create sub2 &&
+        git commit -m "sub2"
+'
+
+cd ../main
+
+# check if split can find proper base without --onto
+
+# 46
+test_expect_success 'add sub as subdir in main' '
+        git fetch ../sub master &&
+        git branch sub2 FETCH_HEAD &&
+        git subtree add --prefix subdir sub2
+'
+
+cd ../sub
+
+# 47
+test_expect_success 'add sub3' '
+        create sub3 &&
+        git commit -m "sub3"
+'
+
+cd ../main
+
+# 48
+test_expect_success 'merge from sub' '
+        git fetch ../sub master &&
+        git branch sub3 FETCH_HEAD &&
+        git subtree merge --prefix subdir sub3
+'
+
+# 49
+test_expect_success 'add main-sub4' '
+        create subdir/main-sub4 &&
+        git commit -m "main-sub4"
+'
+
+# 50
+test_expect_success 'split for main-sub4 without --onto' '
+        git subtree split --prefix subdir --branch mainsub4
+'
+
+# at this point, the new commit parent should be sub3 if it is not,
+# something went wrong (the "newparent" of "master~" commit should
+# have been sub3, but it was not, because its cache was not set to
+# itself)
+
+# 51
+test_expect_success 'check that the commit parent is sub3' '
+        check_equal ''"$(git log --pretty=format:%P -1 mainsub4)"'' ''"$(git rev-parse sub3)"''
+'
+
+# 52
+test_expect_success 'add main-sub5' '
+        mkdir subdir2 &&
+        create subdir2/main-sub5 &&
+        git commit -m "main-sub5"
+'
+
+# 53
+test_expect_success 'split for main-sub5 without --onto' '
+        # also test that we still can split out an entirely new subtree
+        # if the parent of the first commit in the tree is not empty,
+        # then the new subtree has accidently been attached to something
+        git subtree split --prefix subdir2 --branch mainsub5 &&
+        check_equal ''"$(git log --pretty=format:%P -1 mainsub5)"'' ""
+'
+
+# make sure no patch changes more than one file.  The original set of commits
+# changed only one file each.  A multi-file change would imply that we pruned
+# commits too aggressively.
+joincommits()
+{
+	commit=
+	all=
+	while read x y; do
+		#echo "{$x}" >&2
+		if [ -z "$x" ]; then
+			continue
+		elif [ "$x" = "commit:" ]; then
+			if [ -n "$commit" ]; then
+				echo "$commit $all"
+				all=
+			fi
+			commit="$y"
+		else
+			all="$all $y"
+		fi
+	done
+	echo "$commit $all"
+}
+
+# 54
+test_expect_success 'verify one file change per commit' '
+        x= &&
+        list=''"$(git log --pretty=format:'"'commit: %H'"' | joincommits)"'' &&
+#        test_debug "echo HERE" &&
+#        test_debug "echo ''"$list"''" &&
+        (git log --pretty=format:'"'commit: %H'"' | joincommits |
+        (       while read commit a b; do
+		        test_debug "echo Verifying commit "''"$commit"''
+		        test_debug "echo a: "''"$a"''
+		        test_debug "echo b: "''"$b"''
+		        check_equal "$b" ""
+		        x=1
+	        done
+	        check_equal "$x" 1
+        ))
+'
+
+test_done
diff --git a/contrib/subtree/todo b/contrib/subtree/todo
new file mode 100644
index 0000000000..7e44b0024f
--- /dev/null
+++ b/contrib/subtree/todo
@@ -0,0 +1,50 @@
+
+	delete tempdir
+
+	'git subtree rejoin' option to do the same as --rejoin, eg. after a
+	  rebase
+
+	--prefix doesn't force the subtree correctly in merge/pull:
+	"-s subtree" should be given an explicit subtree option?
+		There doesn't seem to be a way to do this.  We'd have to
+		patch git-merge-subtree.  Ugh.
+		(but we could avoid this problem by generating squashes with
+		exactly the right subtree structure, rather than using
+		subtree merge...)
+
+	add a 'push' subcommand to parallel 'pull'
+	
+	add a 'log' subcommand to see what's new in a subtree?
+
+	add to-submodule and from-submodule commands
+
+	automated tests for --squash stuff
+
+	"add" command non-obviously requires a commitid; would be easier if
+		it had a "pull" sort of mode instead
+
+	"pull" and "merge" commands should fail if you've never merged
+		that --prefix before
+		
+	docs should provide an example of "add"
+	
+	note that the initial split doesn't *have* to have a commitid
+		specified... that's just an optimization
+
+	if you try to add (or maybe merge?) with an invalid commitid, you
+		get a misleading "prefix must end with /" message from
+		one of the other git tools that git-subtree calls.  Should
+		detect this situation and print the *real* problem.
+	
+	"pull --squash" should do fetch-synthesize-merge, but instead just
+		does "pull" directly, which doesn't work at all.
+
+	make a 'force-update' that does what 'add' does even if the subtree
+		already exists.  That way we can help people who imported
+		subtrees "incorrectly" (eg. by just copying in the files) in
+		the past.
+
+	guess --prefix automatically if possible based on pwd
+
+	make a 'git subtree grafts' that automatically expands --squash'd
+		commits so you can see the full history if you want it.