QmlJS: Convert more dynamic_casts to value_casts.

And introduce a good error message for the case when someone
forgets the specialization of the value_cast template.

Change-Id: Iec55a839e8f5eef5872b1dab8601f66e0e0c88de
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>

src/libs/qmljs/qmljsinterpreter.cpp

@@ -704,6 +704,11 @@ const ASTPropertyReference *Value::asAstPropertyReference() const
     return 0;
 }
 
+const ASTSignal *Value::asAstSignal() const
+{
+    return 0;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Values
 ////////////////////////////////////////////////////////////////////////////////
@@ -1982,6 +1987,11 @@ ASTSignal::~ASTSignal()
 {
 }
 
+const ASTSignal *ASTSignal::asAstSignal() const
+{
+    return this;
+}
+
 int ASTSignal::argumentCount() const
 {
     int count = 0;

src/libs/qmljs/qmljsinterpreter.h

@@ -80,6 +80,7 @@ class ASTObjectValue;
 class QmlEnumValue;
 class QmlPrototypeReference;
 class ASTPropertyReference;
+class ASTSignal;
 
 typedef QList<const Value *> ValueList;
 
@@ -134,13 +135,19 @@ public:
     virtual const QmlEnumValue *asQmlEnumValue() const;
     virtual const QmlPrototypeReference *asQmlPrototypeReference() const;
     virtual const ASTPropertyReference *asAstPropertyReference() const;
+    virtual const ASTSignal *asAstSignal() const;
 
     virtual void accept(ValueVisitor *) const = 0;
 
     virtual bool getSourceLocation(QString *fileName, int *line, int *column) const;
 };
 
-template <typename _RetTy> const _RetTy *value_cast(const Value *v);
+template <typename _RetTy> const _RetTy *value_cast(const Value *)
+{
+    // Produce a good error message if a specialization is missing.
+    _RetTy::ERROR_MissingValueCastSpecialization();
+    return 0;
+}
 
 template <> Q_INLINE_TEMPLATE const NullValue *value_cast(const Value *v)
 {
@@ -250,6 +257,12 @@ template <> Q_INLINE_TEMPLATE const ASTPropertyReference *value_cast(const Value
     else   return 0;
 }
 
+template <> Q_INLINE_TEMPLATE const ASTSignal *value_cast(const Value *v)
+{
+    if (v) return v->asAstSignal();
+    else   return 0;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Value nodes
 ////////////////////////////////////////////////////////////////////////////////
@@ -821,6 +834,8 @@ public:
     ASTSignal(AST::UiPublicMember *ast, const Document *doc, ValueOwner *valueOwner);
     virtual ~ASTSignal();
 
+    virtual const ASTSignal *asAstSignal() const;
+
     AST::UiPublicMember *ast() const { return _ast; }
     QString slotName() const { return _slotName; }
     const ObjectValue *bodyScope() const { return _bodyScope; }

src/libs/qmljs/qmljsscopebuilder.cpp

@@ -84,11 +84,11 @@ void ScopeBuilder::push(AST::Node *node)
                     break;
             }
             // signals defined in QML
-            if (const ASTSignal *astsig = dynamic_cast<const ASTSignal *>(value)) {
+            if (const ASTSignal *astsig = value_cast<ASTSignal>(value)) {
                 _scopeChain->appendJsScope(astsig->bodyScope());
             }
             // signals defined in C++
-            else if (const CppComponentValue *qmlObject = dynamic_cast<const CppComponentValue *>(owner)) {
+            else if (const CppComponentValue *qmlObject = value_cast<CppComponentValue>(owner)) {
                 if (const ObjectValue *scope = qmlObject->signalScope(name)) {
                     _scopeChain->appendJsScope(scope);
                 }