ersatztv/scripts/tests/test_prepush_unsets_git_env.py

"""`.husky/pre-push` line 11 — `unset GIT_DIR GIT_WORK_TREE GIT_INDEX_FILE` — is load-bearing.

That one line is the fix for a real, silent defect, and ersatztv#785 ranks it third because nothing
pinned it: reordering it after the nested git calls, or dropping it in a tidy-up, reintroduces the
bug with no symptom at all. The failure is a check reporting SUCCESS, which is the family
`testing.guard-ships-with-mutation-proof` exists for.

**The mechanism, measured rather than asserted.** Measured on both platforms this suite runs on,
because the guard it replaces was fail-open for months on exactly the platform nobody measured:
macOS/git 2.55 (development) and Linux/git 2.47.3 (the `script-tests` runner host). Identical on
both — `GIT_DIR` exported, `show-toplevel` answering `<wt>/web`, the nested diff reporting exit 0.
The whole file was run green there, and the deletion mutation was witnessed red there:

  * Git exports `GIT_DIR` to `pre-push` **when the push comes from a worktree** — e.g.
    `GIT_DIR=/repo/.git/worktrees/wt`. From the main tree it exports nothing, which is why this
    never bites in a plain checkout and why it bites here constantly: `process.shared-tree-readonly`
    makes working in a worktree the mandated path, so the exported-`GIT_DIR` case is the NORMAL one.
  * With `GIT_DIR` set and `GIT_WORK_TREE` unset, git stops discovering the repo and takes the
    **current directory** as the work tree. `git rev-parse --show-toplevel` from `web/` answers
    `/repo/wt/web`.
  * So `pre-push`'s last line — `cd web && npm run check:api`, whose `check:api` ends in
    `git diff --exit-code` — compares against index paths that do not exist under that root. It
    reports **no diff and exits 0**. Generated-API drift ships, and the gate that exists to catch it
    prints success.

The test drives the REAL `.husky/pre-push` file, unedited, in a real worktree, with the environment
git really exports. What is substituted is only what surrounds it: the three `.claude/hooks` calls
are stubs (they are separately guarded and are not the subject), and `npm` is a stub on PATH whose
`run check:api` performs the nested `git diff --exit-code` that the real one ends in. The subject —
the ordering of the `unset` against the nested git call — is untouched.
"""

from __future__ import annotations

import os
import shutil
import stat
import subprocess
from pathlib import Path

REPO_ROOT = Path(__file__).resolve().parents[2]
PRE_PUSH = REPO_ROOT / ".husky" / "pre-push"

UNSET_CLAUSE = "unset GIT_DIR GIT_WORK_TREE GIT_INDEX_FILE"


# The hooks `pre-push` calls before the CI-parity block. Stubbed because each is guarded on its own
# terms and none of them is what this file is about — but DERIVED from the real file rather than
# hand-listed, so a hook added to `pre-push` tomorrow cannot leave this harness silently running a
# `pre-push` that dies at a missing script and calling that a red.
def _hook_calls(text: str) -> list[str]:
    """Every `.claude/hooks/` script `pre-push` actually invokes.

    Two refinements over a plain substring scan, each closing a way the harness would misreport:

      * **comment lines are skipped.** A comment naming a hook that no longer exists would otherwise
        redden `test_the_stub_hooks_are_derived_from_the_real_file` for a file that is perfectly
        correct.
      * **the prefix is not assumed to be `./`.** A hook invoked as `bash .claude/hooks/x.sh` would
        be missed, left unstubbed, and exit 127 — a NON-ZERO status that two tests here read as
        "drift was caught". That is a false green in the direction that matters, so the match is on
        the path segment rather than on `./`.
    """
    names = []
    for line in text.splitlines():
        # INLINE comments too, not just whole-line ones. Broadening the marker from `./.claude/hooks/`
        # to the path segment made a trailing `# ... .claude/hooks/removed-helper.sh` match, which
        # would redden this file for a `pre-push` that is perfectly correct — a false red the
        # narrower marker did not have. The fix for one over-match must not introduce another.
        stripped = line.split("#", 1)[0].strip()
        marker = ".claude/hooks/"
        if marker in stripped:
            rest = stripped.split(marker, 1)[1]
            names.append(rest.split()[0].rstrip("|&;\"'"))
    return names


def _git(cwd: Path, *args: str) -> str:
    return subprocess.run(
        ["git", *args],
        cwd=str(cwd),
        check=True,
        capture_output=True,
        text=True,
        env={
            **os.environ,
            "GIT_AUTHOR_NAME": "t",
            "GIT_AUTHOR_EMAIL": "t@e",
            "GIT_COMMITTER_NAME": "t",
            "GIT_COMMITTER_EMAIL": "t@e",
        },
    ).stdout.strip()


def _exe(path: Path, body: str) -> None:
    path.write_text(body)
    path.chmod(path.stat().st_mode | stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH)


class Bench:
    """A real repo, a real worktree, the real `pre-push`, and the env git really exports."""

    def __init__(self, tmp_path: Path, pre_push_text: str, *, drift: bool):
        tmp_path.mkdir(parents=True, exist_ok=True)
        self.root = tmp_path / "main-tree"
        self.root.mkdir()
        _git(self.root, "init", "-q", "-b", "main", ".")
        (self.root / "seed").write_text("seed\n")
        _git(self.root, "add", "seed")
        _git(self.root, "commit", "-qm", "init")

        self.wt = tmp_path / "wt"
        _git(self.root, "worktree", "add", "-q", str(self.wt), "-b", "feature")

        web = self.wt / "web"
        web.mkdir()
        (web / "gen.txt").write_text("generated\n")
        _git(self.wt, "add", "web/gen.txt")
        _git(self.wt, "commit", "-qm", "add generated file")
        if drift:
            # The condition `check:api` exists to catch: the committed generated artifact no longer
            # matches what regeneration produces.
            (web / "gen.txt").write_text("generated\nDRIFT\n")

        (self.wt / ".husky").mkdir()
        self.pre_push = self.wt / ".husky" / "pre-push"
        _exe(self.pre_push, pre_push_text)

        hooks = self.wt / ".claude" / "hooks"
        hooks.mkdir(parents=True)
        for name in _hook_calls(pre_push_text):
            _exe(hooks / name, "#!/usr/bin/env bash\ncat >/dev/null\nexit 0\n")

        # The npm stand-in. `run check:api` performs the nested `git diff --exit-code` the real
        # script ends in; everything else is a no-op. It records the nested diff's OWN exit code,
        # not merely that it ran. That distinction is load-bearing: one of the mutations below moves
        # the `unset` to the end of the file, which also makes the script's terminal status 0 (a
        # bare `unset` succeeds) — so asserting on pre-push's exit code alone would be satisfied for
        # a reason that has nothing to do with the nested git call. The recorded diff verdict IS the
        # defect; the script's exit code is downstream of it.
        self.witness = tmp_path / "check-api-ran"
        bindir = tmp_path / "bin"
        bindir.mkdir()
        _exe(
            bindir / "npm",
            "#!/usr/bin/env bash\n"
            'if [ "$1" = "run" ] && [ "$2" = "check:api" ]; then\n'
            "  git diff --exit-code -- gen.txt >/dev/null\n"
            "  _rc=$?\n"
            f'  echo "$PWD $_rc" >> "{self.witness}"\n'
            "  exit $_rc\n"
            "fi\n"
            "exit 0\n",
        )
        self.bindir = bindir
        # `GIT_DIR` exactly as git exports it for a push from this worktree, verified against a real
        # push in the investigation that produced this file.
        self.git_dir = _git(self.wt, "rev-parse", "--absolute-git-dir")

    def run(self, *, export_git_dir: bool) -> subprocess.CompletedProcess:
        env = {k: v for k, v in os.environ.items() if k not in ("GIT_DIR", "GIT_WORK_TREE", "GIT_INDEX_FILE")}
        env["PATH"] = f"{self.bindir}:{env['PATH']}"
        if export_git_dir:
            env["GIT_DIR"] = self.git_dir
        return subprocess.run(
            ["bash", str(self.pre_push), "origin", "file:///dev/null"],
            input=b"refs/heads/feature abc refs/heads/feature def\n",
            capture_output=True,
            cwd=str(self.wt),
            env=env,
            timeout=120,
        )

    def check_api_ran(self) -> bool:
        return self.witness.exists()

    def nested_diff_rc(self) -> int:
        """The exit code the nested `git diff --exit-code` actually reported.

        0 means it saw NO diff. With a drifted tree that answer is the bug.
        """
        assert self.witness.exists(), "check:api never ran, so there is no nested diff verdict"
        return int(self.witness.read_text().split()[-1])


# ------------------------------------------------------------------------------------------------
# ANTI-VACUITY — the clause exists, and the harness reaches the check that depends on it
# ------------------------------------------------------------------------------------------------


def test_the_unset_clause_is_still_in_pre_push():
    text = PRE_PUSH.read_text()
    assert UNSET_CLAUSE in text, (
        f"`{UNSET_CLAUSE}` is gone from .husky/pre-push. If it was removed deliberately, this file "
        "must be removed with it and docs/guard-inventory.md updated — do not delete this assertion "
        "on its own, it is the only thing pinning the ordering"
    )
    lines = text.splitlines()
    unset_at = next(i for i, ln in enumerate(lines) if UNSET_CLAUSE in ln)
    nested_at = next(i for i, ln in enumerate(lines) if "npm run check:api" in ln)
    assert unset_at < nested_at, (
        "the unset now comes AFTER the nested git call it exists to protect — that ordering is the "
        "regression, and it is silent"
    )


def test_the_harness_actually_reaches_check_api(tmp_path):
    bench = Bench(tmp_path, PRE_PUSH.read_text(), drift=True)
    bench.run(export_git_dir=False)
    assert bench.check_api_ran(), (
        "the CI-parity block never ran, so every exit code below would be reporting on the hooks "
        "before it rather than on the nested git call this file is about"
    )


# ------------------------------------------------------------------------------------------------
# THE GUARD DECIDES
# ------------------------------------------------------------------------------------------------


def test_drift_is_CAUGHT_with_no_git_env_exported(tmp_path):
    """Positive control: the harness detects real drift when nothing is in the way."""
    bench = Bench(tmp_path, PRE_PUSH.read_text(), drift=True)
    p = bench.run(export_git_dir=False)
    assert bench.nested_diff_rc() != 0, "the nested diff saw no drift even with a clean env"
    assert p.returncode != 0, f"the harness did not detect drift even with a clean env: {p.stderr!r}"


def test_drift_is_CAUGHT_when_git_exports_GIT_DIR_from_a_worktree(tmp_path):
    """THE REAL CASE. Every push from a worktree — the mandated way to work here — runs this."""
    bench = Bench(tmp_path, PRE_PUSH.read_text(), drift=True)
    p = bench.run(export_git_dir=True)
    assert bench.nested_diff_rc() != 0, (
        "the nested `git diff --exit-code` reported NO DIFF on a drifted file. That is the silent "
        "fail-open the `unset` exists to prevent, and it is invisible from the exit code alone"
    )
    assert p.returncode != 0, (
        "pre-push reported success on a drifted generated file while git had exported GIT_DIR: "
        f"{p.stdout!r} {p.stderr!r}"
    )


def test_a_CLEAN_tree_is_allowed_through(tmp_path):
    """Negative control. A harness that always failed would pass both assertions above."""
    bench = Bench(tmp_path, PRE_PUSH.read_text(), drift=False)
    p = bench.run(export_git_dir=True)
    assert p.returncode == 0, f"a clean tree was blocked: {p.stdout!r} {p.stderr!r}"
    assert bench.nested_diff_rc() == 0, "the nested diff invented a diff on a clean tree"


# ------------------------------------------------------------------------------------------------
# MUTATION PROOFS — the two ways the clause stops protecting anything
# ------------------------------------------------------------------------------------------------


def _positive_control(tmp_path: Path, label: str) -> None:
    bench = Bench(tmp_path / f"pc-{label}", PRE_PUSH.read_text(), drift=True)
    p = bench.run(export_git_dir=True)
    assert bench.nested_diff_rc() != 0 and p.returncode != 0, (
        "the UNMUTATED pre-push did not catch the drift, so 'the mutant lets it through' proves "
        f"nothing about the clause: {p.stdout!r} {p.stderr!r}"
    )


def test_MUTATION_DELETING_the_unset_lets_drift_through_silently(tmp_path):
    _positive_control(tmp_path, "delete")

    text = PRE_PUSH.read_text()
    assert UNSET_CLAUSE in text, "retarget this mutation; the clause has moved"
    mutated = text.replace(UNSET_CLAUSE, "# clause removed by the mutation proof", 1)

    bench = Bench(tmp_path / "mut", mutated, drift=True)
    p = bench.run(export_git_dir=True)
    assert bench.check_api_ran(), "the mutant died before check:api, so its exit code says nothing"
    assert bench.nested_diff_rc() == 0, (
        "removing the unset did NOT blind the nested diff, so the clause is not what protects it "
        "and this whole file is pinning the wrong thing"
    )
    assert p.returncode == 0, f"the drift was still caught somehow: {p.stdout!r}"


def test_MUTATION_REORDERING_the_unset_after_the_nested_git_call_lets_drift_through(tmp_path):
    """The regression ersatztv#785 names by hand: not deletion, relocation.

    Deleting a line is a conspicuous diff. Moving it — during a tidy-up, or when a new check is
    appended above it — reads as a no-op and is not.

    This asserts on the NESTED DIFF's verdict, not on pre-push's exit code. Relocating the `unset`
    to the end of the file also makes it the script's last statement, and a bare `unset` succeeds —
    so `returncode == 0` would hold here even if the nested git call had worked perfectly. That is a
    test passing for the wrong reason.
    """
    _positive_control(tmp_path, "reorder")

    lines = PRE_PUSH.read_text().splitlines()
    kept = [ln for ln in lines if UNSET_CLAUSE not in ln]
    assert len(kept) == len(lines) - 1, "expected exactly one unset line to relocate"
    mutated = "\n".join(kept + [UNSET_CLAUSE, ""])

    bench = Bench(tmp_path / "mut", mutated, drift=True)
    bench.run(export_git_dir=True)
    assert bench.check_api_ran(), "the mutant died before check:api, so it reports on nothing"
    assert bench.nested_diff_rc() == 0, (
        "moving the unset below the nested git call did NOT blind it, so the ORDERING is not "
        "load-bearing and the ordering assertion in the anti-vacuity test is decoration"
    )


def test_the_stub_hooks_are_derived_from_the_real_file():
    """If `pre-push` gains a hook call, the harness must stub it rather than die at a missing file.

    A `pre-push` that exits 127 at a missing script produces a non-zero exit — indistinguishable
    from 'drift was caught' in two of the tests above.
    """
    calls = _hook_calls(PRE_PUSH.read_text())
    assert calls, "no ./.claude/hooks/ call found in pre-push; the extractor has stopped matching"
    for name in calls:
        assert (REPO_ROOT / ".claude" / "hooks" / name).is_file(), (
            f"pre-push calls {name}, which does not exist in .claude/hooks/"
        )


def test_shutil_which_npm_is_not_what_the_harness_used(tmp_path):
    """Anti-vacuity for the stand-in: a real `npm` on PATH would run the real scripts and pass."""
    bench = Bench(tmp_path, PRE_PUSH.read_text(), drift=True)
    resolved = shutil.which("npm", path=f"{bench.bindir}:{os.environ['PATH']}")
    assert resolved == str(bench.bindir / "npm"), (
        f"the harness would have used {resolved}, not its stand-in — the check it performs would "
        "then be whatever the real package.json says, not the nested git call under test"
    )