An extension for git to git-merge a single specified file from another revision

git-merge-pick

#!/usr/bin/env bash

usage () {
    cat << EOH
    git merge-pick [flags] <tree-ish> path/to/file

    being <tree-ish> a commit-like object (a commit sha1,
    a branch name or a tag).

    [flags]
    -s, --strategy: merge strategy (see man git-merge)
EOH
}

main() {
    GITMP_GATHERER=()
    while [[ $# -gt 0 ]]; do
        key=$1
        case $key in
            -h|--help)
                usage
                exit 0
                ;;
            -v|--verbose)
                GITMP_DEBUG="true"
                shift
                ;;
            *)
                if [[ $GITMP_DEBUG = "true" ]]; then
                    print_debug "level_1: $1"
                fi
                GITMP_GATHERER+=($1)
                shift
                ;;
        esac
    done

    print_debug "level_2: ${GITMP_GATHERER[@]}"

    merge_pick_wrapper ${GITMP_GATHERER[@]}
}

merge_pick_wrapper() {
    if [[ $# -lt 2 ]]; then
        usage
        exit 2
    fi

    GITMP_FLAGS=()
    while [[ $# -gt 0 ]]; do
    key="$1"
        case $1 in

            -*)
                interpret_flag $1 $2
                shift
                shift
                ;;
            *)
                parse_tree_info $1
                parse_file_info $1 $2
                shift
                shift
                ;;
        esac
    done

    print_debug "GITMP_DEBUG=$GITMP_DEBUG"
    print_debug "GITMP_STRATEGY=$GITMP_STRATEGY"
    print_debug "GITMP_TARGET_REV=$GITMP_TARGET_REV"
    print_debug "GITMP_TARGET_FILE=$GITMP_TARGET_FILE"

    # merge_pick $GITMP_FLAGS $GITMP_TARGET_REV $GITMP_TARGET_FILE
    merge_pick
}

print_debug() {
    if [[ $GITMP_DEBUG = "true" ]]; then
        echo "[DEBUG] $@"
    fi
}

interpret_flag() {
    case $1 in
        -h|--help)
            usage
            exit 0
            ;;
        -s|--strategy)
            shift
            GITMP_STRATEGY=$1
            GITMP_FLAGS+=("-s $GITMP_STRATEGY")
            shift
            ;;
        *)
            continue
            ;;
    esac
}

parse_tree_info() {
    GITMP_CURRENT_REV=$(git rev-parse HEAD)
    if [ ! $(git rev-parse --quiet --verify $1) ]; then
        echo "$1 is not a valid reference"
        exit 3
    fi
    GITMP_ORIG_REV=$(git symbolic-ref --short HEAD)
    GITMP_TARGET_REV=$(git rev-parse $1)
}

parse_file_info() {
    if [[ ! -f $2 ]]; then
        if [[ $(comm -23 <(echo $2) <(git diff --names-only --diff-filter=AM $1)) != "" ]]; then
            print_debug "GITMP_TARGET_FILE=$2"
            print_debug "GITMP_TARGET_REV=$1"
            print_debug "Diff from target tree point"
            print_debug "---------------------------"
            print_debug ""
            print_debug "$(git diff --names-only --diff-filter=AM HEAD $1)"
            exit 4
        fi
    fi
    GITMP_TARGET_FILE=$2
}

merge_pick() {
    GITMP_TMP_BRANCH="git-merge-pick-$RANDOM"
    git stash push
    git checkout -b $GITMP_TMP_BRANCH
    git checkout $GITMP_TARGET_REV $GITMP_TARGET_FILE
    git add $GITMP_TARGET_FILE
    git commit -m "Merge $GITMP_TARGET_FILE from \
                    $GITMP_TARGET_REV into $GITMP_ORIG_REV"
    git checkout $GITMP_ORIG_REV
    git merge -m "$GITMP_TARGET_FILE merged from $GITMP_TARGET_REV" \
        ${GITMP_FLAGS[@]} $GITMP_TMP_BRANCH
    git branch -D $GITMP_TMP_BRANCH
    git stash pop
}

main $@