v0.20.6: one press, sixteen hundred songs

A single Right-arrow press skipped 1,676 tracks in 81 s and hard-froze the
desktop. On Wayland key repeat is generated by the client until the
compositor delivers the release, and the key filter treated every repeat as
a new press. Each skip sent gnome-shell an MPRIS Metadata whose xesam:artist
was a plain Python list, which marshals as "av" instead of "as". gnome-shell
logged an error for every one (50k/min) and reloaded the cover, and that load
is what kept it from ever delivering the release.

Space/Left/Right now act once per press and swallow the repeats.
xesam:artist goes out through mpris.string_array, which build_properties_changed
now shares for invalidated_properties. The new test round-trips the signal
into GDBus, which is what gnome-shell validates with, and fails 'av' == 'as'
against the old code.

lintunes/__init__.py

@@ -1,3 +1,3 @@
 """LinTunes — iTunes-style music library manager and player for Linux."""
 
-__version__ = "0.20.5"
+__version__ = "0.20.6"

lintunes/gui/main_window.py

@@ -1626,6 +1626,15 @@ class MainWindow(QMainWindow):
                                   QAbstractSpinBox, QComboBox)):
                 return False
             key = event.key()
+            if key in (Qt.Key.Key_Space, Qt.Key.Key_Right, Qt.Key.Key_Left) \
+                    and event.isAutoRepeat():
+                # On Wayland key repeat is generated client-side until the
+                # compositor delivers the release — and a compositor busy
+                # with our own MPRIS churn delivers it late, so one held
+                # arrow became 1,676 track skips (Round 56). A transport key
+                # acts once per press; the repeats are swallowed so they
+                # don't fall through and move the table's cursor either.
+                return True
             if key == Qt.Key.Key_Space:
                 self._log_key(event, "space")
                 self.play_pause()

lintunes/mpris.py

@@ -259,7 +259,7 @@ class MprisPlayerAdaptor(QDBusAbstractAdaptor):
         meta = {
             "mpris:trackid": QDBusObjectPath(f"/org/lintunes/track/{track.track_id}"),
             "xesam:title": track.name or "",
-            "xesam:artist": [track.artist or ""],
+            "xesam:artist": string_array([track.artist or ""]),
             "xesam:album": track.album or "",
         }
         if track.total_time:
@@ -275,17 +275,31 @@ class MprisPlayerAdaptor(QDBusAbstractAdaptor):
         QDBusConnection.sessionBus().send(build_properties_changed(changed))
 
 
+def string_array(values) -> QDBusArgument:
+    """A D-Bus string array ("as"). A plain Python list of str marshals as
+    "av", which GDBus consumers validate and reject — see
+    build_properties_changed and xesam:artist in _metadata."""
+    string_id = QMetaType(QMetaType.Type.QString.value).id()
+    arg = QDBusArgument()
+    arg.beginArray(string_id)
+    for value in values:
+        arg.add(value, string_id)
+    arg.endArray()
+    return arg
+
+
 def build_properties_changed(changed: dict) -> QDBusMessage:
     """A spec-correct Properties.PropertiesChanged signal for the Player
     interface. invalidated_properties must be marshalled as a D-Bus string
     array ("as"); a plain Python [] goes over as "av", and GDBus consumers —
     including gsd-media-keys, which keys its media-key MRU on seeing
     PlaybackStatus change — validate the signature and drop the signal.
-    (Same pitfall as reveal_paths in track_table.)"""
+    (Same pitfall as reveal_paths in track_table, and as xesam:artist inside
+    Metadata: sent as "av", gnome-shell logged an error and reloaded the
+    cover per track change, and during a runaway key repeat that flood is
+    what froze the desktop — Round 56.)"""
     msg = QDBusMessage.createSignal(
         OBJECT_PATH, "org.freedesktop.DBus.Properties", "PropertiesChanged")
-    invalidated = QDBusArgument()
-    invalidated.beginArray(QMetaType(QMetaType.Type.QString.value).id())
-    invalidated.endArray()
-    msg.setArguments(["org.mpris.MediaPlayer2.Player", changed, invalidated])
+    msg.setArguments(["org.mpris.MediaPlayer2.Player", changed,
+                      string_array([])])
     return msg