Add QgsAttributes::operator== that takes care of NULL variants

Fixes an issue that the postgres provider would return multiple subsequent
features whose attributes only differ only in 0 vs. NULL.

python/core/qgsfeature.sip

@@ -1,15 +1,13 @@
 
 typedef qint64 QgsFeatureId;
-
-// key = field index, value = field value
 typedef QMap<int, QVariant> QgsAttributeMap;
-
 typedef QVector<QVariant> QgsAttributes;
+
 // QgsAttributes is implemented as a Python list of Python objects.
 %MappedType QgsAttributes /DocType="list-of-attributes"/
 {
 %TypeHeaderCode
-#include <qvector.h>
+#include <qgsfeature.h>
 %End
 
 %ConvertFromTypeCode
@@ -53,7 +51,7 @@ typedef QVector<QVariant> QgsAttributes;
       return 1;
     }
 
-    QVector<QVariant> *qv = new QVector<QVariant>;
+    QgsAttributes* qv = new QgsAttributes;
 
     for (SIP_SSIZE_T i = 0; i < PyList_GET_SIZE(sipPy); ++i)
     {

src/core/qgsfeature.h

@@ -97,7 +97,50 @@ typedef int QgsFeatureId;
 // key = field index, value = field value
 typedef QMap<int, QVariant> QgsAttributeMap;
 
-typedef QVector<QVariant> QgsAttributes;
+/**
+ * A vector of attributes. Mostly equal to QVector<QVariant>.
+ */
+class CORE_EXPORT QgsAttributes : public QVector<QVariant>
+{
+  public:
+    QgsAttributes()
+        : QVector<QVariant>()
+    {}
+    QgsAttributes( int size )
+        : QVector<QVariant>( size )
+    {}
+    QgsAttributes( int size, const QVariant& v )
+        : QVector<QVariant>( size, v )
+    {}
+
+    QgsAttributes( const QVector<QVariant>& v )
+        : QVector<QVariant>( v )
+    {}
+
+    /**
+     * @brief Compares two vectors of attributes.
+     * They are considered equal if all their members contain the same value and NULL flag.
+     * This was introduced because the default Qt implementation of QVariant comparison does not
+     * handle NULL values for certain types (like int).
+     *
+     * @param v The attributes to compare
+     * @return True if v is equal
+     */
+    bool operator==( const QgsAttributes &v ) const
+    {
+      if ( size() != v.size() )
+        return false;
+      const QVariant* b = constData();
+      const QVariant* i = b + size();
+      const QVariant* j = v.constData() + size();
+      while ( i != b )
+        if ( !( *--i == *--j && i->isNull() == j->isNull() ) )
+          return false;
+      return true;
+    }
+
+    inline bool operator!=( const QgsAttributes &v ) const { return !( *this == v ); }
+};
 
 class QgsField;
 

tests/src/python/test_qgsfeature.py

@@ -70,7 +70,6 @@ def test_Attributes(self):
 
         assert myAttributes == myExpectedAttributes, myMessage
 
-    @expectedFailure
     def test_SetAttribute(self):
         feat = QgsFeature()
         feat.initAttributes(1)