git-upstream-brdiff

#!/bin/sh

# TODO: make it possible to continue this process if one of the cherry-picks
# results in a merge conflict. We just need an optional --continue flag and
# some convention for a tempfile to keep the relevant data.

usage()
{
    cat >&2 <<__EOF__
Usage: $(basename $0) <upstream-branch> <parent-branch> <branch>
__EOF__
    exit ${1-1}
}

log()
{
    echo "$(basename $0): $1" >&2
}

git()
{
    $(which git) $@
    [ $? -ne 0 ] && exit 1
}

[ $# -eq 3 ] || usage

upstream=$1
parent=$2
branch=$3

revlist=$(git cherry $parent $branch | awk '{print $2}' | tail -r)

mrgcommits=$(git log --format=oneline $parent | \
             grep "Merge branch '$branch' into $parent" | \
             awk '{print $1}')

for commit in ${mrgcommits}; do
    parcommit=$(git show --pretty=%P $commit | awk '{print $2}')
    revlist="$parcommit $revlist"
done

currb=$(git branch | awk '$1 == "*" {print $2}')
git checkout $upstream

tmpbranch=$(date "+%Y%m%d")-tmp$$
log "creating temporary branch '$tmpbranch' on branch '$upstream'"
git checkout -b $tmpbranch
trap "git checkout -f ${currb}; git branch -q -D ${tmpbranch}; exit" \
     SIGHUP SIGINT SIGTERM EXIT

for commit in ${revlist}; do
    # XXX there is probably a better way to do this.
    git cherry-pick $commit >/dev/null
done

git diff ${upstream}..HEAD