5 files changed, 81 insertions, 7 deletions

diff --git a/src/qml/common/qqmlsignalnames.cpp b/src/qml/common/qqmlsignalnames.cpp
index e66c26d4e2..d2a23205a6 100644
--- a/src/qml/common/qqmlsignalnames.cpp
+++ b/src/qml/common/qqmlsignalnames.cpp
@@ -191,6 +191,25 @@ std::optional<QString> QQmlSignalNames::handlerNameToSignalName(QStringView hand
 
 /*!
 \internal
+Returns a signal name from \a handlerName string. Do not use it on changed handlers, see
+changedHandlerNameToSignalName for that! Accepts improperly capitalized handler names and
+incorrectly resolves signal names that start with '_' or '$'.
+*/
+std::optional<QString> QQmlSignalNames::badHandlerNameToSignalName(QStringView handler)
+{
+    if (handler.size() <= StrlenOn || !handler.startsWith(On))
+        return {};
+
+    QString signalName = handler.sliced(StrlenOn).toString();
+
+    // This is quite wrong. But we need it for backwards compatibility.
+    signalName.front() = signalName.front().toLower();
+
+    return signalName;
+}
+
+/*!
+\internal
 Returns a signal name from \a changedHandlerName string. Makes sure not to lowercase the 'C' from
 Changed.
 */
diff --git a/src/qml/common/qqmlsignalnames_p.h b/src/qml/common/qqmlsignalnames_p.h
index 753f2ca97a..9c3d192666 100644
--- a/src/qml/common/qqmlsignalnames_p.h
+++ b/src/qml/common/qqmlsignalnames_p.h
@@ -49,6 +49,9 @@ public:
     static bool isHandlerName(QStringView signalName);
 
     static QString addPrefixToPropertyName(QStringView prefix, QStringView propertyName);
+
+    // ### Qt7: remove this
+    static std::optional<QString> badHandlerNameToSignalName(QStringView handler);
 };
 
 QT_END_NAMESPACE
diff --git a/src/qml/qml/qqmlproperty.cpp b/src/qml/qml/qqmlproperty.cpp
index 7437eefa85..099512192f 100644
--- a/src/qml/qml/qqmlproperty.cpp
+++ b/src/qml/qml/qqmlproperty.cpp
@@ -381,11 +381,11 @@ void QQmlPropertyPrivate::initProperty(QObject *obj, const QString &name,
     };
 
     const QString terminalString = terminal.toString();
-    if (auto signalName = QQmlSignalNames::handlerNameToSignalName(terminalString)) {
+    const auto findSignal = [&](const QString &signalName) {
         if (ddata && ddata->propertyCache) {
             // Try method
-            const QQmlPropertyData *d =
-                    ddata->propertyCache->property(*signalName, currentObject, context);
+            const QQmlPropertyData *d
+                    = ddata->propertyCache->property(signalName, currentObject, context);
 
             // ### Qt7: This code treats methods as signals. It should use d->isSignal().
             //          That would be a change in behavior, though. Right now you can construct a
@@ -396,13 +396,29 @@ void QQmlPropertyPrivate::initProperty(QObject *obj, const QString &name,
             if (d) {
                 object = currentObject;
                 core = *d;
-                return;
+                return true;
             }
 
-            if (findChangeSignal(terminalString))
-                return;
-        } else if (findSignalInMetaObject(signalName->toUtf8())) {
+            return findChangeSignal(terminalString);
+        }
+
+        return findSignalInMetaObject(signalName.toUtf8());
+    };
+
+    auto signalName = QQmlSignalNames::handlerNameToSignalName(terminalString);
+    if (signalName) {
+        if (findSignal(*signalName))
             return;
+    } else {
+        signalName = QQmlSignalNames::badHandlerNameToSignalName(terminalString);
+        if (signalName) {
+            qWarning()
+                    << terminalString
+                    << "is not a properly capitalized signal handler name."
+                    << QQmlSignalNames::signalNameToHandlerName(*signalName)
+                    << "would be correct.";
+            if (findSignal(*signalName))
+                return;
         }
     }
 
diff --git a/tests/auto/qml/qqmlconnections/data/badSignalHandlerName.qml b/tests/auto/qml/qqmlconnections/data/badSignalHandlerName.qml
new file mode 100644
index 0000000000..921787aa36
--- /dev/null
+++ b/tests/auto/qml/qqmlconnections/data/badSignalHandlerName.qml
@@ -0,0 +1,15 @@
+import QtQml
+
+QtObject {
+    id: root
+    signal _foo
+
+    property int handled: 0
+
+    property Connections c: Connections {
+        target: root
+        function on_Foo() { root.handled += 1 }
+        function on_foo() { root.handled += 2 }
+    }
+}
+
diff --git a/tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp b/tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp
index 61102798e7..adbaffb1ce 100644
--- a/tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp
+++ b/tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp
@@ -55,6 +55,7 @@ private slots:
     void bindToPropertyWithUnderscoreChangeHandler();
     void invalidTarget();
 
+    void badSignalHandlerName();
 private:
     QQmlEngine engine;
     void prefixes();
@@ -461,6 +462,26 @@ void tst_qqmlconnections::invalidTarget()
     QTRY_VERIFY(root->objectName().isEmpty());
 }
 
+void tst_qqmlconnections::badSignalHandlerName()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("badSignalHandlerName.qml"));
+    QVERIFY2(component.isReady(), qPrintable(component.errorString()));
+
+    QTest::ignoreMessage(
+            QtWarningMsg,
+            "\"on_foo\" is not a properly capitalized signal handler name. "
+            "\"on_Foo\" would be correct.");
+
+    QScopedPointer<QObject> root(component.create());
+    QVERIFY(!root.isNull());
+
+    QCOMPARE(root->property("handled").toInt(), 0);
+    QMetaObject::invokeMethod(root.data(), "_foo");
+    QCOMPARE(root->property("handled").toInt(), 3);
+}
+
+
 QTEST_MAIN(tst_qqmlconnections)
 
 #include "tst_qqmlconnections.moc"