Show commit errors in transaction mode

python/core/qgsproject.sip

@@ -467,8 +467,15 @@ class QgsProject : QObject
      */
     void variablesChanged();
 
-  public slots:
+    /**
+     * Emitted whenever a new transaction group has been created or a
+     * transaction group has been removed.
+     *
+     * @note Added in QGIS 3.0
+     */
+    void transactionGroupsChanged();
 
+  public slots:
     /**
      * Flag the project as dirty (modified). If this flag is set, the user will
      * be asked to save changes to the project before closing the current project.

src/app/qgisapp.cpp

@@ -2773,6 +2773,8 @@ void QgisApp::setupConnections()
   connect( this, SIGNAL( projectRead() ),
            this, SLOT( fileOpenedOKAfterLaunch() ) );
 
+  connect( QgsProject::instance(), &QgsProject::transactionGroupsChanged, this, &QgisApp::onTransactionGroupsChanged );
+
   // connect preview modes actions
   connect( mActionPreviewModeOff, SIGNAL( triggered() ), this, SLOT( disablePreviewMode() ) );
   connect( mActionPreviewModeGrayscale, SIGNAL( triggered() ), this, SLOT( activateGrayscalePreview() ) );
@@ -11201,6 +11203,14 @@ void QgisApp::keyPressEvent( QKeyEvent * e )
   }
 }
 
+void QgisApp::onTransactionGroupsChanged()
+{
+  Q_FOREACH ( QgsTransactionGroup* tg, QgsProject::instance()->transactionGroups().values() )
+  {
+    connect( tg, SIGNAL( commitError( QString ) ), this, SLOT( displayMessage( QString, QString, QgsMessageBar::MessageLevel ) ), Qt::UniqueConnection );
+  }
+}
+
 void QgisApp::startProfile( const QString& name )
 {
   mProfiler->start( name );

src/app/qgisapp.h

@@ -726,6 +726,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
 #endif
 
   private slots:
+    void onTransactionGroupsChanged();
+
     //! validate a SRS
     void validateCrs( QgsCoordinateReferenceSystem &crs );
 

src/core/qgsproject.cpp

@@ -995,6 +995,8 @@ void QgsProject::onMapLayersAdded( const QList<QgsMapLayer*>& layers )
 {
   QMap<QString, QgsMapLayer*> existingMaps = QgsMapLayerRegistry::instance()->mapLayers();
 
+  bool tgChanged = false;
+
   Q_FOREACH ( QgsMapLayer* layer, layers )
   {
     QgsVectorLayer* vlayer = qobject_cast<QgsVectorLayer*>( layer );
@@ -1013,8 +1015,7 @@ void QgsProject::onMapLayersAdded( const QList<QgsMapLayer*>& layers )
           {
             tg = new QgsTransactionGroup();
             mTransactionGroups.insert( qMakePair( key, connString ), tg );
-
-            connect( tg, SIGNAL( commitError( QString ) ), this, SLOT( displayMapToolMessage( QString ) ) );
+            tgChanged = true;
           }
           tg->addLayer( vlayer );
         }
@@ -1022,6 +1023,9 @@ void QgsProject::onMapLayersAdded( const QList<QgsMapLayer*>& layers )
       vlayer->dataProvider()->setProviderProperty( QgsVectorDataProvider::EvaluateDefaultValues, evaluateDefaultValues() );
     }
 
+    if ( tgChanged )
+      emit transactionGroupsChanged();
+
     connect( layer, SIGNAL( configChanged() ), this, SLOT( setDirty() ) );
 
     // check if we have to update connections for layers with dependencies
@@ -1039,18 +1043,22 @@ void QgsProject::onMapLayersAdded( const QList<QgsMapLayer*>& layers )
 
 void QgsProject::cleanTransactionGroups( bool force )
 {
+  bool changed = false;
   for ( QMap< QPair< QString, QString>, QgsTransactionGroup*>::Iterator tg = mTransactionGroups.begin(); tg != mTransactionGroups.end(); )
   {
     if ( tg.value()->isEmpty() || force )
     {
       delete tg.value();
       tg = mTransactionGroups.erase( tg );
+      changed = true;
     }
     else
     {
       ++tg;
     }
   }
+  if ( changed )
+    emit transactionGroupsChanged();
 }
 
 bool QgsProject::read( QDomNode &layerNode )

src/core/qgsproject.h

@@ -513,9 +513,11 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
     //! emitted when an old project file is read.
     void oldProjectVersionWarning( const QString& );
 
-    //! emitted when a layer from a projects was read
-    // @param i current layer
-    // @param n number of layers
+    /**
+     * Emitted when a layer from a projects was read.
+     * @param i current layer
+     * @param n number of layers
+     */
     void layerLoaded( int i, int n );
 
     void loadingLayer( const QString& );
@@ -536,8 +538,15 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void variablesChanged();
 
-  public slots:
+    /**
+     * Emitted whenever a new transaction group has been created or a
+     * transaction group has been removed.
+     *
+     * @note Added in QGIS 3.0
+     */
+    void transactionGroupsChanged();
 
+  public slots:
     /**
      * Flag the project as dirty (modified). If this flag is set, the user will
      * be asked to save changes to the project before closing the current project.