#!/bin/sh
# scripts/bite --- prove a fix's tests BITE: run them against the
# working tree (they must PASS), then against an older version of ONE
# file (they must FAIL).
#
#   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 pass now and fail against
# <ref>'s version of <path> (the fix bites), 1 when they still pass
# there (vacuous), 2 on usage/setup errors, 3 when the POSITIVE
# CONTROL fails. The working-tree file is restored on every exit path,
# including interrupts.
#
# THE POSITIVE CONTROL, and why it is not optional. Before this
# existed the script ran only the swapped tree, so it could not
# distinguish "my fix is load-bearing" from "my test is broken": a
# typo, an unrelated compile break, or a filter that matches nothing
# all made the swapped run fail, and a failing swapped run was the
# only thing it checked. It printed `bite: OK` and certified nothing.
# So the control asserts two things, because passing alone is not
# enough — `cargo test` with a filter matching zero tests exits 0, and
# then a compile error in the old tree would still read as OK:
#
#   * the named tests PASS against the working tree, and
#   * at least one test actually RAN.
#
# COMPILE errors of the old tree still count as "fails", and that is
# correct but weaker than a clean assertion failure --- the swapped
# file may simply not build against the current tree. The script now
# says which kind it saw instead of leaving it to be eyeballed. Prefer
# an assertion failure; treat a compile failure as a prompt to narrow
# the swap to a file that compiles both ways.
#
# That classification reads libtest's own `test result:` summary and
# deliberately does NOT grep for compiler text. A test may PRINT
# compiler output on failure --- `compile_mode_acceptance` has a
# fixture that emits `error[E0308]: mismatched types` at column 0, and
# the compile-mode and editops suites are this script's primary
# consumers --- so a `^error[E...]` grep would stamp "weaker evidence"
# on exactly the strong result it was meant to identify. `test result:`
# is emitted whenever the harness ran, is absent when the swapped file
# did not build, and stays uncolored when piped.
#
# 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`, and it restores the working file from a
# mktemp copy --- NOT from git, so uncommitted work in <path> is
# preserved.

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

# Both cargo runs are CAPTURED rather than streamed, because their
# output is parsed (passed-counts for the control, `test result:` for
# the classification). A long acceptance suite therefore prints
# nothing until it finishes --- that is the trade, not a bug. Do not
# "fix" it back to streaming without giving the parser another source.
#
# Colour is pinned off on both runs: `--color always` in the
# passed-through args would otherwise wrap the summary lines in escape
# codes, and every anchored match here would silently stop matching.
export CARGO_TERM_COLOR=never

# Sum the `N passed` figures across every `test result:` line, so a
# multi-target invocation is counted correctly rather than only its
# last binary.
count_passed() {
    sed -n 's/^test result: ok\. \([0-9][0-9]*\) passed.*/\1/p' \
        | awk '{ total += $1 } END { print total + 0 }'
}

# --- Positive control: the tests must pass, and must exist, NOW. ---
echo "bite: positive control --- running against the working tree" >&2
control_status=0
control_out=$(cargo test "$@" 2>&1) || control_status=$?
printf '%s\n' "$control_out"

if [ "$control_status" -ne 0 ]; then
    echo "bite: NO CONTROL --- tests do not pass against the working tree." >&2
    echo "bite: fix the tests first; a failure here makes the swapped run meaningless." >&2
    exit 3
fi

control_ran=$(printf '%s\n' "$control_out" | count_passed)
if [ "$control_ran" -eq 0 ]; then
    echo "bite: NO CONTROL --- the filter matched no tests (0 passed)." >&2
    echo "bite: check the test names; an empty filter passes everywhere and proves nothing." >&2
    exit 3
fi
echo "bite: control OK --- $control_ran test(s) pass against the working tree" >&2

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"

echo "bite: swapping in $ref:$path" >&2
swapped_status=0
swapped_out=$(cargo test "$@" 2>&1) || swapped_status=$?
printf '%s\n' "$swapped_out"

if [ "$swapped_status" -eq 0 ]; then
    echo "bite: VACUOUS --- tests still pass against $ref:$path" >&2
    exit 1
fi

# Distinguish the ways the swapped run can fail. An assertion failure
# is the evidence we want; a build failure only says the old file does
# not compile here, and the tests may never have run at all.
#
# Classified from libtest's summary line, NOT from compiler text --- a
# failing test can print `error[E0308]: ...` at column 0 itself (see
# the header). `test result: FAILED` means the harness ran and tests
# failed; no `test result:` line at all means nothing ran.
if printf '%s\n' "$swapped_out" | grep -q '^test result: FAILED'; then
    echo "bite: OK (assertion) --- tests fail against $ref:$path (the fix bites)"
elif printf '%s\n' "$swapped_out" | grep -q '^test result:'; then
    # Some target ran to completion without a failure, yet cargo still
    # exited non-zero --- typically a *different* target in the same
    # invocation failed to build. Neither clean result applies.
    echo "bite: OK (MIXED) --- some tests ran and none failed, but the run still failed." >&2
    echo "bite: narrow the invocation to one target before trusting this." >&2
else
    echo "bite: OK (COMPILE) --- $ref:$path does not build against the current tree." >&2
    echo "bite: weaker evidence than an assertion failure --- the tests may never have run." >&2
fi