contrib/subtree/git-subtree.sh - git - Git at Google

 #!/bin/bash
 #
 # git-subtree.sh: split/join git repositories in subdirectories of this one
 #
 # Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
 #
 if [ $# -eq 0 ]; then
     set -- -h
 fi
 OPTS_SPEC="\
 git subtree add   --prefix=<prefix> <commit>
 git subtree add   --prefix=<prefix> <repository> <commit>
 git subtree merge --prefix=<prefix> <commit>
 git subtree pull  --prefix=<prefix> <repository> <refspec...>
 git subtree push  --prefix=<prefix> <repository> <refspec...>
 git subtree split --prefix=<prefix> <commit...>
 --
 h,help        show the help
 q             quiet
 d             show debug messages
 P,prefix=     the name of the subdir to split out
 m,message=    use the given message as the commit message for the merge commit
  options for 'split'
 annotate=     add a prefix to commit message of new commits
 b,branch=     create a new branch from the split subtree
 ignore-joins  ignore prior --rejoin commits
 onto=         try connecting new tree to an existing one
 rejoin        merge the new branch back into HEAD
  options for 'add', 'merge', 'pull' and 'push'
 squash        merge subtree changes as a single commit
 "
 eval "$(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%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
 	    git rev-parse -q --verify "$1^{commit}" >/dev/null ||
 	    die "'$1' does not refer to a commit"

 	    "cmd_add_commit" "$@"
 	elif [ $# -eq 2 ]; then
 	    # Technically we could accept a refspec here but we're
 	    # just going to turn around and add FETCH_HEAD under the
 	    # specified directory.  Allowing a refspec might be
 	    # misleading because we won't do anything with any other
 	    # branches fetched via the refspec.
 	    git rev-parse -q --verify "$2^{commit}" >/dev/null ||
 	    die "'$2' does not refer to a commit"

 	    "cmd_add_repository" "$@"
 	else
 	    say "error: parameters were '$@'"
 	    die "Provide either a commit or a repository and commit."
 	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_$command" "$@"
	#!/bin/bash
	#
	# git-subtree.sh: split/join git repositories in subdirectories of this one
	#
	# Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
	#
	if [ $# -eq 0 ]; then
	set -- -h
	fi
	OPTS_SPEC="\
	git subtree add --prefix=<prefix> <commit>
	git subtree add --prefix=<prefix> <repository> <commit>
	git subtree merge --prefix=<prefix> <commit>
	git subtree pull --prefix=<prefix> <repository> <refspec...>
	git subtree push --prefix=<prefix> <repository> <refspec...>
	git subtree split --prefix=<prefix> <commit...>
	--
	h,help show the help
	q quiet
	d show debug messages
	P,prefix= the name of the subdir to split out
	m,message= use the given message as the commit message for the merge commit
	options for 'split'
	annotate= add a prefix to commit message of new commits
	b,branch= create a new branch from the split subtree
	ignore-joins ignore prior --rejoin commits
	onto= try connecting new tree to an existing one
	rejoin merge the new branch back into HEAD
	options for 'add', 'merge', 'pull' and 'push'
	squash merge subtree changes as a single commit
	"
	eval "$(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%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
	git rev-parse -q --verify "$1^{commit}" >/dev/null \|\|
	die "'$1' does not refer to a commit"

	"cmd_add_commit" "$@"
	elif [ $# -eq 2 ]; then
	# Technically we could accept a refspec here but we're
	# just going to turn around and add FETCH_HEAD under the
	# specified directory. Allowing a refspec might be
	# misleading because we won't do anything with any other
	# branches fetched via the refspec.
	git rev-parse -q --verify "$2^{commit}" >/dev/null \|\|
	die "'$2' does not refer to a commit"

	"cmd_add_repository" "$@"
	else
	say "error: parameters were '$@'"
	die "Provide either a commit or a repository and commit."
	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_$command" "$@"