Fix memory provider handling of missing attributes when adding features

Ensure that features added to a memory provider (and returned when
fetching features from a memory provider) always have the correct
number of attributes present.

Fixes many random behavior bugs when working with memory providers.

src/core/providers/memory/qgsmemoryprovider.cpp

@@ -346,11 +346,24 @@ bool QgsMemoryProvider::addFeatures( QgsFeatureList &flist, Flags )
   // whether or not to update the layer extent on the fly as we add features
   bool updateExtent = mFeatures.isEmpty() || !mExtent.isEmpty();
 
+  int fieldCount = mFields.count();
+
   // TODO: sanity checks of fields and geometries
   for ( QgsFeatureList::iterator it = flist.begin(); it != flist.end(); ++it )
   {
     it->setId( mNextFeatureId );
     it->setValid( true );
+    if ( it->attributes().count() < fieldCount )
+    {
+      // ensure features have the correct number of attributes by padding
+      // them with null attributes for missing values
+      QgsAttributes attributes = it->attributes();
+      for ( int i = it->attributes().count(); i < mFields.count(); ++i )
+      {
+        attributes.append( QVariant( mFields.at( i ).type() ) );
+      }
+      it->setAttributes( attributes );
+    }
 
     mFeatures.insert( mNextFeatureId, *it );
 

tests/src/python/providertestbase.py

@@ -463,8 +463,8 @@ def testAddFeatureMissingAttributes(self):
         f2.setId(added[1].id())
 
         # check result - feature attributes MUST be padded out to required number of fields
-        f1.setAttributes([6, -220, NULL, 'String', NULL])
-        f2.setAttributes([7, 330, NULL, NULL, NULL])
+        f1.setAttributes([6, -220, NULL, 'String', 'NULL'])
+        f2.setAttributes([7, 330, NULL, NULL, 'NULL'])
         self.testGetFeatures(l.dataProvider(), [f1, f2])
 
     def testAddFeaturesUpdateExtent(self):