gitdan-actions/scripts/seed-target-dir-selftest.sh

#!/usr/bin/env bash
# Regression test for seed-target-dir.sh: which source a run seeds from, and
# what happens when two jobs sharing one cache key seed at the same time.
#
# Runs the ACTUAL script against a real scratch cache directory with fake
# target trees standing in for cargo output — no compiler needed, so this is
# the fast half of the suite. hardlink-clone-selftest.sh covers the parts that
# need a real build.
#
# What each scenario demonstrates:
#
#   1. BASE SNAPSHOT PREFERRED — a PR whose base has published a snapshot
#      seeds from it, and the seeded directory really is a hardlink clone
#      (shared inodes), not a copy.
#   2. OWN DIR WINS — a second run of the same ref reuses what is already
#      there and does not re-seed over its own work.
#   3. OWN SNAPSHOT AS SELF-RESTORE — a publisher whose live target dir was
#      evicted restores from the snapshot it last published, instead of
#      rebuilding cold.
#   4. FALLBACK DIR — with no snapshot at all, an explicitly configured
#      fallback (a pre-existing flat cache, during a migration) is used.
#   5. COLD — with nothing available, the directory is created empty rather
#      than the script failing.
#   6. LOCK FILES STRIPPED — Cargo's in-place-flock'd lock files never
#      survive a clone, because a shared lock inode would make two branches
#      contend on one mutex.
#   7. CONCURRENT SEED IS ATOMIC — two seeds racing on one cache key: the
#      loser discards its staging copy and uses the winner's directory, and
#      at no point is a partially-populated directory visible under the final
#      name. This is the property that replaces "the runner only has one job
#      slot" with an actual guarantee.
set -euo pipefail
script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
. "$script_dir/cache-lib.sh"

scratch=$(mktemp -d)
trap 'rm -rf "$scratch"' EXIT
root="$scratch/cache"
mkdir -p "$root"
pass_count=0

fail() { echo "ASSERTION FAILED: $*" >&2; exit 1; }
ok() { pass_count=$((pass_count + 1)); echo "PASS: $*"; }
assert_file() { [ -e "$1" ] || fail "expected $1 to exist ($2)"; ok "$2"; }
assert_absent() { [ -e "$1" ] && fail "expected $1 to be gone ($2)"; ok "$2"; }
assert_content() { [ "$(cat "$1")" = "$2" ] || fail "expected '$2' in $1, got '$(cat "$1")' ($3)"; ok "$3"; }

# A plausible target tree: a big shared artifact, a mutable fingerprint, a
# build-script output, and a lock file.
make_tree() {
  local d="$1" marker="$2"
  mkdir -p "$d/debug/deps" "$d/debug/.fingerprint/x" "$d/debug/build/x/out"
  echo "$marker" > "$d/debug/deps/libx.rlib"
  echo "$marker" > "$d/debug/.fingerprint/x/dep-lib-x"
  echo "$marker" > "$d/debug/build/x/out/gen.txt"
  : > "$d/debug/.cargo-lock"
}

seed() { bash "$script_dir/seed-target-dir.sh" "$@" > "$scratch/log" 2>&1 || { cat "$scratch/log"; fail "seed-target-dir.sh exited non-zero"; }; }

BASE_KEY=$(cache_key dev)
OWN_KEY=$(cache_key feat/thing)

echo "=== 1: base snapshot preferred, and cloned by hardlink ==="
make_tree "$root/snapshot-$BASE_KEY" base-content
seed "$OWN_KEY" "$BASE_KEY" "$root" job1
own="$root/target-$OWN_KEY"
assert_content "$own/debug/deps/libx.rlib" base-content "seeded from the base snapshot"
[ "$(stat -c '%i' "$own/debug/deps/libx.rlib")" = "$(stat -c '%i' "$root/snapshot-$BASE_KEY/debug/deps/libx.rlib")" ] \
  || fail "artifact was copied, not hardlinked"
ok "artifact shares an inode with the snapshot (hardlink clone, not a copy)"
[ "$(stat -c '%i' "$own/debug/.fingerprint/x/dep-lib-x")" != "$(stat -c '%i' "$root/snapshot-$BASE_KEY/debug/.fingerprint/x/dep-lib-x")" ] \
  || fail "fingerprint still shares an inode with the snapshot"
ok "fingerprint is privately owned (unshare_mutable_paths ran)"

echo
echo "=== 6: Cargo lock files never survive a clone ==="
assert_absent "$own/debug/.cargo-lock" "cloned .cargo-lock removed"

echo
echo "=== 2: an existing own dir is reused, never re-seeded over ==="
echo own-work > "$own/debug/deps/libx.rlib"
seed "$OWN_KEY" "$BASE_KEY" "$root" job1
assert_content "$own/debug/deps/libx.rlib" own-work "own directory reused as-is"
grep -q 'reusing this ref' "$scratch/log" || fail "expected the reuse path in the log"
ok "reuse is reported in the log"

echo
echo "=== 3: a publisher restores from its own snapshot after eviction ==="
make_tree "$root/snapshot-$BASE_KEY" published-dev
seed "$BASE_KEY" "" "$root" job1
assert_content "$root/target-$BASE_KEY/debug/deps/libx.rlib" published-dev "publisher self-restored from its own snapshot"

echo
echo "=== 4: explicit fallback dir when no snapshot exists ==="
OTHER=$(cache_key feat/other)
make_tree "$scratch/legacy-flat" legacy
seed "$OTHER" "$(cache_key nosuch)" "$root" job1 "$scratch/legacy-flat"
assert_content "$root/target-$OTHER/debug/deps/libx.rlib" legacy "seeded from the fallback dir"

echo
echo "=== 5: cold start when nothing is available ==="
COLD=$(cache_key feat/cold)
seed "$COLD" "$(cache_key nosuch)" "$root" job1
[ -d "$root/target-$COLD" ] || fail "cold start did not create the directory"
[ -z "$(ls -A "$root/target-$COLD")" ] || fail "cold start directory is not empty"
ok "cold start creates an empty directory rather than failing"

echo
echo "=== 7: two jobs racing on one cache key ==="
RACE=$(cache_key feat/race)
make_tree "$root/snapshot-$BASE_KEY" race-source
# Both jobs seed concurrently from the same snapshot into the same key. Each
# stages under its own tag, so the only interaction is the final rename.
( bash "$script_dir/seed-target-dir.sh" "$RACE" "$BASE_KEY" "$root" jobA > "$scratch/logA" 2>&1 ) &
( bash "$script_dir/seed-target-dir.sh" "$RACE" "$BASE_KEY" "$root" jobB > "$scratch/logB" 2>&1 ) &
wait
race_dir="$root/target-$RACE"
assert_content "$race_dir/debug/deps/libx.rlib" race-source "the surviving directory is complete"
[ -z "$(find "$root" -maxdepth 1 -name '.stage-*' -print -quit)" ] || fail "a staging directory was left behind"
ok "no staging directory survived the race"
# Exactly one job may claim it seeded; the other must report either the
# concurrent-peer path or a plain reuse (if it started after the winner
# finished). Neither may report a cold start.
if grep -q 'starts cold' "$scratch/logA" "$scratch/logB"; then
  cat "$scratch/logA" "$scratch/logB"; fail "a racing job reported a cold start"
fi
ok "neither racing job fell through to a cold start"

echo
echo "seed-target-dir-selftest: ${pass_count} assertions passed"