Clear existing cache when QgsVectorLayerCache is set to cache geom

Any features inside the cache must be cleared, because they
won't necessarily have the feature's geometry cached

On behalf of Faunalia, sponsored by ENEL

(cherry-picked from 11c444)

Author: nyalldawson

src/core/qgsvectorlayercache.cpp

@@ -58,7 +58,9 @@ int QgsVectorLayerCache::cacheSize()
 
 void QgsVectorLayerCache::setCacheGeometry( bool cacheGeometry )
 {
-  mCacheGeometry = cacheGeometry && mLayer->hasGeometryType();
+  bool shouldCache = cacheGeometry && mLayer->hasGeometryType();
+  bool mustInvalidate = shouldCache && !mCacheGeometry; // going from no geometry -> geometry, so have to clear existing cache entries
+  mCacheGeometry = shouldCache;
   if ( cacheGeometry )
   {
     connect( mLayer, SIGNAL( geometryChanged( QgsFeatureId, QgsGeometry& ) ), SLOT( geometryChanged( QgsFeatureId, QgsGeometry& ) ) );
@@ -67,6 +69,10 @@ void QgsVectorLayerCache::setCacheGeometry( bool cacheGeometry )
   {
     disconnect( mLayer, SIGNAL( geometryChanged( QgsFeatureId, QgsGeometry& ) ), this, SLOT( geometryChanged( QgsFeatureId, QgsGeometry& ) ) );
   }
+  if ( mustInvalidate )
+  {
+    invalidate();
+  }
 }
 
 void QgsVectorLayerCache::setCacheSubsetOfAttributes( const QgsAttributeList& attributes )

tests/src/core/testqgsvectorlayercache.cpp

@@ -54,6 +54,7 @@ class TestVectorLayerCache : public QObject
     void testFullCache();
     void testFullCacheThroughRequest();
     void testCanUseCacheForRequest();
+    void testCacheGeom();
 
     void onCommittedFeaturesAdded( const QString&, const QgsFeatureList& );
 
@@ -330,6 +331,51 @@ void TestVectorLayerCache::testCanUseCacheForRequest()
   QVERIFY( cache.canUseCacheForRequest( QgsFeatureRequest().setFilterExpression( "$x<5" ), it ) );
 }
 
+void TestVectorLayerCache::testCacheGeom()
+{
+  QgsVectorLayerCache cache( mPointsLayer, 2 );
+  // cache geometry
+  cache.setCacheGeometry( true );
+
+  //first get some feature ids from layer
+  QgsFeature f;
+  QgsFeatureIterator it = mPointsLayer->getFeatures();
+  it.nextFeature( f );
+  QgsFeatureId id1 = f.id();
+  it.nextFeature( f );
+  QgsFeatureId id2 = f.id();
+
+  QgsFeatureRequest req;
+  req.setFlags( QgsFeatureRequest::NoGeometry ); // should be ignored by cache
+  req.setFilterFids( QgsFeatureIds() << id1 << id2 );
+
+  it = cache.getFeatures( req );
+  while ( it.nextFeature( f ) )
+  {
+    QVERIFY( f.constGeometry() );
+  }
+
+  // disabled geometry caching
+  cache.setCacheGeometry( false );
+  // we should still have cached features... no need to lose these!
+  QCOMPARE( cache.cachedFeatureIds(), QgsFeatureIds() << id1 << id2 );
+  it = cache.getFeatures( req );
+  while ( it.nextFeature( f ) )
+  {
+    QVERIFY( f.constGeometry() );
+  }
+
+  // now upgrade cache from no geometry -> geometry, should be cleared since we
+  // cannot be confident that features existing in the cache have geometry
+  cache.setCacheGeometry( true );
+  QVERIFY( cache.cachedFeatureIds().isEmpty() );
+  it = cache.getFeatures( req );
+  while ( it.nextFeature( f ) )
+  {
+    QVERIFY( f.constGeometry() );
+  }
+}
+
 void TestVectorLayerCache::onCommittedFeaturesAdded( const QString& layerId, const QgsFeatureList& features )
 {
   Q_UNUSED( layerId )