git-release2

#!/bin/bash

SUBDIRECTORY_OK=Yes
OPTIONS_KEEPDASHDASH=
OPTIONS_SPEC="\
release2 --old <old> --new <new> --base <base> <project1> <project2>...
release2 --continue

release2 recreates an integration branch, making it easy to remove branches
which proved unstable. Merge conflict resolutions are learned from the
existing branch and used when creating the new branch.
--
o,old=     name of old branch to recreate
n,new=     name of new branch to create
b,base=    commit to base new branch on
continue   resume merges
train      train rerere first
"
. $(git --exec-path)/git-sh-setup
require_work_tree_exists
cd_to_toplevel

ensure_branch() {
    branch="$1"
    if ! git rev-parse -q --verify "refs/heads/$branch" >/dev/null ; then
        if ! git rev-parse -q --verify "refs/remotes/origin/$branch" >/dev/null ; then
            echo >&2 "Unknown branch: $branch"
            exit 1
        fi
        git branch --track "$branch" "origin/$branch"
    fi
}

old=
new=
base=
continue=
train=

while test $# != 0 ; do
    case "$1" in
        -b|--base)
            test 2 -le "$#" || usage
            base="$2"
            shift
            ;;
        -n|--new)
            test 2 -le "$#" || usage
            new="$2"
            shift
            ;;
        -o|--old)
            test 2 -le "$#" || usage
            old="$2"
            shift
            ;;
        --continue)
            continue=1
            ;;
        --train)
            train=1
            ;;
        --)
            shift; break ;;
        *)
            echo "unknown opt $1"
            usage ;;
    esac
    shift
done

# Make sure index and tree are clean
git diff-index --quiet HEAD || {
    echo >&2 "You have uncommitted work. Exiting."
    exit 1
}

if [ -n "$continue" ] ; then
    new="$(cat $GIT_DIR/RELEASE2_NEW)"
    set -- $(cat $GIT_DIR/RELEASE2_REMAINING)
fi

test $# -eq 0 && usage

# Check the branches
for prj in "$old" "$@" ; do
    ensure_branch "$prj"
done

if [ -n "$continue" ] ; then
    new="$(cat $GIT_DIR/RELEASE2_NEW)"
    if [ "$(git symbolic-ref HEAD)" != "$new" ] ; then
        echo >&2 "You are not on the branch you started on ($new)."
    fi
else
    # Make sure new branch does not exist
    ( git rev-parse -q --verify "refs/heads/$new" >/dev/null || \
        git rev-parse -q --verify "refs/remotes/origin/$new" >/dev/null ) && {
        echo >&2 "branch $new already exists"
        exit 1
    }

    # Create new branch and check it out
    git checkout -b "$new" "$base"

    if [ -n "$train" ] ; then
        # Record existing resolutions
        git rerere-train "$old" "^$base"
    fi
fi

# Merge each one
while test $# != 0 ; do
    git merge "$1" || {
        echo $* > $GIT_DIR/RELEASE2_NEW
        echo $* > $GIT_DIR/RELEASE2_REMAINING
        echo >&2 "Re-run with --continue the conflicts are fixed."
        exit 1
    }
    shift
done