github conflicting PRs

COMPAT.png

CONFLICT.png

gistfile1.txt

Assuming you have pull requests as part of your github remote:

    [remote "origin"]
      url = https://github.com/bitcoin/bitcoin.git
      fetch = +refs/heads/*:refs/remotes/origin/*
      fetch = +refs/pull/*/head:refs/pull/origin/*

You can do a plausible looking check for conflicts between pull requests 1, 2, 3, 4 and 5 with:

    tsts="1 2 3 4 5"
    for xa in $tsts; do
        a=pull/origin/$xa
        if (git reset --hard origin/master && git merge $a -m "merge $a to master") >/dev/null; then
            for xb in $tsts; do
                git reset --hard $a >/dev/null
                if [ "$xa" -ge "$xb" ]; then continue; fi
                b=pull/origin/$xb
                if (git format-patch $(git merge-base $a $b)..$b --stdout | git apply --check -) > APPLY_${xa}_${xb} 2>&1; then
                    echo "no conflict between $xa $xb"
                else
                    echo "merge conflict $xa $xb ?"
                fi
            done
        else
            echo "conflict with $a and master"
        fi
    done > CONFLICT
    
format-patch and apply --check don't touch the working tree, so it's not too inefficient.

Graphing:

    (echo "graph compat {"; cat CONFLICT | sed -n 's/merge conflict \([0-9]*\) \([0-9]*\) .$/  \1 -- \2/p'; echo }) | dot -Tpng > CONFLICT.png

    (echo "graph compat {"; cat CONFLICT | sed -n 's/no conflict between \([0-9]*\) \([0-9]*\)/  \1 -- \2/p'; echo }) | dot -Tpng > COMPAT.png