Put MediaPlayer's error handler back in Qt 5 spelling, and teach the generator the rename

The Android app has been coming up with an empty window since c3bd6e8, and not because of
anything to do with a bike. Home.qml assigns onErrorOccurred, which is Qt 6's name for
MediaPlayer's error signal. Qt 5.15 has no such property, and assigning to one that does
not exist is a load error rather than a warning - so Home.qml never instantiates,
StackView is left with no initialItem, and the window is blank while the app runs
perfectly well behind it. The device log says it in one line:

  qrc:/main.qml:1420:9: QML StackView: initialItem: qrc:/Home.qml:625
      Cannot assign to non-existent property "onErrorOccurred"

and then says it again in the consequences: rootItem undefined all over HomeForm.ui.qml,
and homeform's constructor connecting its QML signals to (nullptr) eight times over,
because rootObject->findChild("home") found nothing to connect to.

tools/qt6-qml-imports.py already carries the rule this broke, in its own docstring: the
sources are Qt 5, because Qt 5 is what Android and every other shipping target build, and
the Qt 6 variants are generated. Imports were the only difference it knew about. Renamed
signal handlers are a second, so it now rewrites those too - anchored to the start of a
line and matched with its colon, so the same word in a comment is left alone.

The body becomes a plain function expression rather than either version's parameter
syntax, because Qt 5 injects signal parameters and Qt 6 removed injection, and a function
is the one form both bind correctly.

videoOutput, which the same commit introduced, needs no such treatment: Qt 5.15's own type
registration lists it at revision 15, and the device log never complained about it. The
error was always just the one property.

Verified on Qt 5.15 by running the app: the load error is gone, and the eight
connect-to-nullptr failures are zero, which is the same thing said from the C++ side -
Home.qml loads and findChild("home") finds it. Checked the other direction too, by running
the generator over the fixed source and confirming the Qt 6 output carries
onErrorOccurred, so the Windows build keeps what c3bd6e8 gave it.

src/videoPlayback.qml carried the same two lines and gets the same change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019d4Hga7UGcxmcG88pwcSCV

Author: claude

src/Home.qml

@@ -611,18 +611,26 @@ HomeForm {
                 }
             }
 
-            // Qt 6 renamed the error signal to errorOccurred() and reversed how the
-            // sink is attached: the player names its videoOutput rather than the
-            // VideoOutput naming its source. Assigning to the old onError is a load
-            // error, not a warning - it takes Home.qml with it, and StackView then
-            // has no initialItem, which is why the window came up empty.
+            // Qt 6 renamed this signal from error() to errorOccurred(). The Qt 5
+            // spelling is the one that belongs here - these sources are Qt 5 and the
+            // Qt 6 variants are generated (tools/qt6-qml-imports.py, which does the
+            // rename) - because Qt 5.15 has no errorOccurred and rejects the
+            // assignment outright. That is a load error rather than a warning, so it
+            // takes Home.qml with it, StackView is left with no initialItem, and the
+            // Android window comes up empty with the app running fine underneath.
+            //
+            // The body is a function expression rather than either version's parameter
+            // syntax: Qt 5 injects signal parameters and Qt 6 removed injection, and a
+            // plain function is the one form both bind correctly.
+            //
+            // videoOutput needs no such care - it exists in Qt 5.15 too (revision 15).
             MediaPlayer {
                 id: videoPlaybackHalf
                 objectName: "videoplaybackhalf"
                 playbackRate: rootItem.videoRate
                 videoOutput: videoPlayer
 
-                onErrorOccurred: (error, errorString) => {
+                onError: function(error, errorString) {
                     if (MediaPlayer.NoError !== error) {
                         console.log("[qmlvideo] MediaPlayer error " + error + " errorString " + errorString)
                     }

src/videoPlayback.qml

@@ -22,7 +22,7 @@ Rectangle {
            playbackRate: rootItem.videoRate
            videoOutput: videoPlayer
 
-           onErrorOccurred: (error, errorString) => {
+           onError: function(error, errorString) {
                if (MediaPlayer.NoError !== error) {
                    console.log("[qmlvideo] MediaPlayer error " + error + " errorString " + errorString)
                }

tools/qt6-qml-imports.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Rewrite the QML import lines for a Qt 6 build.
+"""Rewrite the QML imports, and the handful of renamed signal handlers, for a Qt 6 build.
 
 The .qml sources are written for Qt 5, which is what Android, iOS and every other
 shipping target build with. Qt 5.15 refuses a library import that carries no
@@ -40,6 +40,19 @@
 # QtQuick, QtQuick.Controls, QtQuick.Layouts and QtQuick.Window are deliberately
 # absent from both tables: Qt 6 still accepts their 2.x imports.
 
+# Signal handlers Qt 6 renamed. Same principle as the imports: the Qt 5 spelling is
+# what the sources carry, because Qt 5 is what ships, and Qt 6 is generated.
+#
+# MediaPlayer's error() became errorOccurred(). Writing the Qt 6 name in the source
+# instead does not degrade gracefully - Qt 5.15 has no such property, so assigning to
+# it is a *load* error that takes the whole file with it. When that file is Home.qml,
+# StackView has no initialItem and the Android app comes up with an empty window and
+# no clue as to why. That is not hypothetical; it shipped, and cost an evening.
+#
+# Anchored to the start of a line so a mention inside a string or a comment is left
+# alone, and matched with the colon so it is a handler and not a word.
+HANDLER_RENAME = {"onError": "onErrorOccurred"}
+
 VERSION = r"[0-9]+(?:\.[0-9]+)?"
 
 
@@ -56,6 +69,12 @@ def rewrite(text):
             r"\g<1>",
             text,
         )
+    for handler, replacement in HANDLER_RENAME.items():
+        text = re.sub(
+            rf"(?m)^(\s*){re.escape(handler)}(\s*:)",
+            rf"\g<1>{replacement}\g<2>",
+            text,
+        )
     return text