A shell script for back-porting Doctrine DBAL pull requests from master to older branches

backport.sh

#!/usr/bin/env bash

set -eu

if [ $# -ne 2 ]; then
    echo "Usage: `basename $0` <pull> <branch>";
    exit 1;
fi

PULL="$1"
TARGET_BRANCH="$2"
TOPIC_BRANCH="bpo/$TARGET_BRANCH/#$PULL"

git fetch -f upstream "pull/$PULL/head:$TOPIC_BRANCH"
git checkout "$TOPIC_BRANCH"

# https://stackoverflow.com/a/30563070/146187
MERGE_BASE=$(diff -u \
    <(git rev-list --first-parent upstream/master) \
    <(git rev-list --first-parent HEAD) \
    | sed -ne "s/^ //p" \
    | head -1
)

git rebase "$MERGE_BASE" --onto "$TARGET_BRANCH"
git checkout "$TARGET_BRANCH"
git merge "$TOPIC_BRANCH" --no-ff --no-edit
git branch -D "$TOPIC_BRANCH"

The remote pointing to the https://github.com/doctrine/dbal repository is expected to be named upstream.

Example usage: ./backport.sh 3385 2.9.