#!/bin/bash

# shows the commit that "landed" a branch on HEAD
#
#  git landed $commit-on-branch [ $head-to-land-on ] [ git-log options ]

declare -a revs
declare -a flags

for p in "$@"; do
    if [[ $p =~ ^- ]]; then
        flags+=( "$p" )
    else
        revs+=( "$p" )
    fi
done

there="${revs[0]:?need a commitish}"
here="${revs[1]:-HEAD}"

git log "$here" ^"$there" --ancestry-path --merges --reverse -z "${flags[@]}" \
    | head -z -n 1