Reject Windows-style git hooks paths instead of creating a junk dir (#1385)

On WSL/POSIX, Path("C:\\...").is_absolute() is False, so a Windows absolute
core.hooksPath (or rev-parse --git-path output) was joined under the repo root
and mkdir'd as a literal backslash-named junk directory while install reported
success and the real .git/hooks got nothing. Both branches of _hooks_dir now
reject drive-letter / backslash paths with a clear error so the failure is loud.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

graphify/hooks.py

@@ -284,6 +284,25 @@ def _git_root(path: Path) -> Path | None:
     return None
 
 
+_WINDOWS_DRIVE_RE = re.compile(r"^[A-Za-z]:[\\/]")
+
+
+def _reject_windows_path(value: str, source: str) -> None:
+    """Raise if a hooks path looks like a Windows absolute path (#1385).
+
+    On POSIX/WSL ``Path("C:\\Users\\...").is_absolute()`` is False, so an absolute
+    Windows hooks path gets joined under the repo root and mkdir'd as a literal
+    junk directory (backslashes and all), while install reports success and the
+    real ``.git/hooks`` gets nothing. Fail loudly instead so the user can fix it.
+    """
+    if _WINDOWS_DRIVE_RE.match(value) or "\\" in value:
+        raise RuntimeError(
+            f"git hooks path from {source} looks like a Windows path: {value!r}. "
+            f"On WSL/POSIX this can't resolve to a real directory. Unset it with "
+            f"`git config --local --unset core.hooksPath`, or set a POSIX path."
+        )
+
+
 def _hooks_dir(root: Path) -> Path:
     """Return the git hooks directory, respecting core.hooksPath if set (e.g. Husky)."""
     try:
@@ -292,6 +311,7 @@ def _hooks_dir(root: Path) -> Path:
         # configparser lowercases option names; git's hooksPath becomes hookspath
         custom = cfg.get("core", "hookspath", fallback="").strip()
         if custom:
+            _reject_windows_path(custom, "core.hooksPath")
             p = Path(custom).expanduser()
             if not p.is_absolute():
                 p = root / p
@@ -331,6 +351,7 @@ def _hooks_dir(root: Path) -> Path:
         # A valid hooks path can never contain newlines or NUL. Their presence
         # means git echoed an unrecognised flag back (old git behaviour).
         if res.returncode == 0 and raw and not any(c in raw for c in ("\n", "\r", "\x00")):
+            _reject_windows_path(raw, "git rev-parse --git-path hooks")
             d = (root / raw).resolve()
             d.mkdir(parents=True, exist_ok=True)
             return d

tests/test_hooks.py

@@ -333,3 +333,44 @@ def test_installed_hooks_contain_no_nohup(tmp_path):
         text = (repo / ".git" / "hooks" / name).read_text(encoding="utf-8")
         assert "nohup" not in text, f"installed {name} still references nohup"
         assert "start_new_session=True" in text
+
+
+# ── #1385: reject Windows-style hooks paths instead of creating a junk dir ───
+
+def _set_hookspath(repo: Path, value: str) -> None:
+    subprocess.run(["git", "-C", str(repo), "config", "--local", "core.hooksPath", value],
+                   check=True, capture_output=True)
+
+
+@pytest.mark.parametrize("winpath", [
+    r"C:\Users\u\repo\.git\hooks",
+    r"c:/Users/u/.git/hooks",
+    r"D:\hooks",
+    r"some\back\slashed\path",
+])
+def test_windows_hookspath_rejected_no_junk_dir(tmp_path, winpath):
+    """A Windows-style core.hooksPath must raise (loud failure), not silently
+    create a backslash-named junk directory and report success (#1385)."""
+    repo = _make_git_repo(tmp_path)
+    _set_hookspath(repo, winpath)
+    with pytest.raises(RuntimeError, match="Windows path"):
+        install(repo)
+    # no junk directory got created anywhere under the repo
+    junk = [p for p in repo.rglob("*") if "\\" in p.name or p.name.startswith(("C:", "c:", "D:"))]
+    assert junk == [], f"junk dir created: {junk}"
+
+
+def test_posix_custom_hookspath_still_works(tmp_path):
+    """A legitimate POSIX core.hooksPath (Husky-style) must still install."""
+    repo = _make_git_repo(tmp_path)
+    _set_hookspath(repo, ".husky")
+    msg = install(repo)
+    assert "post-commit" in msg
+    assert (repo / ".husky" / "post-commit").exists()
+
+
+def test_default_hooks_dir_unaffected(tmp_path):
+    """No core.hooksPath -> normal .git/hooks install, no rejection."""
+    repo = _make_git_repo(tmp_path)
+    install(repo)
+    assert (repo / ".git" / "hooks" / "post-commit").exists()