Improve "Cannot assign object to list property" error message

Before:

    Cannot assign object to list property "animations"

After:

    Cannot assign object of type "QQuickFrameAnimation" to list property "animations"; expected "QQuickAbstractAnimation*"

Fixes: QTBUG-137469
Pick-to: 6.5 6.8 6.9 6.10
Change-Id: Iddf52d4262720236ffc610b6f7326bb126c53509
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/qml/qml/qqmlpropertyvalidator.cpp

@@ -732,7 +732,10 @@ QQmlError QQmlPropertyValidator::validateObjectBinding(const QQmlPropertyData *p
         if (!QQmlMetaType::isInterface(listType)) {
             QQmlPropertyCache::ConstPtr source = propertyCaches.at(binding->value.objectIndex);
             if (!canCoerce(listType, source)) {
-                return qQmlCompileError(binding->valueLocation, tr("Cannot assign object to list property \"%1\"").arg(propertyName));
+                const QString expectedTypeName = QString::fromUtf8(listType.name()).remove(QLatin1Char('*'));
+                return qQmlCompileError(binding->valueLocation,
+                    tr("Cannot assign object of type \"%1\" to list property \"%2\"; expected \"%3\"")
+                        .arg(source->className(), propertyName, expectedTypeName));
             }
         }
         return noError;

tests/auto/qml/qqmllanguage/data/assignWrongTypeToObjectList.qml

@@ -0,0 +1,5 @@
+import QtQuick
+
+SequentialAnimation {
+    FrameAnimation {}
+}

tests/auto/qml/qqmllanguage/data/badListItemType.errors.txt

@@ -1 +1 @@
-4:15:Cannot assign object to list property "children"
+4:15:Cannot assign object of type "QQmlComponent" to list property "children"; expected "QQuickItem"

tests/auto/qml/qqmllanguage/data/listAssignment.1.errors.txt

@@ -1 +1 @@
-4:24:Cannot assign object to list property "containerChildren"
+4:24:Cannot assign object of type "QObject" to list property "containerChildren"; expected "MyContainer"

tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp

@@ -529,6 +529,8 @@ private slots:
 
     void enumTypeAnnotations();
 
+    void assignWrongTypeToObjectList();
+
 private:
     QQmlEngine engine;
     QStringList defaultImportPathList;
@@ -8984,8 +8986,8 @@ void tst_qqmllanguage::overrideDefaultProperty()
 
     QQmlComponent c(&e, url);
     QVERIFY(c.isError());
-    QCOMPARE(c.errorString(),
-             url.toString() + QLatin1String(":5 Cannot assign object to list property \"data\"\n"));
+    QCOMPARE(c.errorString(), url.toString() + QLatin1String(
+        ":5 Cannot assign object of type \"QQuickItem\" to list property \"data\"; expected \"QVariant\"\n"));
 }
 
 void tst_qqmllanguage::enumScopes()
@@ -10036,6 +10038,15 @@ void tst_qqmllanguage::enumTypeAnnotations()
     QVERIFY(!o.isNull());
 }
 
+void tst_qqmllanguage::assignWrongTypeToObjectList()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("assignWrongTypeToObjectList.qml"));
+    QVERIFY(!component.isReady());
+    QVERIFY(QRegularExpression(".*Cannot assign object of type \"QQuickFrameAnimation\""_L1
+        + " to list property \"animations\"; expected \"QQuickAbstractAnimation\""_L1).match(component.errorString()).hasMatch());
+}
+
 QTEST_MAIN(tst_qqmllanguage)
 
 #include "tst_qqmllanguage.moc"