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#!/bin/sh
#
# git-subtree.sh: split/join git repositories in subdirectories of this one
#
# Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
#
if [ $# -eq 0 ]; then
set -- -h
fi
OPTS_SPEC="\
git subtree add --prefix=<prefix> <commit>
git subtree add --prefix=<prefix> <repository> <ref>
git subtree merge --prefix=<prefix> <commit>
git subtree pull --prefix=<prefix> <repository> <ref>
git subtree push --prefix=<prefix> <repository> <ref>
git subtree split --prefix=<prefix> <commit...>
--
h,help show the help
q quiet
d show debug messages
P,prefix= the name of the subdir to split out
m,message= use the given message as the commit message for the merge commit
options for 'split'
annotate= add a prefix to commit message of new commits
b,branch= create a new branch from the split subtree
ignore-joins ignore prior --rejoin commits
onto= try connecting new tree to an existing one
rejoin merge the new branch back into HEAD
options for 'add', 'merge', 'pull' and 'push'
squash merge subtree changes as a single commit
"
eval "$(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=
prefix=

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' "$1" |
(
read GIT_AUTHOR_NAME
read GIT_AUTHOR_EMAIL
read GIT_AUTHOR_DATE
read GIT_COMMITTER_NAME
read GIT_COMMITTER_EMAIL
read GIT_COMMITTER_DATE
export GIT_AUTHOR_NAME \
GIT_AUTHOR_EMAIL \
GIT_AUTHOR_DATE \
GIT_COMMITTER_NAME \
GIT_COMMITTER_EMAIL \
GIT_COMMITTER_DATE
(printf "%s" "$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
}

ensure_valid_ref_format()
{
git check-ref-format "refs/heads/$1" ||
die "'$1' does not look like a ref"
}

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.
ensure_valid_ref_format "$2"

"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()
{
if [ $# -ne 2 ]; then
die "You must provide <repository> <ref>"
fi
ensure_clean
ensure_valid_ref_format "$2"
git fetch "$@" || exit $?
revs=FETCH_HEAD
set -- $revs
cmd_merge "$@"
}

cmd_push()
{
if [ $# -ne 2 ]; then
die "You must provide <repository> <ref>"
fi
ensure_valid_ref_format "$2"
if [ -e "$dir" ]; then
repository=$1
refspec=$2
echo "git push using: " $repository $refspec
localrev=$(git subtree split --prefix="$prefix") || die
git push $repository $localrev:refs/heads/$refspec
else
die "'$dir' must already exist. Try 'git subtree add'."
fi
}

"cmd_$command" "$@"
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