QML: Special case null as binding type

This gives us the opportunity to map the JavaScript null to QVariant's
concept of isNull().

[ChangeLog][QML] Assigning JavaScript null to incompatibly typed
properties generates a compile error now, rather than a runtime error.

Fixes: QTBUG-72098
Change-Id: I72fd1c30d84128c774230eaaea10455b2a0e064c
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

13 files changed, 52 insertions, 4 deletions

diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index 84fd66b114..be5e0480b8 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -1083,6 +1083,9 @@ void IRBuilder::setBindingValue(QV4::CompiledData::Binding *binding, QQmlJS::AST
                 binding->type = QV4::CompiledData::Binding::Type_Number;
                 binding->value.constantValueIndex = jsGenerator->registerConstant(QV4::Encode(-lit->value));
             }
+        } else if (QQmlJS::AST::cast<QQmlJS::AST::NullExpression *>(expr)) {
+            binding->type = QV4::CompiledData::Binding::Type_Null;
+            binding->value.nullMarker = 0;
         }
     }
 
diff --git a/src/qml/compiler/qqmlpropertyvalidator.cpp b/src/qml/compiler/qqmlpropertyvalidator.cpp
index 4cb922ca8d..3b97e364e1 100644
--- a/src/qml/compiler/qqmlpropertyvalidator.cpp
+++ b/src/qml/compiler/qqmlpropertyvalidator.cpp
@@ -575,6 +575,9 @@ QQmlCompileError QQmlPropertyValidator::validateLiteralBinding(QQmlPropertyCache
             break;
         } else if (property->propType() == qMetaTypeId<QQmlScriptString>()) {
             break;
+        } else if (property->isQObject()
+                   && binding->type == QV4::CompiledData::Binding::Type_Null) {
+            break;
         }
 
         // otherwise, try a custom type assignment
diff --git a/src/qml/compiler/qv4compileddata.cpp b/src/qml/compiler/qv4compileddata.cpp
index e68a563a45..9379160a65 100644
--- a/src/qml/compiler/qv4compileddata.cpp
+++ b/src/qml/compiler/qv4compileddata.cpp
@@ -745,6 +745,8 @@ QString Binding::valueAsString(const CompilationUnit *unit) const
     case Type_Script:
     case Type_String:
         return unit->stringAt(stringIndex);
+    case Type_Null:
+        return QStringLiteral("null");
     case Type_Boolean:
         return value.b ? QStringLiteral("true") : QStringLiteral("false");
     case Type_Number:
diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index 7c26b0b67d..5732855cc9 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -440,6 +440,7 @@ struct Q_QML_PRIVATE_EXPORT Binding
         Type_Boolean,
         Type_Number,
         Type_String,
+        Type_Null,
         Type_Translation,
         Type_TranslationById,
         Type_Script,
@@ -471,6 +472,7 @@ struct Q_QML_PRIVATE_EXPORT Binding
         quint32_le compiledScriptIndex; // used when Type_Script
         quint32_le objectIndex;
         quint32_le translationDataIndex; // used when Type_Translation
+        quint32 nullMarker;
     } value;
     quint32_le stringIndex; // Set for Type_String and Type_Script (the latter because of script strings)
 
diff --git a/src/qml/qml/qqmlobjectcreator.cpp b/src/qml/qml/qqmlobjectcreator.cpp
index 68e2c2c928..d015a2c0e8 100644
--- a/src/qml/qml/qqmlobjectcreator.cpp
+++ b/src/qml/qml/qqmlobjectcreator.cpp
@@ -381,6 +381,16 @@ void QQmlObjectCreator::setPropertyValue(const QQmlPropertyData *property, const
         }
     }
 
+    if (property->isQObject()) {
+        if (binding->type == QV4::CompiledData::Binding::Type_Null) {
+            QObject *value = nullptr;
+            const bool ok = property->writeProperty(_qobject, &value, propertyWriteFlags);
+            Q_ASSERT(ok);
+            Q_UNUSED(ok);
+            return;
+        }
+    }
+
     switch (propertyType) {
     case QMetaType::QVariant: {
         if (binding->type == QV4::CompiledData::Binding::Type_Number) {
@@ -408,6 +418,13 @@ void QQmlObjectCreator::setPropertyValue(const QQmlPropertyData *property, const
                 QVariant value(binding->valueAsBoolean());
                 property->writeProperty(_qobject, &value, propertyWriteFlags);
             }
+        } else if (binding->type == QV4::CompiledData::Binding::Type_Null) {
+            if (property->isVarProperty()) {
+                _vmeMetaObject->setVMEProperty(property->coreIndex(), QV4::Value::nullValue());
+            } else {
+                QVariant nullValue = QVariant::fromValue(nullptr);
+                property->writeProperty(_qobject, &nullValue, propertyWriteFlags);
+            }
         } else {
             QString stringValue = binding->valueAsString(compilationUnit.data());
             if (property->isVarProperty()) {
@@ -663,6 +680,8 @@ void QQmlObjectCreator::setPropertyValue(const QQmlPropertyData *property, const
                     value = QJSValue(int(n));
                 } else
                     value = QJSValue(n);
+            } else if (binding->type == QV4::CompiledData::Binding::Type_Null) {
+                value = QJSValue::NullValue;
             } else {
                 value = QJSValue(binding->valueAsString(compilationUnit.data()));
             }
diff --git a/src/qml/types/qqmllistmodel.cpp b/src/qml/types/qqmllistmodel.cpp
index debf14df97..27171b9bd4 100644
--- a/src/qml/types/qqmllistmodel.cpp
+++ b/src/qml/types/qqmllistmodel.cpp
@@ -2758,6 +2758,8 @@ bool QQmlListModelParser::applyProperty(const QQmlRefPointer<QV4::CompiledData::
             value = binding->valueAsNumber(compilationUnit->constants);
         } else if (binding->type == QV4::CompiledData::Binding::Type_Boolean) {
             value = binding->valueAsBoolean();
+        } else if (binding->type == QV4::CompiledData::Binding::Type_Null) {
+            value = QVariant::fromValue(nullptr);
         } else if (binding->type == QV4::CompiledData::Binding::Type_Script) {
             QString scriptStr = binding->valueAsScriptString(compilationUnit.data());
             if (definesEmptyList(scriptStr)) {
diff --git a/src/quick/util/qquickpropertychanges.cpp b/src/quick/util/qquickpropertychanges.cpp
index 8e2ac32ace..d739c8a017 100644
--- a/src/quick/util/qquickpropertychanges.cpp
+++ b/src/quick/util/qquickpropertychanges.cpp
@@ -336,6 +336,9 @@ void QQuickPropertyChangesPrivate::decodeBinding(const QString &propertyPrefix,
     case QV4::CompiledData::Binding::Type_Boolean:
         var = binding->valueAsBoolean();
         break;
+    case QV4::CompiledData::Binding::Type_Null:
+        var = QVariant::fromValue(nullptr);
+        break;
     default:
         break;
     }
diff --git a/tests/auto/qml/qqmlcomponent/data/createObjectWithScript.qml b/tests/auto/qml/qqmlcomponent/data/createObjectWithScript.qml
index 989b295cb5..c5ebed612c 100644
--- a/tests/auto/qml/qqmlcomponent/data/createObjectWithScript.qml
+++ b/tests/auto/qml/qqmlcomponent/data/createObjectWithScript.qml
@@ -18,7 +18,7 @@ Item{
         id: b
         Item{
             property bool testBool: false
-            property int testInt: null
+            property int testInt: { return null; }
             property QtObject testObject: null
         }
     }
diff --git a/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml b/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml
new file mode 100644
index 0000000000..6666b85ffd
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml
@@ -0,0 +1,7 @@
+import QtQml 2.2
+
+QtObject {
+    property var foo: null
+    property bool signalSeen: false
+    onFooChanged: signalSeen = true
+}
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 085cd5ffd0..e247ed4eff 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -5991,6 +5991,13 @@ void tst_qqmlecmascript::nullObjectInitializer()
         QVERIFY(value.userType() == qMetaTypeId<QObject*>());
         QVERIFY(!value.value<QObject*>());
     }
+
+    {
+        QQmlComponent component(&engine, testFileUrl("qmlVarNullBinding.qml"));
+        QScopedPointer<QObject> obj(component.create());
+        QVERIFY(!obj.isNull());
+        QVERIFY(!obj->property("signalSeen").toBool());
+    }
 }
 
 // Test that bindings don't evaluate once the engine has been destroyed
diff --git a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.1.qml b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.1.qml
index acd5463a3c..ac5622f9fb 100644
--- a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.1.qml
+++ b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.1.qml
@@ -10,7 +10,7 @@ Item {
         }
     }
 
-    property bool expectNull: null
+    property bool expectNull: { return null; }
 
     function setExpectNull(b) {
         success = false;
diff --git a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.2.qml b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.2.qml
index ed0e0d10f0..3c18739c32 100644
--- a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.2.qml
+++ b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.2.qml
@@ -10,7 +10,7 @@ Item {
         }
     }
 
-    property bool expectNull: null
+    property bool expectNull: { return null; }
 
     function setExpectNull(b) {
         success = false;
diff --git a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.3.qml b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.3.qml
index f5e94ba715..e2e560199f 100644
--- a/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.3.qml
+++ b/tests/auto/qml/qqmllanguage/data/objectDeletionNotify.3.qml
@@ -10,7 +10,7 @@ Item {
         }
     }
 
-    property bool expectNull: null
+    property bool expectNull: { return null; }
 
     function setExpectNull(b) {
         success = false;