update-4x-branch.sh

#!/bin/bash
#
# Create a PR to update the 4.x branch to match the state of "main" for the
# just-tagged release. The 4.x branch needs to be updated for the current docs
# build.
#

if [ "$TRACE" != "" ]; then
    export PS4='${BASH_SOURCE}:${LINENO}: ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
    set -o xtrace
fi
set -o errexit
set -o pipefail

function fatal {
    echo "$(basename $0): error: $*"
    exit 1
}

TOP=$(cd $(dirname $0)/../ >/dev/null; pwd)
WRKDIR=${TOP}/build/update-4x-branch

echo "# Creating working git clone in: ${WRKDIR}/apm-agent-nodejs"
rm -rf $WRKDIR
mkdir -p $WRKDIR
cd $WRKDIR
git clone git@github.com:elastic/apm-agent-nodejs.git
cd apm-agent-nodejs

TARGTAG=$(git tag --points-at HEAD)
if [[ ! ("$TARGTAG" =~ ^v[0-9]+\.[0-9]+\.[0-9]$) ]]; then
    fatal "the tag on HEAD, '${TARGTAG}', does not look like a release tag"
fi
# echo "TARGTAG=$TARGTAG"

readonly NUM_COMMITS_SANITY_GUARD=200
LASTTAG=$(
    git log --pretty=format:%h -$NUM_COMMITS_SANITY_GUARD | tail -n +2 | while read sha; do
        possible=$(git tag --points-at $sha)
        if [[ "$possible" =~ ^v[0-9]+\.[0-9]+\.[0-9]$ ]]; then
            echo $possible
            break
        fi
    done
)
if [[ -z "$LASTTAG" ]]; then
    fatal "could not find previous release tag in last $NUM_COMMITS_SANITY_GUARD commits"
fi
# echo "LASTTAG=$LASTTAG"


# Merging generally fails, IME. Let's attempt to cherry-pick each commit.
# - That 'awk' command is to reverse the lines of commit shas.
#   `tac` works on Linux, `tail -r` works on BSD/macOS.
#   https://stackoverflow.com/a/744093/14444044
echo
echo "# Creating PR to update 4.x branch with commits from $LASTTAG to $TARGTAG."
FEATBRANCH=update-4x-branch-$(date +%Y%m%d)
git checkout 4.x
git checkout -b "$FEATBRANCH"
git log --pretty=format:"%h" $LASTTAG...$TARGTAG \
    | awk '{a[i++]=$0} END {for (j=i-1; j>=0;) print a[j--] }' \
    | while read sha; do
        echo "$ git cherry-pick $sha"
        git cherry-pick $sha
    done

RELEASE_PR=$(git log --pretty=format:"%s" -1 $TARGTAG | sed -E 's/^.* \(\#([0-9]+)\)$/\1/')
echo
echo "# You can create a PR now with:"
echo "    cd $WRKDIR/apm-agent-nodejs"
echo "    gh pr create -w -B 4.x -t 'docs: update 4.x branch for $TARGTAG release' --body 'Refs: #$RELEASE_PR (release PR)'"