moc/QMetaProperty: Remove limitation on non-own-class notify signals

The moc generated code does a sanity check that NOTIFY signals actually
exist in the parent class when they cannot be found in the class moc
currently runs on.
The logic there was however too simplistic, and couldn't deal with
signals taking a parameter.
Fix this, and take the opportunity to use a proper static_assert instead
of generating a "normal" compile error.

We do not do any checks for the presence of QPrivateSignal, as the whole
point of QPrivateSignal is that it should be private (and not e.g.
protected).

Moreover, we adjust QMetaProperty::notifySignalIndex to take
single-argument notify methods into consideration as well when
encontering an unresolved notify index.

Fixes: QTBUG-115989
Pick-to: 6.7
Change-Id: I8a056a15777f3132691e207b4b9ab6c2c9b2126d
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

5 files changed, 86 insertions, 21 deletions

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index 3d0eeb1683..d45673ef25 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -3973,20 +3973,23 @@ int QMetaProperty::notifySignalIndex() const
     if (!mobj || data.notifyIndex() == std::numeric_limits<uint>::max())
         return -1;
     uint methodIndex = data.notifyIndex();
-    if (methodIndex & IsUnresolvedSignal) {
-        methodIndex &= ~IsUnresolvedSignal;
-        const QByteArray signalName = stringData(mobj, methodIndex);
-        const QMetaObject *m = mobj;
-        const int idx = QMetaObjectPrivate::indexOfMethodRelative<MethodSignal>(&m, signalName, 0, nullptr);
-        if (idx >= 0) {
-            return idx + m->methodOffset();
-        } else {
-            qWarning("QMetaProperty::notifySignal: cannot find the NOTIFY signal %s in class %s for property '%s'",
-                     signalName.constData(), mobj->className(), name());
-            return -1;
-        }
-    }
-    return methodIndex + mobj->methodOffset();
+    if (!(methodIndex & IsUnresolvedSignal))
+        return methodIndex + mobj->methodOffset();
+    methodIndex &= ~IsUnresolvedSignal;
+    const QByteArray signalName = stringData(mobj, methodIndex);
+    const QMetaObject *m = mobj;
+    // try 0-arg signal
+    int idx = QMetaObjectPrivate::indexOfMethodRelative<MethodSignal>(&m, signalName, 0, nullptr);
+    if (idx >= 0)
+        return idx + m->methodOffset();
+    // try 1-arg signal
+    QArgumentType argType(typeId());
+    idx = QMetaObjectPrivate::indexOfMethodRelative<MethodSignal>(&m, signalName, 1, &argType);
+    if (idx >= 0)
+        return idx + m->methodOffset();
+    qWarning("QMetaProperty::notifySignal: cannot find the NOTIFY signal %s in class %s for property '%s'",
+             signalName.constData(), mobj->className(), name());
+    return -1;
 }
 
 // This method has been around for a while, but the documentation was marked \internal until 5.1
diff --git a/src/tools/moc/generator.cpp b/src/tools/moc/generator.cpp
index 967d7236de..02e9ef178a 100644
--- a/src/tools/moc/generator.cpp
+++ b/src/tools/moc/generator.cpp
@@ -637,12 +637,29 @@ void Generator::generateCode()
 // Generate function to make sure the non-class signals exist in the parent classes
 //
     if (!cdef->nonClassSignalList.isEmpty()) {
-        fprintf(out, "// If you get a compile error in this function it can be because either\n");
-        fprintf(out, "//     a) You are using a NOTIFY signal that does not exist. Fix it.\n");
-        fprintf(out, "//     b) You are using a NOTIFY signal that does exist (in a parent class) but has a non-empty parameter list. This is a moc limitation.\n");
-        fprintf(out, "[[maybe_unused]] static void checkNotifySignalValidity_%s(%s *t) {\n", qualifiedClassNameIdentifier.constData(), cdef->qualified.constData());
-        for (const QByteArray &nonClassSignal : std::as_const(cdef->nonClassSignalList))
-            fprintf(out, "    t->%s();\n", nonClassSignal.constData());
+        fprintf(out, "namespace CheckNotifySignalValidity_%s {\n", qualifiedClassNameIdentifier.constData());
+        for (const QByteArray &nonClassSignal : std::as_const(cdef->nonClassSignalList)) {
+            const auto propertyIt = std::find_if(cdef->propertyList.constBegin(),
+                                   cdef->propertyList.constEnd(),
+                                   [&nonClassSignal](const PropertyDef &p) {
+                return nonClassSignal == p.notify;
+            });
+            // must find something, otherwise checkProperties wouldn't have inserted an entry into nonClassSignalList
+            Q_ASSERT(propertyIt != cdef->propertyList.constEnd());
+            fprintf(out, "template<typename T> using has_nullary_%s = decltype(std::declval<T>().%s());\n",
+                    nonClassSignal.constData(),
+                    nonClassSignal.constData());
+            const auto &propertyType = propertyIt->type;
+            fprintf(out, "template<typename T> using has_unary_%s = decltype(std::declval<T>().%s(std::declval<%s>()));\n",
+                    nonClassSignal.constData(),
+                    nonClassSignal.constData(),
+                    propertyType.constData());
+            fprintf(out, "static_assert(qxp::is_detected_v<has_nullary_%s, %s> || qxp::is_detected_v<has_unary_%s, %s>,\n"
+                         "              \"NOTIFY signal %s does not exist in class (or is private in its parent)\");\n",
+                    nonClassSignal.constData(), cdef->qualified.constData(),
+                    nonClassSignal.constData(), cdef->qualified.constData(),
+                    nonClassSignal.constData());
+        }
         fprintf(out, "}\n");
     }
 }
diff --git a/src/tools/moc/moc.cpp b/src/tools/moc/moc.cpp
index e100ff4ba8..b471418a27 100644
--- a/src/tools/moc/moc.cpp
+++ b/src/tools/moc/moc.cpp
@@ -1167,6 +1167,7 @@ void Moc::generate(FILE *out, FILE *jsonOutput)
     fprintf(out, "\n#include <QtCore/qtmochelpers.h>\n");
 
     fprintf(out, "\n#include <memory>\n\n");  // For std::addressof
+    fprintf(out, "\n#include <QtCore/qxptype_traits.h>\n"); // is_detected
 
     fprintf(out, "#if !defined(Q_MOC_OUTPUT_REVISION)\n"
             "#error \"The header file '%s' doesn't include <QObject>.\"\n", fn.constData());
diff --git a/tests/auto/corelib/kernel/qmetaproperty/tst_qmetaproperty.cpp b/tests/auto/corelib/kernel/qmetaproperty/tst_qmetaproperty.cpp
index f459068bef..64f946f430 100644
--- a/tests/auto/corelib/kernel/qmetaproperty/tst_qmetaproperty.cpp
+++ b/tests/auto/corelib/kernel/qmetaproperty/tst_qmetaproperty.cpp
@@ -22,7 +22,14 @@ struct CustomType
 
 Q_DECLARE_METATYPE(CustomType)
 
-class tst_QMetaProperty : public QObject
+class Base : public QObject
+{
+    Q_OBJECT
+signals:
+    void baseSignal(int);
+};
+
+class tst_QMetaProperty : public Base
 {
     Q_OBJECT
     Q_PROPERTY(EnumType value WRITE setValue READ getValue)
@@ -33,6 +40,7 @@ class tst_QMetaProperty : public QObject
     Q_PROPERTY(int value10 READ value10 FINAL)
     Q_PROPERTY(QMap<int, int> map MEMBER map)
     Q_PROPERTY(CustomType custom MEMBER custom)
+    Q_PROPERTY(int propWithInheritedSig READ propWithInheritedSig NOTIFY baseSignal)
 
 private slots:
     void hasStdCppSet();
@@ -43,6 +51,7 @@ private slots:
     void mapProperty();
     void conversion();
     void enumsFlags();
+    void notifySignalIndex();
 
 public:
     enum EnumType { EnumType1 };
@@ -57,6 +66,8 @@ public:
     int value9() const { return 1; }
     int value10() const { return 1; }
 
+    int propWithInheritedSig() const { return 0; }
+
     QString value7;
     QMap<int, int> map;
     CustomType custom;
@@ -274,5 +285,20 @@ void tst_QMetaProperty::enumsFlags()
     QCOMPARE(t.flagProperty(), EnumFlagsTester::flag2);
 }
 
+
+void tst_QMetaProperty::notifySignalIndex()
+{
+    auto mo = this->metaObject();
+    auto propIndex = mo->indexOfProperty("propWithInheritedSig");
+    auto propWithInheritedSig = mo->property(propIndex);
+    QVERIFY(propWithInheritedSig.isValid());
+    QVERIFY(propWithInheritedSig.hasNotifySignal());
+    QVERIFY(propWithInheritedSig.notifySignalIndex() != -1);
+    QMetaMethod notifySignal = propWithInheritedSig.notifySignal();
+    QVERIFY(notifySignal.isValid());
+    QCOMPARE(notifySignal.name(), "baseSignal");
+    QCOMPARE(notifySignal.parameterCount(), 1);
+}
+
 QTEST_MAIN(tst_QMetaProperty)
 #include "tst_qmetaproperty.moc"
diff --git a/tests/auto/tools/moc/tst_moc.cpp b/tests/auto/tools/moc/tst_moc.cpp
index 3a72e9bf4b..1726d09678 100644
--- a/tests/auto/tools/moc/tst_moc.cpp
+++ b/tests/auto/tools/moc/tst_moc.cpp
@@ -257,6 +257,24 @@ public:
 
 CreatableGadget creatableGadget; // Force the compiler to use the constructor
 
+struct ParentWithSignalWithArgument : QObject {
+    Q_OBJECT
+    Q_PROPERTY(int i READ i WRITE setI NOTIFY iChanged)
+
+public:
+    int i() const {return 0;}
+    void setI(int) {}
+
+signals:
+    void iChanged(int);
+};
+
+struct SignalWithArgumentInParent : ParentWithSignalWithArgument
+{
+    Q_OBJECT
+    Q_PROPERTY(int otherI READ i WRITE setI NOTIFY iChanged)
+};
+
 struct MyStruct {};
 struct MyStruct2 {};