#!/bin/sh
# scripts/bite --- prove a fix's tests BITE: run them against an older
# version of ONE file and succeed only if they FAIL there.
#
#   scripts/bite <ref> <path> [cargo-test-args...]
#
# Example (the PR #111 round-1 shape):
#   scripts/bite HEAD~1 builtin/runtime/editops.lua \
#       --test editops_acceptance -- capitalize trim_on_save_unexpected
#
# Exit status: 0 when the named tests fail against <ref>'s version of
# <path> (the fix bites), 1 when they still pass (vacuous), 2 on
# usage/setup errors. The working-tree file is restored on every exit
# path, including interrupts.
#
# Caveat: a COMPILE error of the old tree also counts as "fails" —
# correct, but weaker evidence than a clean assertion failure; eyeball
# the output when the swapped file is Rust rather than Lua.
#
# Why this exists: bite-verification is step 4 of the working method,
# and the obvious shortcut — git stash — is a trap here. The stash
# namespace is REPO-GLOBAL: shared across every worktree and with
# humans, so a scripted push/pop can collide with (or pop!) someone
# else's stashed work. This helper never touches git state beyond a
# read-only `git show`.

set -eu

if [ "$#" -lt 2 ]; then
    echo "usage: scripts/bite <ref> <path> [cargo-test-args...]" >&2
    exit 2
fi

ref=$1
path=$2
shift 2

if [ ! -f "$path" ]; then
    echo "bite: no such file: $path" >&2
    exit 2
fi

saved=$(mktemp "${TMPDIR:-/tmp}/bite.XXXXXX")
cp -- "$path" "$saved"
restore() {
    cp -- "$saved" "$path"
    rm -f -- "$saved"
}
trap restore EXIT INT TERM

# The `./` prefix makes the pathspec cwd-relative for git-show, so the
# script works from any directory inside the repo.
git show "$ref:./$path" > "$path"

if cargo test "$@"; then
    echo "bite: VACUOUS --- tests still pass against $ref:$path" >&2
    exit 1
fi

echo "bite: OK --- tests fail against $ref:$path (the fix bites)"