fix(hud): keep a due message timer off a cleared closure

negpy/desktop/view/canvas/hud.py

@@ -123,7 +123,9 @@ def __init__(self, parent=None):
 
         self._message_timer = QTimer(self)
         self._message_timer.setSingleShot(True)
-        self._message_timer.timeout.connect(lambda: self.showMessage(""))
+        # A bound method, not a lambda: a collection on another thread clears a closure and defers the
+        # widget's delete, so a due timer would call a function with no closure.
+        self._message_timer.timeout.connect(self._expire_message)
         self._progress_timer = QTimer(self)
         self._progress_timer.setSingleShot(True)
         self._progress_timer.timeout.connect(self.hide_progress)
@@ -160,6 +162,9 @@ def showMessage(self, text: str, timeout: int = 0, kind: str = "info") -> None:
             self._message_timer.start(timeout or _DEFAULT_MESSAGE_MS)
         self._sync()
 
+    def _expire_message(self) -> None:
+        self.showMessage("")
+
     def clear_message(self, text: str) -> None:
         """Clears the message only if it is still `text`, so a later message survives."""
         if text and self.message.text() == text and not self.message.isHidden():

negpy/desktop/view/sidebar/pick_better_window.py

@@ -106,7 +106,7 @@ def __init__(self, parent=None) -> None:
         self._move_label.setAttribute(Qt.WidgetAttribute.WA_TransparentForMouseEvents)
         self._move_timer = QTimer(self)
         self._move_timer.setSingleShot(True)
-        self._move_timer.timeout.connect(lambda: self._move_label.setText(""))
+        self._move_timer.timeout.connect(self._move_label.clear)
 
         # The photos inset from the panel's top by the reserved band — the move summary, the in-flight
         # name and the A/Skip/B captions — so a caption that hugs a photo's top edge sits clear of

tests/test_canvas_hud.py

@@ -1,3 +1,8 @@
+import os
+import subprocess
+import sys
+from pathlib import Path
+
 from PyQt6.QtGui import QColor
 from PyQt6.QtWidgets import QWidget
 
@@ -14,6 +19,43 @@ def _hud(width=1200):
     return hud
 
 
+_DUE_TIMER_AFTER_A_BACKGROUND_COLLECTION = """
+import gc, threading, time
+from PyQt6.QtTest import QTest
+from PyQt6.QtWidgets import QApplication, QWidget
+from negpy.desktop.view.canvas.hud import CanvasHud
+
+app = QApplication([])
+gc.disable()
+
+def strip():
+    parent = QWidget()
+    hud = CanvasHud(parent)
+    hud.showMessage("x", 20)
+    hud._keepalive = parent
+
+strip()
+thread = threading.Thread(target=gc.collect)
+thread.start()
+thread.join()
+time.sleep(0.05)
+QTest.qWait(30)
+"""
+
+
+def test_a_message_timer_survives_a_collection_on_another_thread():
+    # In a subprocess: the failure is a segfault, which would end the test run.
+    run = subprocess.run(
+        [sys.executable, "-c", _DUE_TIMER_AFTER_A_BACKGROUND_COLLECTION],
+        capture_output=True,
+        text=True,
+        timeout=60,
+        cwd=Path(__file__).parent.parent,
+        env={**os.environ, "QT_QPA_PLATFORM": "offscreen"},
+    )
+    assert run.returncode == 0, run.stderr
+
+
 def test_an_empty_strip_hides_so_the_canvas_keeps_its_height(qapp):
     hud = _hud()
     assert hud.isHidden()