git-subtree.sh

#!/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_$command" "$@"