Replace signal name manipulations with QQmlSignalNames

Remove custom implementations found in qqmljs* and use the
static helper methods from qqmlsignalnames_p.h instead. This sometimes
requires to move some code around to avoid bugs with property that do
not have letters in their name.
Add a warning in the JS implementation of the SignalSpy.qml that the
used heuristic might fail on certain signal names.
Add tests in in tst_qqmllanguage to see if the property change handlers
work correctly for weird names.

Change-Id: I4dc73c34df7f77f529511fa04ab5fcc5385b59fc
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

34 files changed, 293 insertions, 246 deletions

diff --git a/src/plugins/qmltooling/qmldbg_debugger/qqmlenginedebugservice.cpp b/src/plugins/qmltooling/qmldbg_debugger/qqmlenginedebugservice.cpp
index 1fcc1e7772..3bd37878a8 100644
--- a/src/plugins/qmltooling/qmldbg_debugger/qqmlenginedebugservice.cpp
+++ b/src/plugins/qmltooling/qmldbg_debugger/qqmlenginedebugservice.cpp
@@ -15,6 +15,7 @@
 #include <private/qqmlvaluetype_p.h>
 #include <private/qqmlvmemetaobject_p.h>
 #include <private/qqmlexpression_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 #include <QtCore/qdebug.h>
 #include <QtCore/qmetaobject.h>
@@ -119,22 +120,14 @@ QDataStream &operator>>(QDataStream &ds,
     return ds;
 }
 
-static inline bool isSignalPropertyName(const QString &signalName)
-{
-    // see QmlCompiler::isSignalPropertyName
-    return signalName.size() >= 3 && signalName.startsWith(QLatin1String("on")) &&
-            signalName.at(2).isLetter() && signalName.at(2).isUpper();
-}
-
 static bool hasValidSignal(QObject *object, const QString &propertyName)
 {
-    if (!isSignalPropertyName(propertyName))
+    auto signalName = QQmlSignalNames::handlerNameToSignalName(propertyName);
+    if (!signalName)
         return false;
 
-    QString signalName = propertyName.mid(2);
-    signalName[0] = signalName.at(0).toLower();
-
-    int sigIdx = QQmlPropertyPrivate::findSignalByName(object->metaObject(), signalName.toLatin1()).methodIndex();
+    int sigIdx = QQmlPropertyPrivate::findSignalByName(object->metaObject(), signalName->toLatin1())
+                         .methodIndex();
 
     if (sigIdx == -1)
         return false;
@@ -305,10 +298,8 @@ void QQmlEngineDebugServiceImpl::buildObjectDump(QDataStream &message,
                 if (scope) {
                     const QByteArray methodName = QMetaObjectPrivate::signal(scope->metaObject(),
                                                                              signalHandler->signalIndex()).name();
-                    const QLatin1String methodNameStr(methodName);
-                    if (methodNameStr.size() != 0) {
-                        prop.name = QLatin1String("on") + QChar(methodNameStr.at(0)).toUpper()
-                                + methodNameStr.mid(1);
+                    if (!methodName.isEmpty()) {
+                        prop.name = QQmlSignalNames::signalNameToHandlerName(methodName);
                     }
                 }
             }
diff --git a/src/qml/common/qqmlsignalnames.cpp b/src/qml/common/qqmlsignalnames.cpp
index 5d46531dfb..96c4ee5ad7 100644
--- a/src/qml/common/qqmlsignalnames.cpp
+++ b/src/qml/common/qqmlsignalnames.cpp
@@ -14,10 +14,10 @@ using namespace Qt::Literals;
 static std::optional<qsizetype> firstLetterIdx(QStringView name, qsizetype removePrefix = 0,
                                                qsizetype removeSuffix = 0)
 {
-    auto result = std::find_if(std::next(name.cbegin(), removePrefix),
-                               std::prev(name.cend(), removeSuffix),
+    auto end = std::prev(name.cend(), removeSuffix);
+    auto result = std::find_if(std::next(name.cbegin(), removePrefix), end,
                                [](const QChar &c) { return c.isLetter(); });
-    if (result != name.cend())
+    if (result != end)
         return std::distance(name.begin(), result);
 
     return {};
@@ -157,23 +157,41 @@ QString QQmlSignalNames::signalNameToHandlerName(QAnyStringView signal)
     return handlerName;
 }
 
-/*!
-\internal
-Returns a signal name from \a handlerName string.
-*/
-std::optional<QString> QQmlSignalNames::handlerNameToSignalName(QStringView handler)
+enum HandlerType { ChangedHandler, Handler };
+
+static std::optional<QString> handlerNameToSignalNameHelper(QStringView handler, HandlerType type)
 {
-    if (!isHandlerName(handler))
+    if (!QQmlSignalNames::isHandlerName(handler))
         return {};
 
     QString signalName = handler.sliced(strlen("on")).toString();
     if (signalName.isEmpty())
         return {};
 
-    changeCaseOfFirstLetter(signalName, ToLower);
+    changeCaseOfFirstLetter(signalName, ToLower, 0, type == ChangedHandler ? strlen("Changed") : 0);
     return signalName;
 }
 
+/*!
+\internal
+Returns a signal name from \a handlerName string. Do not use it on changed handlers, see
+changedHandlerNameToSignalName for that!
+*/
+std::optional<QString> QQmlSignalNames::handlerNameToSignalName(QStringView handler)
+{
+    return handlerNameToSignalNameHelper(handler, Handler);
+}
+
+/*!
+\internal
+Returns a signal name from \a changedHandlerName string. Makes sure not to lowercase the 'C' from
+Changed.
+*/
+std::optional<QString> QQmlSignalNames::changedHandlerNameToSignalName(QStringView handler)
+{
+    return handlerNameToSignalNameHelper(handler, ChangedHandler);
+}
+
 bool QQmlSignalNames::isChangedSignalName(QStringView signalName)
 {
     const qsizetype smallestAllowedSize = strlen("XChanged");
diff --git a/src/qml/common/qqmlsignalnames_p.h b/src/qml/common/qqmlsignalnames_p.h
index f777e89812..753f2ca97a 100644
--- a/src/qml/common/qqmlsignalnames_p.h
+++ b/src/qml/common/qqmlsignalnames_p.h
@@ -42,6 +42,7 @@ public:
     static std::optional<QByteArray> changedHandlerNameToPropertyName(QUtf8StringView handler);
 
     static std::optional<QString> handlerNameToSignalName(QStringView handler);
+    static std::optional<QString> changedHandlerNameToSignalName(QStringView changedHandler);
 
     static bool isChangedHandlerName(QStringView signalName);
     static bool isChangedSignalName(QStringView signalName);
diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index 072894adde..2d1a617b09 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -442,38 +442,6 @@ bool IRBuilder::generateFromQml(const QString &code, const QString &url, Documen
     return errors.isEmpty();
 }
 
-bool IRBuilder::isSignalPropertyName(const QString &name)
-{
-    if (name.size() < 3) return false;
-    if (!name.startsWith(QLatin1String("on"))) return false;
-    int ns = name.size();
-    for (int i = 2; i < ns; ++i) {
-        const QChar curr = name.at(i);
-        if (curr.unicode() == '_') continue;
-        if (curr.isUpper()) return true;
-        return false;
-    }
-    return false; // consists solely of underscores - invalid.
-}
-
-QString IRBuilder::signalNameFromSignalPropertyName(const QString &signalPropertyName)
-{
-    Q_ASSERT(signalPropertyName.startsWith(QLatin1String("on")));
-    QString signalNameCandidate = signalPropertyName;
-    signalNameCandidate.remove(0, 2);
-
-    // Note that the property name could start with any alpha or '_' or '$' character,
-    // so we need to do the lower-casing of the first alpha character.
-    for (int firstAlphaIndex = 0; firstAlphaIndex < signalNameCandidate.size(); ++firstAlphaIndex) {
-        if (signalNameCandidate.at(firstAlphaIndex).isUpper()) {
-            signalNameCandidate[firstAlphaIndex] = signalNameCandidate.at(firstAlphaIndex).toLower();
-            return signalNameCandidate;
-        }
-    }
-
-    Q_UNREACHABLE_RETURN(QString());
-}
-
 bool IRBuilder::visit(QQmlJS::AST::UiArrayMemberList *ast)
 {
     return QQmlJS::AST::Visitor::visit(ast);
diff --git a/src/qml/compiler/qqmlirbuilder_p.h b/src/qml/compiler/qqmlirbuilder_p.h
index 5b9c0fce60..2935a3273b 100644
--- a/src/qml/compiler/qqmlirbuilder_p.h
+++ b/src/qml/compiler/qqmlirbuilder_p.h
@@ -506,9 +506,6 @@ public:
     IRBuilder(const QSet<QString> &illegalNames);
     bool generateFromQml(const QString &code, const QString &url, Document *output);
 
-    static bool isSignalPropertyName(const QString &name);
-    static QString signalNameFromSignalPropertyName(const QString &signalPropertyName);
-
     using QQmlJS::AST::Visitor::visit;
     using QQmlJS::AST::Visitor::endVisit;
 
diff --git a/src/qml/qml/qqmlproperty.cpp b/src/qml/qml/qqmlproperty.cpp
index 0e44df219f..7437eefa85 100644
--- a/src/qml/qml/qqmlproperty.cpp
+++ b/src/qml/qml/qqmlproperty.cpp
@@ -20,6 +20,7 @@
 #include <private/qqmlbuiltinfunctions_p.h>
 #include <private/qqmlirbuilder_p.h>
 #include <QtQml/private/qqmllist_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 #include <QStringList>
 #include <QVector>
@@ -363,11 +364,10 @@ void QQmlPropertyPrivate::initProperty(QObject *obj, const QString &name,
     };
 
     QQmlData *ddata = QQmlData::get(currentObject, false);
-    auto findChangeSignal = [&](QStringView signalName) {
-        const QString changed = QStringLiteral("Changed");
-        if (signalName.endsWith(changed)) {
-            const QStringView propName = signalName.first(signalName.size() - changed.size());
-            const QQmlPropertyData *d = ddata->propertyCache->property(propName, currentObject, context);
+    auto findChangeSignal = [&](QStringView changedHandlerName) {
+        if (auto propName = QQmlSignalNames::changedHandlerNameToPropertyName(changedHandlerName)) {
+            const QQmlPropertyData *d =
+                    ddata->propertyCache->property(*propName, currentObject, context);
             while (d && d->isFunction())
                 d = ddata->propertyCache->overrideData(d);
 
@@ -381,19 +381,11 @@ void QQmlPropertyPrivate::initProperty(QObject *obj, const QString &name,
     };
 
     const QString terminalString = terminal.toString();
-    if (QmlIR::IRBuilder::isSignalPropertyName(terminalString)) {
-        QString signalName = terminalString.mid(2);
-        int firstNon_;
-        int length = signalName.size();
-        for (firstNon_ = 0; firstNon_ < length; ++firstNon_)
-            if (signalName.at(firstNon_) != u'_')
-                break;
-        signalName[firstNon_] = signalName.at(firstNon_).toLower();
-
+    if (auto signalName = QQmlSignalNames::handlerNameToSignalName(terminalString)) {
         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
@@ -407,9 +399,9 @@ void QQmlPropertyPrivate::initProperty(QObject *obj, const QString &name,
                 return;
             }
 
-            if (findChangeSignal(signalName))
+            if (findChangeSignal(terminalString))
                 return;
-        } else if (findSignalInMetaObject(signalName.toUtf8())) {
+        } else if (findSignalInMetaObject(signalName->toUtf8())) {
             return;
         }
     }
@@ -744,15 +736,7 @@ QString QQmlProperty::name() const
             d->nameCache = d->core.name(d->object) + QLatin1Char('.') + QString::fromUtf8(vtName);
         } else if (type() & SignalProperty) {
             // ### Qt7: Return the original signal name here. Do not prepend "on"
-            QString name = QStringLiteral("on") + d->core.name(d->object);
-            for (int i = 2, end = name.size(); i != end; ++i) {
-                const QChar c = name.at(i);
-                if (c != u'_') {
-                    name[i] = c.toUpper();
-                    break;
-                }
-            }
-            d->nameCache = name;
+            d->nameCache = QQmlSignalNames::signalNameToHandlerName(d->core.name(d->object));
         } else {
             d->nameCache = d->core.name(d->object);
         }
@@ -1956,9 +1940,8 @@ QMetaMethod QQmlPropertyPrivate::findSignalByName(const QMetaObject *mo, const Q
 
     // If no signal is found, but the signal is of the form "onBlahChanged",
     // return the notify signal for the property "Blah"
-    if (name.endsWith("Changed")) {
-        QByteArray propName = name.mid(0, name.size() - 7);
-        int propIdx = mo->indexOfProperty(propName.constData());
+    if (auto propName = QQmlSignalNames::changedSignalNameToPropertyName(name)) {
+        int propIdx = mo->indexOfProperty(propName->constData());
         if (propIdx >= 0) {
             QMetaProperty prop = mo->property(propIdx);
             if (prop.hasNotifySignal())
diff --git a/src/qml/qml/qqmlpropertycache.cpp b/src/qml/qml/qqmlpropertycache.cpp
index b51fc963f7..d368433949 100644
--- a/src/qml/qml/qqmlpropertycache.cpp
+++ b/src/qml/qml/qqmlpropertycache.cpp
@@ -10,6 +10,7 @@
 #include <private/qmetaobject_p.h>
 #include <private/qmetaobjectbuilder_p.h>
 #include <private/qqmlpropertycachemethodarguments_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 #include <private/qv4value_p.h>
 
@@ -249,8 +250,7 @@ void QQmlPropertyCache::appendSignal(const QString &name, QQmlPropertyData::Flag
     int signalHandlerIndex = signalHandlerIndexCache.size();
     signalHandlerIndexCache.append(handler);
 
-    QString handlerName = QLatin1String("on") + name;
-    handlerName[2] = handlerName.at(2).toUpper();
+    const QString handlerName = QQmlSignalNames::signalNameToHandlerName(name);
 
     setNamedProperty(name, methodIndex + methodOffset(), methodIndexCache.data() + methodIndex);
     setNamedProperty(handlerName, signalHandlerIndex + signalOffset(),
@@ -449,7 +449,7 @@ void QQmlPropertyCache::append(const QMetaObject *metaObject,
             setNamedProperty(methodName, ii, data);
 
             if (data->isSignal()) {
-                QHashedString on(QLatin1String("on") % methodName.at(0).toUpper() % QStringView{methodName}.mid(1));
+                QHashedString on(QQmlSignalNames::signalNameToHandlerName(methodName));
                 setNamedProperty(on, ii, sigdata);
                 ++signalHandlerIndex;
             }
@@ -462,17 +462,8 @@ void QQmlPropertyCache::append(const QMetaObject *metaObject,
             setNamedProperty(methodName, ii, data);
 
             if (data->isSignal()) {
-                int length = methodName.length();
-
-                QVarLengthArray<char, 128> str(length+3);
-                str[0] = 'o';
-                str[1] = 'n';
-                str[2] = QtMiscUtils::toAsciiUpper(rawName[0]);
-                if (length > 1)
-                    memcpy(&str[3], &rawName[1], length - 1);
-                str[length + 2] = '\0';
-
-                QHashedString on(QString::fromLatin1(str.data()));
+                QHashedString on(QQmlSignalNames::signalNameToHandlerName(
+                        QLatin1StringView{ methodName.constData(), methodName.length() }));
                 setNamedProperty(on, ii, data);
                 ++signalHandlerIndex;
             }
diff --git a/src/qml/qml/qqmlpropertycachecreator_p.h b/src/qml/qml/qqmlpropertycachecreator_p.h
index f7d27d113b..a48835f6c1 100644
--- a/src/qml/qml/qqmlpropertycachecreator_p.h
+++ b/src/qml/qml/qqmlpropertycachecreator_p.h
@@ -21,6 +21,7 @@
 #include <private/qqmltypedata_p.h>
 #include <private/inlinecomponentutils_p.h>
 #include <private/qqmlsourcecoordinate_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 #include <QScopedValueRollback>
 #include <vector>
@@ -486,7 +487,8 @@ inline QQmlError QQmlPropertyCacheCreator<ObjectContainer>::createMetaObject(
     for (  ; p != pend; ++p) {
         auto flags = QQmlPropertyData::defaultSignalFlags();
 
-        QString changedSigName = stringAt(p->nameIndex) + QLatin1String("Changed");
+        const QString changedSigName =
+                QQmlSignalNames::propertyNameToChangedSignalName(stringAt(p->nameIndex));
         seenSignals.insert(changedSigName);
 
         cache->appendSignal(changedSigName, flags, effectiveMethodIndex++);
@@ -497,7 +499,8 @@ inline QQmlError QQmlPropertyCacheCreator<ObjectContainer>::createMetaObject(
     for ( ; a != aend; ++a) {
         auto flags = QQmlPropertyData::defaultSignalFlags();
 
-        QString changedSigName = stringAt(a->nameIndex()) + QLatin1String("Changed");
+        const QString changedSigName =
+                QQmlSignalNames::propertyNameToChangedSignalName(stringAt(a->nameIndex()));
         seenSignals.insert(changedSigName);
 
         cache->appendSignal(changedSigName, flags, effectiveMethodIndex++);
diff --git a/src/qml/qml/qqmlpropertyresolver.cpp b/src/qml/qml/qqmlpropertyresolver.cpp
index ff29c38997..0217f7b7b5 100644
--- a/src/qml/qml/qqmlpropertyresolver.cpp
+++ b/src/qml/qml/qqmlpropertyresolver.cpp
@@ -3,6 +3,7 @@
 
 #include "qqmlpropertyresolver_p.h"
 #include <private/qqmlcontextdata_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -43,10 +44,8 @@ const QQmlPropertyData *QQmlPropertyResolver::signal(const QString &name, bool *
         return d;
     }
 
-    if (name.endsWith(QLatin1String("Changed"))) {
-        QString propName = name.mid(0, name.size() - static_cast<int>(strlen("Changed")));
-
-        d = property(propName, notInRevision);
+    if (auto propName = QQmlSignalNames::changedSignalNameToPropertyName(name)) {
+        d = property(*propName, notInRevision);
         if (d)
             return cache->signal(d->notifyIndex());
     }
diff --git a/src/qml/qml/qqmlpropertyvalidator.cpp b/src/qml/qml/qqmlpropertyvalidator.cpp
index b1a61d7e35..23f7516ee4 100644
--- a/src/qml/qml/qqmlpropertyvalidator.cpp
+++ b/src/qml/qml/qqmlpropertyvalidator.cpp
@@ -9,6 +9,7 @@
 #include <private/qqmlpropertycachecreator_p.h>
 #include <private/qqmlpropertyresolver_p.h>
 #include <private/qqmlstringconverters_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 #include <QtCore/qdatetime.h>
 
@@ -140,7 +141,7 @@ QVector<QQmlError> QQmlPropertyValidator::validateObject(
                     customBindings << binding;
                     continue;
                 }
-            } else if (QmlIR::IRBuilder::isSignalPropertyName(name)
+            } else if (QQmlSignalNames::isHandlerName(name)
                        && !(customParser->flags() & QQmlCustomParser::AcceptsSignalHandlers)) {
                 customBindings << binding;
                 continue;
diff --git a/src/qml/qml/qqmltypecompiler.cpp b/src/qml/qml/qqmltypecompiler.cpp
index b921463eb6..85dfb68314 100644
--- a/src/qml/qml/qqmltypecompiler.cpp
+++ b/src/qml/qml/qqmltypecompiler.cpp
@@ -9,6 +9,7 @@
 #include <private/qqmlcomponent_p.h>
 #include <private/qqmlpropertyresolver_p.h>
 #include <private/qqmlcomponentandaliasresolver_p.h>
+#include <private/qqmlsignalnames_p.h>
 
 #define COMPILE_EXCEPTION(token, desc) \
     { \
@@ -325,18 +326,21 @@ bool SignalHandlerResolver::resolveSignalHandlerExpressions(
             continue;
         }
 
-        if (!QmlIR::IRBuilder::isSignalPropertyName(bindingPropertyName))
+        QString qPropertyName;
+        QString signalName;
+        if (auto propertyName =
+                    QQmlSignalNames::changedHandlerNameToPropertyName(bindingPropertyName)) {
+            qPropertyName = *propertyName;
+            signalName = *QQmlSignalNames::changedHandlerNameToSignalName(bindingPropertyName);
+        } else {
+            signalName = QQmlSignalNames::handlerNameToSignalName(bindingPropertyName)
+                                 .value_or(QString());
+        }
+        if (signalName.isEmpty())
             continue;
 
         QQmlPropertyResolver resolver(propertyCache);
 
-        const QString signalName = QmlIR::IRBuilder::signalNameFromSignalPropertyName(
-                    bindingPropertyName);
-
-        QString qPropertyName;
-        if (signalName.endsWith(QLatin1String("Changed")))
-            qPropertyName = signalName.mid(0, signalName.size() - static_cast<int>(strlen("Changed")));
-
         bool notInRevision = false;
         const QQmlPropertyData * const signal = resolver.signal(signalName, &notInRevision);
         const QQmlPropertyData * const signalPropertyData = resolver.property(signalName, /*notInRevision ptr*/nullptr);
@@ -1045,7 +1049,7 @@ bool QQmlDeferredAndCustomParserBindingScanner::scanObject(
                     obj->flags |= Object::HasCustomParserBindings;
                     continue;
                 }
-            } else if (QmlIR::IRBuilder::isSignalPropertyName(name)
+            } else if (QQmlSignalNames::isHandlerName(name)
                        && !(customParser->flags() & QQmlCustomParser::AcceptsSignalHandlers)) {
                 obj->flags |= Object::HasCustomParserBindings;
                 binding->setFlag(Binding::IsCustomParserBinding);
diff --git a/src/qml/types/qqmlconnections.cpp b/src/qml/types/qqmlconnections.cpp
index e69e0087e1..de0c433152 100644
--- a/src/qml/types/qqmlconnections.cpp
+++ b/src/qml/types/qqmlconnections.cpp
@@ -15,6 +15,8 @@
 #include <QtCore/qdebug.h>
 #include <QtCore/qstringlist.h>
 
+#include <QtQml/private/qqmlsignalnames_p.h>
+
 #include <private/qobject_p.h>
 
 QT_BEGIN_NAMESPACE
@@ -205,9 +207,7 @@ void QQmlConnectionsParser::verifyBindings(const QQmlRefPointer<QV4::ExecutableC
         const QV4::CompiledData::Binding *binding = props.at(ii);
         const QString &propName = compilationUnit->stringAt(binding->propertyNameIndex);
 
-        const bool thirdCharacterIsValid = (propName.size() >= 2)
-                && (propName.at(2).isUpper() || propName.at(2) == u'_');
-        if (!propName.startsWith(QLatin1String("on")) || !thirdCharacterIsValid) {
+        if (!QQmlSignalNames::isHandlerName(propName)) {
             error(props.at(ii), QQmlConnections::tr("Cannot assign to non-existent property \"%1\"").arg(propName));
             return;
         }
diff --git a/src/qmlcompiler/qqmljscompiler.cpp b/src/qmlcompiler/qqmljscompiler.cpp
index 9dfe7010b0..2f1bc7a391 100644
--- a/src/qmlcompiler/qqmljscompiler.cpp
+++ b/src/qmlcompiler/qqmljscompiler.cpp
@@ -19,6 +19,8 @@
 #include <QtCore/qfileinfo.h>
 #include <QtCore/qloggingcategory.h>
 
+#include <QtQml/private/qqmlsignalnames_p.h>
+
 #include <limits>
 
 QT_BEGIN_NAMESPACE
@@ -123,9 +125,7 @@ static bool checkArgumentsObjectUseInSignalHandlers(const QmlIR::Document &doc,
             if (binding->type() != QV4::CompiledData::Binding::Type_Script)
                 continue;
             const QString propName =  doc.stringAt(binding->propertyNameIndex);
-            if (!propName.startsWith(QLatin1String("on"))
-                || propName.size() < 3
-                || !propName.at(2).isUpper())
+            if (!QQmlSignalNames::isHandlerName(propName))
                 continue;
             auto compiledFunction = doc.jsModule.functions.value(object->runtimeFunctionIndices.at(binding->value.compiledScriptIndex));
             if (!compiledFunction)
diff --git a/src/qmlcompiler/qqmljsfunctioninitializer.cpp b/src/qmlcompiler/qqmljsfunctioninitializer.cpp
index 9fb83014fe..217b00c52c 100644
--- a/src/qmlcompiler/qqmljsfunctioninitializer.cpp
+++ b/src/qmlcompiler/qqmljsfunctioninitializer.cpp
@@ -8,6 +8,8 @@
 #include <QtCore/qloggingcategory.h>
 #include <QtCore/qfileinfo.h>
 
+#include <QtQml/private/qqmlsignalnames_p.h>
+
 QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
@@ -166,44 +168,45 @@ QQmlJSCompilePass::Function QQmlJSFunctionInitializer::run(
     }
 
     function.isProperty = m_objectType->hasProperty(propertyName);
-    if (!function.isProperty && QmlIR::IRBuilder::isSignalPropertyName(propertyName)) {
-        const QString signalName = QmlIR::IRBuilder::signalNameFromSignalPropertyName(propertyName);
-
-        if (signalName.endsWith(u"Changed"_s)
-                && m_objectType->hasProperty(signalName.chopped(strlen("Changed")))) {
-            function.isSignalHandler = true;
-        } else {
-            const auto methods = m_objectType->methods(signalName);
-            for (const auto &method : methods) {
-                if (method.isCloned())
-                    continue;
-                if (method.methodType() == QQmlJSMetaMethodType::Signal) {
-                    function.isSignalHandler = true;
-                    const auto arguments = method.parameters();
-                    for (qsizetype i = 0, end = arguments.size(); i < end; ++i) {
-                        const auto &type = arguments[i].type();
-                        if (type.isNull()) {
-                            diagnose(u"Cannot resolve the argument type %1."_s.arg(
-                                             arguments[i].typeName()),
-                                     QtDebugMsg, bindingLocation, error);
-                            function.argumentTypes.append(
+    if (!function.isProperty) {
+        if (QQmlSignalNames::isHandlerName(propertyName)) {
+            if (auto actualPropertyName =
+                QQmlSignalNames::changedHandlerNameToPropertyName(propertyName);
+                actualPropertyName && m_objectType->hasProperty(*actualPropertyName)) {
+                function.isSignalHandler = true;
+            } else {
+                auto signalName = QQmlSignalNames::handlerNameToSignalName(propertyName);
+                const auto methods = m_objectType->methods(*signalName);
+                for (const auto &method : methods) {
+                    if (method.isCloned())
+                        continue;
+                    if (method.methodType() == QQmlJSMetaMethodType::Signal) {
+                        function.isSignalHandler = true;
+                        const auto arguments = method.parameters();
+                        for (qsizetype i = 0, end = arguments.size(); i < end; ++i) {
+                            const auto &type = arguments[i].type();
+                            if (type.isNull()) {
+                                diagnose(u"Cannot resolve the argument type %1."_s.arg(
+                                                 arguments[i].typeName()),
+                                         QtDebugMsg, bindingLocation, error);
+                                function.argumentTypes.append(
                                         m_typeResolver->tracked(
-                                            m_typeResolver->globalType(m_typeResolver->varType())));
-                        } else {
-                            function.argumentTypes.append(m_typeResolver->tracked(
-                                                              m_typeResolver->globalType(type)));
+                                                m_typeResolver->globalType(m_typeResolver->varType())));
+                            } else {
+                                function.argumentTypes.append(m_typeResolver->tracked(
+                                        m_typeResolver->globalType(type)));
+                            }
                         }
+                        break;
                     }
-                    break;
+                }
+                if (!function.isSignalHandler) {
+                    diagnose(u"Could not compile signal handler for %1: The signal does not exist"_s.arg(
+                                     *signalName),
+                             QtWarningMsg, bindingLocation, error);
                 }
             }
         }
-
-        if (!function.isSignalHandler) {
-            diagnose(u"Could not compile signal handler for %1: The signal does not exist"_s.arg(
-                         signalName),
-                     QtWarningMsg, bindingLocation, error);
-        }
     }
 
     if (!function.isSignalHandler) {
diff --git a/src/qmlcompiler/qqmljsimportvisitor.cpp b/src/qmlcompiler/qqmljsimportvisitor.cpp
index a772f1b5a2..181607d42e 100644
--- a/src/qmlcompiler/qqmljsimportvisitor.cpp
+++ b/src/qmlcompiler/qqmljsimportvisitor.cpp
@@ -13,6 +13,7 @@
 #include <QtCore/qrect.h>
 #include <QtCore/qsize.h>
 
+#include <QtQml/private/qqmlsignalnames_p.h>
 #include <QtQml/private/qv4codegen_p.h>
 #include <QtQml/private/qqmlstringconverters_p.h>
 #include <QtQml/private/qqmlirbuilder_p.h>
@@ -963,7 +964,7 @@ void QQmlJSImportVisitor::checkSignal(
         const QQmlJSScope::ConstPtr &signalScope, const QQmlJS::SourceLocation &location,
         const QString &handlerName, const QStringList &handlerParameters)
 {
-    const auto signal = QQmlJSUtils::signalName(handlerName);
+    const auto signal = QQmlSignalNames::handlerNameToSignalName(handlerName);
 
     std::optional<QQmlJSMetaMethod> signalMethod;
     const auto setSignalMethod = [&](const QQmlJSScope::ConstPtr &scope, const QString &name) {
@@ -975,8 +976,7 @@ void QQmlJSImportVisitor::checkSignal(
     if (signal.has_value()) {
         if (signalScope->hasMethod(*signal)) {
             setSignalMethod(signalScope, *signal);
-        } else if (auto p = QQmlJSUtils::changeHandlerProperty(signalScope, *signal);
-                   p.has_value()) {
+        } else if (auto p = QQmlJSUtils::propertyFromChangedHandler(signalScope, handlerName)) {
             // we have a change handler of the form "onXChanged" where 'X'
             // is a property name
 
@@ -2025,11 +2025,11 @@ bool QQmlJSImportVisitor::visit(UiScriptBinding *scriptBinding)
         prefix.clear();
     }
 
-    auto name = group->name.toString();
+    const auto name = group->name.toString();
 
     // This is a preliminary check.
     // Even if the name starts with "on", it might later turn out not to be a signal.
-    const auto signal = QQmlJSUtils::signalName(name);
+    const auto signal = QQmlSignalNames::handlerNameToSignalName(name);
 
     if (!signal.has_value() || m_currentScope->hasProperty(name)) {
         m_propertyBindings[m_currentScope].append(
@@ -2079,7 +2079,7 @@ bool QQmlJSImportVisitor::visit(UiScriptBinding *scriptBinding)
             if (!methods.isEmpty()) {
                 kind = QQmlSA::ScriptBindingKind::Script_SignalHandler;
                 checkSignal(scope, groupLocation, name, signalParameters);
-            } else if (QQmlJSUtils::changeHandlerProperty(scope, signalName).has_value()) {
+            } else if (QQmlJSUtils::propertyFromChangedHandler(scope, name).has_value()) {
                 kind = QQmlSA::ScriptBindingKind::Script_ChangeHandler;
                 checkSignal(scope, groupLocation, name, signalParameters);
             } else if (scope->hasProperty(name)) {
diff --git a/src/qmlcompiler/qqmljsscope.cpp b/src/qmlcompiler/qqmljsscope.cpp
index 8e5e66675a..4664e62c54 100644
--- a/src/qmlcompiler/qqmljsscope.cpp
+++ b/src/qmlcompiler/qqmljsscope.cpp
@@ -81,7 +81,8 @@ void QQmlJSScope::insertJSIdentifier(const QString &name, const JavaScriptIdenti
 void QQmlJSScope::insertPropertyIdentifier(const QQmlJSMetaProperty &property)
 {
     addOwnProperty(property);
-    QQmlJSMetaMethod method(property.propertyName() + u"Changed"_s, u"void"_s);
+    QQmlJSMetaMethod method(
+            QQmlSignalNames::propertyNameToChangedSignalName(property.propertyName()), u"void"_s);
     method.setMethodType(QQmlJSMetaMethodType::Signal);
     method.setIsImplicitQmlPropertyChangeSignal(true);
     addOwnMethod(method);
diff --git a/src/qmlcompiler/qqmljsutils_p.h b/src/qmlcompiler/qqmljsutils_p.h
index 5e4f6004f8..87e75e5cfa 100644
--- a/src/qmlcompiler/qqmljsutils_p.h
+++ b/src/qmlcompiler/qqmljsutils_p.h
@@ -25,6 +25,7 @@
 #include <QtCore/qstring.h>
 #include <QtCore/qstringview.h>
 #include <QtCore/qstringbuilder.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 #include <private/qduplicatetracker_p.h>
 
 #include <optional>
@@ -99,26 +100,6 @@ struct Q_QMLCOMPILER_PRIVATE_EXPORT QQmlJSUtils
         return type;
     }
 
-    /*! \internal
-        Returns a signal name from \a handlerName string.
-    */
-    static std::optional<QString> signalName(QStringView handlerName)
-    {
-        if (handlerName.startsWith(u"on") && handlerName.size() > 2) {
-            QString signal = handlerName.mid(2).toString();
-            for (int i = 0; i < signal.size(); ++i) {
-                QChar &ch = signal[i];
-                if (ch.isLower())
-                    return {};
-                if (ch.isUpper()) {
-                    ch = ch.toLower();
-                    return signal;
-                }
-            }
-        }
-        return {};
-    }
-
     static std::optional<QQmlJSMetaProperty>
     changeHandlerProperty(const QQmlJSScope::ConstPtr &scope, QStringView signalName)
     {
@@ -134,6 +115,21 @@ struct Q_QMLCOMPILER_PRIVATE_EXPORT QQmlJSUtils
         return {};
     }
 
+    static std::optional<QQmlJSMetaProperty>
+    propertyFromChangedHandler(const QQmlJSScope::ConstPtr &scope, QStringView changedHandler)
+    {
+        auto signalName = QQmlSignalNames::changedHandlerNameToPropertyName(changedHandler);
+        if (!signalName)
+            return {};
+
+        auto p = scope->property(*signalName);
+        const bool isBindable = !p.bindable().isEmpty();
+        const bool canNotify = !p.notify().isEmpty();
+        if (p.isValid() && (isBindable || canNotify))
+            return p;
+        return {};
+    }
+
     static bool hasCompositeBase(const QQmlJSScope::ConstPtr &scope)
     {
         if (!scope)
diff --git a/src/qmldom/qqmldomelements_p.h b/src/qmldom/qqmldomelements_p.h
index 4cc1cd016e..a26b624a1b 100644
--- a/src/qmldom/qqmldomelements_p.h
+++ b/src/qmldom/qqmldomelements_p.h
@@ -22,6 +22,7 @@
 
 #include <QtQml/private/qqmljsast_p.h>
 #include <QtQml/private/qqmljsengine_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 #include <QtCore/QCborValue>
 #include <QtCore/QCborMap>
@@ -554,9 +555,7 @@ public:
     bool isSignalHandler() const
     {
         QString baseName = m_name.split(QLatin1Char('.')).last();
-        if (baseName.startsWith(u"on") && baseName.size() > 2 && baseName.at(2).isUpper())
-            return true;
-        return false;
+        return QQmlSignalNames::isHandlerName(baseName);
     }
     static QString preCodeForName(QStringView n)
     {
diff --git a/src/qmlls/qqmlcompletionsupport.cpp b/src/qmlls/qqmlcompletionsupport.cpp
index 2545e4abc0..93b4a472df 100644
--- a/src/qmlls/qqmlcompletionsupport.cpp
+++ b/src/qmlls/qqmlcompletionsupport.cpp
@@ -10,6 +10,7 @@
 #include <QtCore/QRegularExpression>
 #include <QtQmlDom/private/qqmldomexternalitems_p.h>
 #include <QtQmlDom/private/qqmldomtop_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 QT_BEGIN_NAMESPACE
 using namespace QLspSpecification;
@@ -287,8 +288,7 @@ static QList<CompletionItem> bindingsCompletions(DomItem &containingObject)
                         if (it.value().methodType == MethodInfo::MethodType::Signal) {
                             CompletionItem comp;
                             QString signal = it.key();
-                            comp.label =
-                                    (u"on"_s + signal.at(0).toUpper() + signal.mid(1)).toUtf8();
+                            comp.label = QQmlSignalNames::signalNameToHandlerName(signal).toUtf8();
                             res.append(comp);
                         }
                         ++it;
diff --git a/src/quick/util/qquickpropertychanges.cpp b/src/quick/util/qquickpropertychanges.cpp
index fcb6e71e17..f1c01e3a0b 100644
--- a/src/quick/util/qquickpropertychanges.cpp
+++ b/src/quick/util/qquickpropertychanges.cpp
@@ -20,6 +20,7 @@
 #include <private/qqmlirbuilder_p.h>
 
 #include <QtCore/qdebug.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 #include <private/qobject_p.h>
 
@@ -267,7 +268,7 @@ void QQuickPropertyChangesPrivate::decodeBinding(const QString &propertyPrefix,
         break;
     }
 
-    if (binding->isSignalHandler() || QmlIR::IRBuilder::isSignalPropertyName(propertyName)) {
+    if (binding->isSignalHandler() || QQmlSignalNames::isHandlerName(propertyName)) {
         QQmlProperty prop = property(propertyName);
         if (prop.isSignalProperty()) {
             QQuickReplaceSignalHandler *handler = new QQuickReplaceSignalHandler;
diff --git a/tests/auto/qml/common/tst_qml_common.cpp b/tests/auto/qml/common/tst_qml_common.cpp
index 67d72500e0..13d7ac0f72 100644
--- a/tests/auto/qml/common/tst_qml_common.cpp
+++ b/tests/auto/qml/common/tst_qml_common.cpp
@@ -37,6 +37,8 @@ void tst_qml_common::tst_propertyNameToChangedHandlerName_data()
     QTest::addRow("___123aProperty") << u"___123a"_s << u"on___123AChanged"_s;
     QTest::addRow("___123Property") << u"___123"_s << u"on___123Changed"_s;
     QTest::addRow("AProperty") << u"A"_s << u"onAChanged"_s;
+    QTest::addRow("_Property") << u"_"_s << u"on_Changed"_s;
+    QTest::addRow("$Property") << u"$"_s << u"on$Changed"_s;
 }
 void tst_qml_common::tst_propertyNameToChangedHandlerName()
 {
@@ -67,6 +69,8 @@ void tst_qml_common::tst_signalNameToHandlerName_data()
     QTest::addRow("___123aProperty") << u"___123a"_s << u"on___123A"_s;
     QTest::addRow("___123Property") << u"___123"_s << u"on___123"_s;
     QTest::addRow("AProperty") << u"A"_s << u"onA"_s;
+    QTest::addRow("_Property") << u"_"_s << u"on_"_s;
+    QTest::addRow("$Property") << u"$"_s << u"on$"_s;
 }
 
 void tst_qml_common::tst_signalNameToHandlerName()
@@ -150,6 +154,8 @@ void tst_qml_common::tst_isChangedHandlerName_data()
     QTest::addRow("empty") << u""_s << false;
     QTest::addRow("empty2") << u"onChanged"_s << false;
     QTest::addRow("on") << u"on"_s << false;
+    QTest::addRow("on_Changed") << u"on_Changed"_s << true;
+    QTest::addRow("on$Changed") << u"on$Changed"_s << true;
 }
 void tst_qml_common::tst_isChangedHandlerName()
 {
diff --git a/tests/auto/qml/debugger/qqmlenginedebugservice/tst_qqmlenginedebugservice.cpp b/tests/auto/qml/debugger/qqmlenginedebugservice/tst_qqmlenginedebugservice.cpp
index 97507f2512..586ed8ea8e 100644
--- a/tests/auto/qml/debugger/qqmlenginedebugservice/tst_qqmlenginedebugservice.cpp
+++ b/tests/auto/qml/debugger/qqmlenginedebugservice/tst_qqmlenginedebugservice.cpp
@@ -22,6 +22,7 @@
 #include <QtQml/qqmlproperty.h>
 #include <QtQml/qqmlincubator.h>
 #include <QtQml/qqmlapplicationengine.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 #include <QtQuick/qquickitem.h>
 
 #include <QtNetwork/qhostaddress.h>
@@ -244,7 +245,7 @@ void tst_QQmlEngineDebugService::recursiveObjectTest(
         QCOMPARE(p.objectDebugId, QQmlDebugService::idForObject(o));
 
         // signal properties are fake - they are generated from QQmlAbstractBoundSignal children
-        if (p.name.startsWith("on") && p.name.size() > 2 && p.name[2].isUpper()) {
+        if (QQmlSignalNames::isHandlerName(p.name)) {
             QString signal = p.value.toString();
             QQmlBoundSignalExpression *expr = QQmlPropertyPrivate::signalExpression(QQmlProperty(o, p.name));
             QVERIFY(expr && expr->expression() == signal);
diff --git a/tests/auto/qml/qmlcppcodegen/data/conversions2.qml b/tests/auto/qml/qmlcppcodegen/data/conversions2.qml
index c3a9414ae2..d0d1fc9b8f 100644
--- a/tests/auto/qml/qmlcppcodegen/data/conversions2.qml
+++ b/tests/auto/qml/qmlcppcodegen/data/conversions2.qml
@@ -94,6 +94,8 @@ Item {
     }
 
     function qtest_signalHandlerName(sn) {
+        // Warning: to not test for signal handlers like this in actual code.
+        // Use the helper methods in QQmlSignalNames instead.
         if (sn.substr(0, 2) === "on" && sn[2] === sn[2].toUpperCase())
             return sn
         return "on" + sn.substr(0, 1).toUpperCase() + sn.substr(1)
diff --git a/tests/auto/qml/qmlcppcodegen/data/methods.qml b/tests/auto/qml/qmlcppcodegen/data/methods.qml
index 3abd14c9c1..c045c2249b 100644
--- a/tests/auto/qml/qmlcppcodegen/data/methods.qml
+++ b/tests/auto/qml/qmlcppcodegen/data/methods.qml
@@ -35,6 +35,8 @@ BirthdayParty {
     }
 
     function stuff(sn) {
+        // Warning: to not test for signal handlers like this in actual code.
+        // Use the helper methods in QQmlSignalNames instead.
         if (sn.substr(0, 2) === "on" && sn[2] === sn[2].toUpperCase())
             return sn
         return "on" + sn.substr(0, 1).toUpperCase() + sn.substr(1)
diff --git a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.3.qml b/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.3.qml
deleted file mode 100644
index d611e0fe30..0000000000
--- a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.3.qml
+++ /dev/null
@@ -1,12 +0,0 @@
-import QtQuick 2.0
-
-Item {
-    property int changeCount: 0
-
-    // invalid property name - we don't allow $
-    property bool $nameWithDollarsign: false
-
-    on$NameWithDollarsignChanged: {
-        changeCount = changeCount + 4;
-    }
-}
diff --git a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.4.qml b/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.4.qml
deleted file mode 100644
index a6862517c6..0000000000
--- a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlotErrors.4.qml
+++ /dev/null
@@ -1,12 +0,0 @@
-import QtQuick 2.0
-
-Item {
-    property int changeCount: 0
-
-    property bool _6nameWithUnderscoreNumber: false
-
-    // invalid property name - the first character after an underscore must be a letter
-    on_6NameWithUnderscoreNumberChanged: {
-        changeCount = changeCount + 3;
-    }
-}
diff --git a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlots.qml b/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlots.qml
index f91fb71f1f..9a3141e15a 100644
--- a/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlots.qml
+++ b/tests/auto/qml/qqmlecmascript/data/changeslots/propertyChangeSlots.qml
@@ -6,6 +6,8 @@ Item {
     property bool normalName: false
     property bool _nameWithUnderscore: false
     property bool ____nameWithUnderscores: false
+    property bool _6nameWithUnderscoreNumber: false
+    property bool $nameWithDollarsign: false
 
     onNormalNameChanged: {
         changeCount = changeCount + 1;
@@ -19,9 +21,20 @@ Item {
         changeCount = changeCount + 3;
     }
 
+    on$NameWithDollarsignChanged: {
+        changeCount = changeCount + 4;
+    }
+
+    on_6NameWithUnderscoreNumberChanged: {
+        changeCount = changeCount + 5;
+    }
+
     Component.onCompleted: {
         normalName = true;
         _nameWithUnderscore = true;
         ____nameWithUnderscores = true;
+        $nameWithDollarsign = true;
+        _6nameWithUnderscoreNumber = true;
     }
+
 }
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 69a342bcb9..ca578e1f83 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -5300,6 +5300,7 @@ void tst_qqmlecmascript::propertyChangeSlots()
     QQmlComponent component(&engine, testFileUrl("changeslots/propertyChangeSlots.qml"));
     QScopedPointer<QObject> object(component.create());
     QVERIFY2(object, qPrintable(component.errorString()));
+    QCOMPARE(object->property("changeCount"), 15);
 
     // ensure that invalid property names fail properly.
     QTest::ignoreMessage(QtWarningMsg, "QQmlComponent: Component is not ready");
@@ -5315,20 +5316,6 @@ void tst_qqmlecmascript::propertyChangeSlots()
     QCOMPARE(e2.errors().at(0).toString(), expectedErrorString);
     object.reset(e2.create());
     QVERIFY(!object);
-
-    QTest::ignoreMessage(QtWarningMsg, "QQmlComponent: Component is not ready");
-    QQmlComponent e3(&engine, testFileUrl("changeslots/propertyChangeSlotErrors.3.qml"));
-    expectedErrorString = e3.url().toString() + QLatin1String(":9:5: Cannot assign to non-existent property \"on$NameWithDollarsignChanged\"");
-    QCOMPARE(e3.errors().at(0).toString(), expectedErrorString);
-    object.reset(e3.create());
-    QVERIFY(!object);
-
-    QTest::ignoreMessage(QtWarningMsg, "QQmlComponent: Component is not ready");
-    QQmlComponent e4(&engine, testFileUrl("changeslots/propertyChangeSlotErrors.4.qml"));
-    expectedErrorString = e4.url().toString() + QLatin1String(":9:5: Cannot assign to non-existent property \"on_6NameWithUnderscoreNumberChanged\"");
-    QCOMPARE(e4.errors().at(0).toString(), expectedErrorString);
-    object.reset(e4.create());
-    QVERIFY(!object);
 }
 
 void tst_qqmlecmascript::propertyVar_data()
diff --git a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
index 462082ed03..fbc09f35e0 100644
--- a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
+++ b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
@@ -422,6 +422,10 @@ private slots:
 
     void attachedInCtor();
     void byteArrayConversion();
+    void propertySignalNames_data();
+    void propertySignalNames();
+    void signalNames_data();
+    void signalNames();
 
 private:
     QQmlEngine engine;
@@ -8140,6 +8144,99 @@ void tst_qqmllanguage::byteArrayConversion()
     QCOMPARE(receiver->byteArrays[0], QByteArray("\1\2\3"));
     QCOMPARE(receiver->byteArrays[1], QByteArray("\4\5\6"));
 }
+void tst_qqmllanguage::propertySignalNames_data()
+{
+    QTest::addColumn<QString>("propertyName");
+    QTest::addColumn<QString>("propertyChangedSignal");
+    QTest::addColumn<QString>("propertyChangedHandler");
+    QTest::addRow("helloWorld") << u"helloWorld"_s << u"helloWorldChanged"_s
+                                << u"onHelloWorldChanged"_s;
+    QTest::addRow("$helloWorld") << u"$helloWorld"_s << u"$helloWorldChanged"_s
+                                 << u"on$HelloWorldChanged"_s;
+    QTest::addRow("_helloWorld") << u"_helloWorld"_s << u"_helloWorldChanged"_s
+                                 << u"on_HelloWorldChanged"_s;
+    QTest::addRow("_") << u"_"_s << u"_Changed"_s << u"on_Changed"_s;
+    QTest::addRow("$") << u"$"_s << u"$Changed"_s << u"on$Changed"_s;
+    QTest::addRow("ä") << u"ä"_s << u"äChanged"_s << u"onÄChanged"_s;
+    QTest::addRow("___123a") << u"___123a"_s << u"___123aChanged"_s << u"on___123AChanged"_s;
+}
+void tst_qqmllanguage::propertySignalNames()
+{
+    QFETCH(QString, propertyName);
+    QFETCH(QString, propertyChangedSignal);
+    QFETCH(QString, propertyChangedHandler);
+    QQmlEngine e;
+    QQmlComponent c(&e);
+    c.setData(uR"(
+import QtQuick
+Item {
+    property int %1: 456
+    property bool success: false
+    function f() { %1 = 123; }
+    function g() { %2(); }
+    %3: success = true
+})"_s.arg(propertyName, propertyChangedSignal, propertyChangedHandler)
+                      .toUtf8(),
+              QUrl());
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(o != nullptr);
+    const QMetaObject *metaObject = o->metaObject();
+    auto signalIndex =
+            metaObject->indexOfSignal(propertyChangedSignal.append("()").toStdString().c_str());
+    QVERIFY(signalIndex > -1);
+    auto signal = metaObject->method(signalIndex);
+    QVERIFY(signal.isValid());
+    QSignalSpy changeSignal(o.data(), signal);
+    QMetaObject::invokeMethod(o.data(), "f");
+    QCOMPARE(o->property(propertyName.toStdString().c_str()), 123);
+    QVERIFY(changeSignal.size() == 1);
+    QCOMPARE(o->property("success"), true);
+    QMetaObject::invokeMethod(o.data(), "g");
+    QVERIFY(changeSignal.size() == 2);
+}
+void tst_qqmllanguage::signalNames_data()
+{
+    QTest::addColumn<QString>("signalName");
+    QTest::addColumn<QString>("handlerName");
+    QTest::addRow("helloWorld") << u"helloWorld"_s << u"onHelloWorld"_s;
+    QTest::addRow("$helloWorld") << u"$helloWorld"_s << u"on$HelloWorld"_s;
+    QTest::addRow("_helloWorld") << u"_helloWorld"_s << u"on_HelloWorld"_s;
+    QTest::addRow("_") << u"_"_s << u"on_"_s;
+    QTest::addRow("aUmlaut") << u"ä"_s << u"onÄ"_s;
+    QTest::addRow("___123a") << u"___123a"_s << u"on___123A"_s;
+}
+void tst_qqmllanguage::signalNames()
+{
+    QFETCH(QString, signalName);
+    QFETCH(QString, handlerName);
+    QQmlEngine e;
+    QQmlComponent c(&e);
+    c.setData(uR"(
+import QtQuick
+Item {
+    signal %1()
+    property bool success: false
+    function f() { %1(); }
+    %2: success = true
+})"_s.arg(signalName, handlerName)
+                      .toUtf8(),
+              QUrl());
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(o != nullptr);
+    const QMetaObject *metaObject = o->metaObject();
+    auto signalIndex = metaObject->indexOfSignal(signalName.append("()").toStdString().c_str());
+    QVERIFY(signalIndex > -1);
+    auto signal = metaObject->method(signalIndex);
+    QVERIFY(signal.isValid());
+    QSignalSpy changeSignal(o.data(), signal);
+    signal.invoke(o.data());
+    QVERIFY(changeSignal.size() == 1);
+    QCOMPARE(o->property("success"), true);
+    QMetaObject::invokeMethod(o.data(), "f");
+    QVERIFY(changeSignal.size() == 2);
+}
 
 QTEST_MAIN(tst_qqmllanguage)
 
diff --git a/tests/auto/qml/qqmllistmodel/tst_qqmllistmodel.cpp b/tests/auto/qml/qqmllistmodel/tst_qqmllistmodel.cpp
index a84ffb87b4..8df8e12dc7 100644
--- a/tests/auto/qml/qqmllistmodel/tst_qqmllistmodel.cpp
+++ b/tests/auto/qml/qqmllistmodel/tst_qqmllistmodel.cpp
@@ -8,6 +8,7 @@
 #include <QtQml/private/qqmlengine_p.h>
 #include <QtQmlModels/private/qqmllistmodel_p.h>
 #include <QtQml/private/qqmlexpression_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 #include <QQmlComponent>
 
 #include <QtCore/qtimer.h>
@@ -1098,12 +1099,12 @@ void tst_qqmllistmodel::property_changes()
     expr.evaluate();
     QVERIFY2(!expr.hasError(), qPrintable(expr.error().toString()));
 
-    QString signalHandler = "on" + QString(roleName[0].toUpper()) + roleName.mid(1, roleName.size()) + "Changed:";
+    QString signalHandler = QQmlSignalNames::propertyNameToChangedHandlerName(roleName);
     QString qml = "import QtQuick 2.0\n"
                   "Connections {\n"
                         "property bool gotSignal: false\n"
                         "target: model.get(" + QString::number(listIndex) + ")\n"
-                        + signalHandler + " gotSignal = true\n"
+                        + signalHandler + ": gotSignal = true\n"
                   "}\n";
 
     QQmlComponent component(&engine);
diff --git a/tools/qmlplugindump/main.cpp b/tools/qmlplugindump/main.cpp
index 42b9544b04..4031bf91d9 100644
--- a/tools/qmlplugindump/main.cpp
+++ b/tools/qmlplugindump/main.cpp
@@ -30,6 +30,7 @@
 #include <QtCore/private/qobject_p.h>
 #include <QtCore/private/qmetaobject_p.h>
 #include <QtQmlTypeRegistrar/private/qqmljsstreamwriter_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 #include <QRegularExpression>
 #include <iostream>
@@ -690,10 +691,13 @@ private:
         for (int index = meta->propertyOffset(); index < meta->propertyCount(); ++index) {
             const QMetaProperty &property = meta->property(index);
             dump(property, metaRevision, knownAttributes);
+            const QByteArray changedSignalName =
+                    QQmlSignalNames::propertyNameToChangedSignalName(property.name());
             if (knownAttributes)
-                knownAttributes->knownMethod(QByteArray(property.name()).append("Changed"),
-                                             0, QTypeRevision::fromEncodedVersion(property.revision()));
-            implicitSignals.insert(QString("%1Changed").arg(QString::fromUtf8(property.name())));
+                knownAttributes->knownMethod(
+                        changedSignalName, 0,
+                        QTypeRevision::fromEncodedVersion(property.revision()));
+            implicitSignals.insert(changedSignalName);
         }
         return implicitSignals;
     }
diff --git a/tools/qmltc/qmltccompiler.cpp b/tools/qmltc/qmltccompiler.cpp
index 34077a29d8..6bdbdcf25d 100644
--- a/tools/qmltc/qmltccompiler.cpp
+++ b/tools/qmltc/qmltccompiler.cpp
@@ -8,6 +8,7 @@
 #include "qmltccompilerpieces.h"
 
 #include <QtCore/qloggingcategory.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 #include <private/qqmljsutils_p.h>
 
 #include <algorithm>
@@ -1734,7 +1735,7 @@ void QmltcCompiler::compileScriptBinding(QmltcType &current,
         break;
     }
     case QQmlSA::ScriptBindingKind::Script_SignalHandler: {
-        const auto name = QQmlJSUtils::signalName(propertyName);
+        const auto name = QQmlSignalNames::handlerNameToSignalName(propertyName);
         Q_ASSERT(name.has_value());
         compileScriptSignal(*name);
         break;
@@ -1743,9 +1744,10 @@ void QmltcCompiler::compileScriptBinding(QmltcType &current,
         const QString objectClassName = objectType->internalName();
         const QString bindingFunctorName = newSymbol(bindingSymbolName + u"Functor");
 
-        const auto signalName = QQmlJSUtils::signalName(propertyName);
+        const auto signalName = QQmlSignalNames::handlerNameToSignalName(propertyName);
         Q_ASSERT(signalName.has_value()); // an error somewhere else
-        const auto actualProperty = QQmlJSUtils::changeHandlerProperty(objectType, *signalName);
+        const auto actualProperty =
+                QQmlJSUtils::propertyFromChangedHandler(objectType, propertyName);
         Q_ASSERT(actualProperty.has_value()); // an error somewhere else
         const auto actualPropertyType = actualProperty->type();
         if (!actualPropertyType) {
diff --git a/tools/qmltc/qmltcpropertyutils.h b/tools/qmltc/qmltcpropertyutils.h
index db26c498dd..8a69e5ef09 100644
--- a/tools/qmltc/qmltcpropertyutils.h
+++ b/tools/qmltc/qmltcpropertyutils.h
@@ -6,6 +6,7 @@
 
 #include <private/qqmljsmetatypes_p.h>
 #include <private/qqmljsscope_p.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -35,13 +36,11 @@ struct QmltcPropertyData
 
     QmltcPropertyData(const QString &propertyName)
     {
-        const QString nameWithUppercase = propertyName[0].toUpper() + propertyName.sliced(1);
-
         read = propertyName;
-        write = u"set" + nameWithUppercase;
-        bindable = u"bindable" + nameWithUppercase;
-        notify = propertyName + u"Changed";
-        reset = u"reset" + nameWithUppercase;
+        write = QQmlSignalNames::addPrefixToPropertyName(u"set", propertyName);
+        bindable = QQmlSignalNames::addPrefixToPropertyName(u"bindable", propertyName);
+        notify = QQmlSignalNames::propertyNameToChangedSignalName(propertyName);
+        reset = QQmlSignalNames::addPrefixToPropertyName(u"reset", propertyName);
     }
 
     QString read;
diff --git a/tools/qmltc/qmltcvisitor.cpp b/tools/qmltc/qmltcvisitor.cpp
index 3acee13bbb..b15c9cdae8 100644
--- a/tools/qmltc/qmltcvisitor.cpp
+++ b/tools/qmltc/qmltcvisitor.cpp
@@ -8,6 +8,7 @@
 #include <QtCore/qstack.h>
 #include <QtCore/qdir.h>
 #include <QtCore/qloggingcategory.h>
+#include <QtQml/private/qqmlsignalnames_p.h>
 
 #include <private/qqmljsutils_p.h>
 
@@ -269,7 +270,7 @@ bool QmltcVisitor::visit(QQmlJS::AST::UiPublicMember *publicMember)
             owner->addOwnProperty(property);
         }
 
-        const QString notifyName = name + u"Changed"_s;
+        const QString notifyName = QQmlSignalNames::propertyNameToChangedSignalName(name);
         // also check that notify is already a method of the scope
         {
             auto owningScope = m_savedBindingOuterScope ? m_savedBindingOuterScope : m_currentScope;