Ensure that cached vector getFeatures request respect provider ordering

src/core/qgscachedfeatureiterator.cpp

@@ -45,15 +45,15 @@ QgsCachedFeatureIterator::QgsCachedFeatureIterator( QgsVectorLayerCache *vlCache
   switch ( featureRequest.filterType() )
   {
     case QgsFeatureRequest::FilterFids:
-      mFeatureIds = featureRequest.filterFids();
+      mFeatureIds = QList< QgsFeatureId >( qgis::setToList( featureRequest.filterFids() ) );
       break;
 
     case QgsFeatureRequest::FilterFid:
-      mFeatureIds = QgsFeatureIds() << featureRequest.filterFid();
+      mFeatureIds = QList< QgsFeatureId >() << featureRequest.filterFid();
       break;
 
     default:
-      mFeatureIds = qgis::listToSet( mVectorLayerCache->mCache.keys() );
+      mFeatureIds = mVectorLayerCache->mCacheOrderedKeys;
       break;
   }
 

src/core/qgscachedfeatureiterator.h

@@ -76,9 +76,9 @@ class CORE_EXPORT QgsCachedFeatureIterator : public QgsAbstractFeatureIterator
     bool nextFeatureFilterFids( QgsFeature &f ) override { return fetchFeature( f ); }
 
   private:
-    QgsFeatureIds mFeatureIds;
+    QList< QgsFeatureId > mFeatureIds;
     QgsVectorLayerCache *mVectorLayerCache = nullptr;
-    QgsFeatureIds::ConstIterator mFeatureIdIterator;
+    QList< QgsFeatureId >::ConstIterator mFeatureIdIterator;
     QgsCoordinateTransform mTransform;
     QgsRectangle mFilterRect;
 };

src/core/qgsvectorlayercache.cpp

@@ -173,7 +173,10 @@ bool QgsVectorLayerCache::featureAtId( QgsFeatureId featureId, QgsFeature &featu
 
 bool QgsVectorLayerCache::removeCachedFeature( QgsFeatureId fid )
 {
-  return mCache.remove( fid );
+  bool removed = mCache.remove( fid );
+  if ( removed )
+    mCacheOrderedKeys.removeOne( fid );
+  return removed;
 }
 
 QgsVectorLayer *QgsVectorLayerCache::layer()
@@ -265,6 +268,7 @@ void QgsVectorLayerCache::onJoinAttributeValueChanged( QgsFeatureId fid, int fie
 void QgsVectorLayerCache::featureDeleted( QgsFeatureId fid )
 {
   mCache.remove( fid );
+  mCacheOrderedKeys.removeOne( fid );
 }
 
 void QgsVectorLayerCache::onFeatureAdded( QgsFeatureId fid )
@@ -323,6 +327,7 @@ void QgsVectorLayerCache::layerDeleted()
 void QgsVectorLayerCache::invalidate()
 {
   mCache.clear();
+  mCacheOrderedKeys.clear();
   mFullCache = false;
   emit invalidated();
 }

src/core/qgsvectorlayercache.h

@@ -393,10 +393,13 @@ class CORE_EXPORT QgsVectorLayerCache : public QObject
     {
       QgsCachedFeature *cachedFeature = new QgsCachedFeature( feat, this );
       mCache.insert( feat.id(), cachedFeature );
+      if ( !mCacheOrderedKeys.contains( feat.id() ) )
+        mCacheOrderedKeys << feat.id();
     }
 
     QgsVectorLayer *mLayer = nullptr;
     QCache< QgsFeatureId, QgsCachedFeature > mCache;
+    QList< QgsFeatureId > mCacheOrderedKeys;
 
     bool mCacheGeometry = true;
     bool mFullCache = false;

tests/src/core/testqgsvectorlayercache.cpp

@@ -267,11 +267,15 @@ void TestVectorLayerCache::testFullCacheThroughRequest()
     // suck in all features
   }
 
-  // cache should now contain all features
+  // cache should now contain all features, and should iterate through in the same order as the non-cached feature ordering
   it = mPointsLayer->getFeatures();
+  QgsFeatureIterator itCached = cache.getFeatures( QgsFeatureRequest() );
+  QgsFeature fCached;
   while ( it.nextFeature( f ) )
   {
     QVERIFY( cache.isFidCached( f.id() ) );
+    itCached.nextFeature( fCached );
+    QCOMPARE( f.id(), fCached.id() );
   }
 
   // so it should be a full cache!