Add some support to flag alias properties

This is required if we want to be able to get rid of the property
cache.

Also reserve a flag for var properties, in case it turns out that we
need to keep the distinction between var and QVariant properties in QML.

Change-Id: I55c2191adcc2d94bd8f148216e26423defaa900f
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/corelib/kernel/qmetaobject.cpp

@@ -3031,6 +3031,20 @@ bool QMetaProperty::hasStdCppSet() const
     return (data.flags() & StdCppSet);
 }
 
+/*!
+    \internal
+
+    Returns \c true if the property is an alias.
+    This is for instance true for a property declared in QML
+    as 'property alias'.
+*/
+bool QMetaProperty::isAlias() const
+{
+    if (!mobj)
+        return false;
+    return (data.flags() & Alias);
+}
+
 /*!
     \internal
     Executes metacall with QMetaObject::RegisterPropertyMetaType flag.

src/corelib/kernel/qmetaobject.h

@@ -314,6 +314,7 @@ public:
     bool resetOnGadget(void *gadget) const;
 
     bool hasStdCppSet() const;
+    bool isAlias() const;
     inline bool isValid() const { return isReadable(); }
     inline const QMetaObject *enclosingMetaObject() const { return mobj; }
 

src/corelib/kernel/qmetaobject_p.h

@@ -71,6 +71,8 @@ enum PropertyFlags  {
     Writable = 0x00000002,
     Resettable = 0x00000004,
     EnumOrFlag = 0x00000008,
+    Alias = 0x00000010,
+    //Reserved for future usage = 0x00000020,
     StdCppSet = 0x00000100,
     Constant = 0x00000400,
     Final = 0x00000800,

src/corelib/kernel/qmetaobjectbuilder.cpp

@@ -2367,6 +2367,19 @@ bool QMetaPropertyBuilder::isFinal() const
         return false;
 }
 
+/*!
+ * Returns \c true if the property is an alias.
+ * The default value is false
+ */
+bool QMetaPropertyBuilder::isAlias() const
+{
+    QMetaPropertyBuilderPrivate *d = d_func();
+    if (d)
+        return d->flag(Alias);
+    else
+        return false;
+}
+
 /*!
     Sets this property to readable if \a value is true.
 
@@ -2502,6 +2515,16 @@ void QMetaPropertyBuilder::setFinal(bool value)
         d->setFlag(Final, value);
 }
 
+/*!
+   Sets the \c ALIAS flag on this property to \a value
+ */
+void QMetaPropertyBuilder::setAlias(bool value)
+{
+    QMetaPropertyBuilderPrivate *d = d_func();
+    if (d)
+        d->setFlag(Alias, value);
+}
+
 /*!
     Returns the revision of this property.
 

src/corelib/kernel/qmetaobjectbuilder_p.h

@@ -262,6 +262,7 @@ public:
     bool isEnumOrFlag() const;
     bool isConstant() const;
     bool isFinal() const;
+    bool isAlias() const;
 
     void setReadable(bool value);
     void setWritable(bool value);
@@ -274,6 +275,7 @@ public:
     void setEnumOrFlag(bool value);
     void setConstant(bool value);
     void setFinal(bool value);
+    void setAlias(bool value);
 
     int revision() const;
     void setRevision(int revision);