Don't optimize global lookups if fast QML lookups are disabled

If fast QML lookups are disabled, we generally want to look up by
string. If the name then happens to be a member of the global JavaScript
object, we still don't want to directly access that, as the name could
have been overridden in a deeper context.

Fixes: QTBUG-73750
Change-Id: Id16110969123d91501064ba46bfad4c2a39e4650
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/qml/compiler/qqmlirbuilder_p.h

@@ -622,6 +622,7 @@ struct Q_QML_PRIVATE_EXPORT JSCodeGen : public QV4::Compiler::Codegen
 
 protected:
     void beginFunctionBodyHook() override;
+    bool canAccelerateGlobalLookups() const override { return !_disableAcceleratedLookups; }
     Reference fallbackNameLookup(const QString &name) override;
 
 private:

src/qml/compiler/qv4codegen.cpp

@@ -2404,7 +2404,7 @@ Codegen::Reference Codegen::referenceForName(const QString &name, bool isLhs, co
 
     Reference r = Reference::fromName(this, name);
     r.global = useFastLookups && (resolved.type == Context::ResolvedName::Global);
-    if (!r.global && m_globalNames.contains(name))
+    if (!r.global && canAccelerateGlobalLookups() && m_globalNames.contains(name))
         r.global = true;
     return r;
 }

src/qml/compiler/qv4codegen_p.h

@@ -561,8 +561,10 @@ protected:
 
     Reference referenceForPropertyName(const Codegen::Reference &object, AST::PropertyName *name);
 
-    // Hook provided to implement QML lookup semantics
+    // Hooks provided to implement QML lookup semantics
+    virtual bool canAccelerateGlobalLookups() const { return true; }
     virtual Reference fallbackNameLookup(const QString &name);
+
     virtual void beginFunctionBodyHook() {}
 
     void emitReturn(const Reference &expr);

tests/auto/qml/qqmlconnections/data/override-proxy-type.qml

@@ -0,0 +1,13 @@
+import QtQml 2.12
+import test.proxy 1.0
+
+Proxy {
+    property int testEnum: 0;
+    id: proxy
+    property Connections connections: Connections {
+        target: proxy
+        onSomeSignal: testEnum = Proxy.EnumValue;
+    }
+
+    Component.onCompleted: someSignal()
+}

tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp

@@ -55,6 +55,7 @@ private slots:
     void disabledAtStart();
     void clearImplicitTarget();
     void onWithoutASignal();
+    void noAcceleratedGlobalLookup();
 
 private:
     QQmlEngine engine;
@@ -407,6 +408,30 @@ void tst_qqmlconnections::onWithoutASignal()
     QVERIFY(item == nullptr); // should parse error, and not give us an item (or crash).
 }
 
+class Proxy : public QObject
+{
+    Q_OBJECT
+public:
+    enum MyEnum { EnumValue = 20, AnotherEnumValue };
+    Q_ENUM(MyEnum)
+
+signals:
+    void someSignal();
+};
+
+void tst_qqmlconnections::noAcceleratedGlobalLookup()
+{
+    qRegisterMetaType<Proxy::MyEnum>();
+    qmlRegisterType<Proxy>("test.proxy", 1, 0, "Proxy");
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("override-proxy-type.qml"));
+    QVERIFY(c.isReady());
+    QScopedPointer<QObject> object(c.create());
+    const QVariant val = object->property("testEnum");
+    QCOMPARE(val.type(), QMetaType::Int);
+    QCOMPARE(val.toInt(), int(Proxy::EnumValue));
+}
+
 QTEST_MAIN(tst_qqmlconnections)
 
 #include "tst_qqmlconnections.moc"