Fix slow updates from field calculator

Fixes #20094

Followup 096b4ce

Author: elpaso

python/core/auto_generated/qgsvectorlayer.sip.in

@@ -2377,6 +2377,13 @@ Is emitted, before changes are committed to the data provider
     void beforeRollBack();
 %Docstring
 Is emitted, before changes are rolled back
+%End
+
+    void afterRollBack();
+%Docstring
+Is emitted, after changes are rolled back
+
+.. versionadded:: 3.4
 %End
 
     void attributeAdded( int idx );

src/core/qgsvectorlayer.cpp

@@ -2983,6 +2983,8 @@ bool QgsVectorLayer::rollBack( bool deleteBuffer )
 
   mEditBuffer->rollBack();
 
+  emit afterRollBack();
+
   if ( isModified() )
   {
     // new undo stack roll back method

src/core/qgsvectorlayer.h

@@ -2173,6 +2173,12 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
     //! Is emitted, before changes are rolled back
     void beforeRollBack();
 
+    /**
+     * Is emitted, after changes are rolled back
+     * \since QGIS 3.4
+     */
+    void afterRollBack();
+
     /**
      * Will be emitted, when a new attribute has been added to this vector layer.
      * Applies only to types QgsFields::OriginEdit, QgsFields::OriginProvider and QgsFields::OriginExpression

src/gui/attributetable/qgsattributetablemodel.cpp

@@ -62,13 +62,20 @@ QgsAttributeTableModel::QgsAttributeTableModel( QgsVectorLayerCache *layerCache,
 
   loadAttributes();
 
-  connect( mLayerCache, &QgsVectorLayerCache::attributeValueChanged, this, &QgsAttributeTableModel::attributeValueChanged );
   connect( layer(), &QgsVectorLayer::featuresDeleted, this, &QgsAttributeTableModel::featuresDeleted );
   connect( layer(), &QgsVectorLayer::attributeDeleted, this, &QgsAttributeTableModel::attributeDeleted );
   connect( layer(), &QgsVectorLayer::updatedFields, this, &QgsAttributeTableModel::updatedFields );
+
+  connect( layer(), &QgsVectorLayer::editCommandStarted, this, [ = ]( const QString ) { mBulkEditCommandRunning = true; } );
+  connect( layer(), &QgsVectorLayer::editCommandEnded, this, [ = ]   { mBulkEditCommandRunning = false; } );
+  connect( layer(), &QgsVectorLayer::beforeRollBack, this, [ = ] { mBulkEditCommandRunning = true; } );
+  connect( layer(), &QgsVectorLayer::afterRollBack, this, [ = ] { mBulkEditCommandRunning = false; } );
+
   connect( layer(), &QgsVectorLayer::editCommandEnded, this, &QgsAttributeTableModel::editCommandEnded );
+  connect( mLayerCache, &QgsVectorLayerCache::attributeValueChanged, this, &QgsAttributeTableModel::attributeValueChanged );
   connect( mLayerCache, &QgsVectorLayerCache::featureAdded, this, [ = ]( QgsFeatureId id ) { featureAdded( id ); } );
   connect( mLayerCache, &QgsVectorLayerCache::cachedLayerDeleted, this, &QgsAttributeTableModel::layerDeleted );
+
 }
 
 bool QgsAttributeTableModel::loadFeatureAtId( QgsFeatureId fid ) const
@@ -294,6 +301,9 @@ void QgsAttributeTableModel::fieldFormatterRemoved( QgsFieldFormatter *fieldForm
 
 void QgsAttributeTableModel::attributeValueChanged( QgsFeatureId fid, int idx, const QVariant &value )
 {
+  // Skip all updates if an edit command is running
+  if ( mBulkEditCommandRunning )
+    return;
   QgsDebugMsgLevel( QStringLiteral( "(%4) fid: %1, idx: %2, value: %3" ).arg( fid ).arg( idx ).arg( value.toString() ).arg( mFeatureRequest.filterType() ), 3 );
 
   for ( SortCache &cache : mSortCaches )

src/gui/attributetable/qgsattributetablemodel.h

@@ -391,6 +391,9 @@ class GUI_EXPORT QgsAttributeTableModel: public QAbstractTableModel
 
     int mExtraColumns = 0;
 
+    //! Edit command or rollback is running
+    bool mBulkEditCommandRunning = false;
+
     friend class TestQgsAttributeTable;
 
 };