#!/usr/bin/env bash
# Records this run's HEAD as the watermark restore-mtimes.sh reads back on
# this cache directory's NEXT run.
#
# Usage: record-watermark.sh <target-dir> <watermark-file-name>
#
# Run only after the build has succeeded: a failed run leaves the watermark at
# the last GREEN build, which is the conservative direction (over-invalidates,
# never under-invalidates). See restore-mtimes.sh's header for what the
# watermark is for.
#
# Written with write-then-rename so this directory's next run can never
# observe a truncated, half-written watermark.
set -euo pipefail
DIR="${1:?usage: record-watermark.sh <target-dir> <watermark-file-name>}"
NAME="${2:?}"
mkdir -p "$DIR"
git rev-parse HEAD > "$DIR/${NAME}.tmp"
mv -f "$DIR/${NAME}.tmp" "$DIR/${NAME}"
echo "watermark: $(cat "$DIR/${NAME}") recorded in ${DIR}/${NAME}"