git difftopic

#!/bin/bash

# Assuming master is the main branch and first argument is topic branch

topicsha=$(git rev-parse "$1")
mergebase=$(git merge-base master "$1")


if [[ $topicsha != $mergebase ]]; then
    # Not merged yet! ez
    git diff master..."$1"
else
    # Oh no, it's already merged. Find merge in log
    # This prints sha parent1sha [ parent2sha ... ]
    mergecommit=$(git log --format='%H %P' |
        awk -vtopicsha="$topicsha" ' $3 == topicsha { print $1; exit }'
    )

    if [[ -n $mergecommit ]]; then
        # ez
        git diff "$mergecommit^1...$mergecommit^2"
    else
        echo oops >&2;
        exit 1
    fi
fi