utils/gatelock/gatelock/_grabwatch.py
Krzysztof kuhy Rudnicki 02659e0abf
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gatelock: split _recovery.py and _surfaces.py, and fix two fail-open guards
_recovery.py  321 -> 242 + _recovery_types 47 + _grabwatch 84
  _surfaces.py  380 -> 250 + _placement 136 + _surface_types 54 + _textmirror 70

Two guards had to be repaired first, because both would have gone quiet
rather than red:

1. palette-drift CI was ALREADY BROKEN by the earlier _window.py split.
   palette_check.py reads LockConfig's colour defaults from a hardcoded
   gatelock/_window.py, and LockConfig had moved to _config.py — so it parsed
   0 tk tokens and reported "10 failing check(s)" where HEAD reports 0. Fixed
   the path, and made parse_tk raise instead of returning {} when LockConfig
   is not found: the empty dict is what let every tk comparison pass
   vacuously while the drift guard was off for the whole stack.

2. test_recovery_invariants' symbols() read one hardcoded filename, so
   splitting _recovery.py would have narrowed the "no weakening call"
   invariant — the one that exists because of the 2026-07-25 unlock — to
   whichever half kept the name, with the suite still green. It now globs the
   whole _recovery*/_surfaces* family and fails if the glob matches nothing.
   Verified it discriminates: a throwaway _recovery_probe.py calling
   restore_vt_switching made the test fail, and removing it restored green.

GrabWatch is a small object rather than a free function because holds_grab
and its once-per-cause warning share state; _placement holds the geometry
questions and the re-assertion pass, which can only ever add visibility.
_surfaces keeps an explicit __all__: the autofixer pruned the mirror_text_widgets
re-export once and `import gatelock` broke, so the intent is now stated.

389 passed at 100% branch coverage; gatelock.__all__ is the same 58 names as
HEAD; palette_check back to 0 failing checks.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CFSGeWxHPY5rHUGrPqhcmG
2026-08-22 15:08:50 +02:00

85 lines
3.4 KiB
Python

"""Deciding whether this application still holds the input grab.
Split from :mod:`gatelock._recovery`, which re-asserts the grab when this
says it is gone. The question is subtle enough -- and its history costly
enough -- to be worth reading on its own, and the log-throttling state it
needs is the reason it is a small object rather than a function.
"""
from __future__ import annotations
import logging
import tkinter as tk
_logger = logging.getLogger(__name__)
class GrabWatch:
"""Answers "is the grab still ours?", warning once per distinct cause."""
def __init__(self, root: tk.Misc) -> None:
"""Watch the grab on `root`'s display.
Args:
root: The Tk widget whose display the grab is read from.
"""
self._root = root
self._last_warning: str | None = None
def holds_grab(self) -> bool:
"""Whether the grab is held by a window this application owns.
Deliberately *not* ``grab_current() is self._root``. Our own transient
children take the grab for themselves: a posted Tk menu grabs the menu
window, and the old identity test read that as "the grab was lost" and
called ``grab_set_global()`` a second later, stealing it back off our
own widget mid-interaction. That is what made the screen-locker sport
selector unusable while locked on 2026-07-26. Any window we own still
means the lock has the pointer and keyboard.
``grab_current`` resolves the name Tcl gives it against our own widget
map, so anything that does not resolve -- a Tcl-created popdown such as
a ``ttk.Combobox``'s, or a stale name -- raises ``KeyError`` and is NOT
provably ours. That counts as lost and the grab is re-taken: fail
closed, because this module exists to keep the lock, and losing a
popdown beats believing we hold a grab we do not.
Known limitation: a second ``tk.Tk()`` in the same process reports its
root as ``"."`` too, which is indistinguishable from ours. The old
identity test had exactly the same blind spot. ``_heat_skip``'s
throwaway root is the only other one in screen-locker, and it is
destroyed before the lock window exists.
Returns:
True while a window we own holds the grab.
"""
try:
held = self._root.grab_current() is not None
except KeyError as exc:
self.warn_once(
f"the grab is held by {exc.args[0]!r}, not one of our windows"
)
return False
except tk.TclError:
self.warn_once("could not read the current grab")
return False
if held:
self._last_warning = None
return held
def warn_once(self, reason: str) -> None:
"""Warn about a lost grab, but only when the reason changes.
These states can persist for the whole lock (a dark display, a popdown
that keeps re-grabbing), and this runs once a second -- warning every
tick would push a line per second into the journal for as long as it
lasts. Silence is not the alternative: the first occurrence and every
change of cause are still logged at WARNING.
Args:
reason: Why the grab is not provably ours.
"""
if reason != self._last_warning:
_logger.warning("%s; treating it as lost and re-taking it", reason)
self._last_warning = reason