Added sanity check of links between graphicitems showing error in dia…

…log. Fixes #40724 #39260

python/gui/auto_generated/processing/models/qgsmodelgraphicsscene.sip.in

@@ -148,7 +148,7 @@ Sets the message ``bar`` associated with the scene.
 .. seealso:: :py:func:`messageBar`
 %End
 
-    void showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level = Qgis::Warning );
+    void showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level = Qgis::Warning ) const;
 %Docstring
 Shows a warning message, allowing users to click a button to see the full details (``longMessage``).
 %End

python/plugins/processing/modeler/ModelerDialog.py

@@ -221,8 +221,9 @@ def repaintModel(self, showControls=True):
             scene.setFlag(QgsModelGraphicsScene.FlagHideComments)
 
         context = createContext()
-        scene.createItems(self.model(), context)
         self.setModelScene(scene)
+        # create items later that setModelScene to setup link to messageBar to the scene
+        scene.createItems(self.model(), context)
 
     def create_widget_context(self):
         """

src/gui/processing/models/qgsmodelcomponentgraphicitem.cpp

@@ -983,12 +983,21 @@ QString QgsModelChildAlgorithmGraphicItem::linkPointText( Qt::Edge edge, int ind
   if ( const QgsProcessingModelChildAlgorithm *child = dynamic_cast< const QgsProcessingModelChildAlgorithm * >( component() ) )
   {
     if ( !child->algorithm() )
-      return 0;
+      return QString();
 
     switch ( edge )
     {
       case Qt::BottomEdge:
       {
+        if ( index >= child->algorithm()->outputDefinitions().length() )
+        {
+          // something goes wrong and tried to link to an not existing output
+          QgsMessageLog::logMessage(
+            tr( "Cannot link output for child: %1" ).arg( child->algorithm()->name() ),
+            "QgsModelChildAlgorithmGraphicItem", Qgis::Warning, true );
+          return QString();
+        }
+
         const QgsProcessingOutputDefinition *output = child->algorithm()->outputDefinitions().at( index );
         QString title = output->description();
         if ( mResults.contains( output->name() ) )
@@ -1006,6 +1015,14 @@ QString QgsModelChildAlgorithmGraphicItem::linkPointText( Qt::Edge edge, int ind
           return param->flags() & QgsProcessingParameterDefinition::FlagHidden || param->isDestination();
         } ), params.end() );
 
+        if ( index >= params.length() )
+        {
+          // something goes wrong and tried to link to an not existing source parameter
+          QgsMessageLog::logMessage(
+            tr( "Cannot link source for child: %1" ).arg( child->algorithm()->name() ),
+            "QgsModelChildAlgorithmGraphicItem", Qgis::Warning, true );
+          return QString();
+        }
 
         QString title = params.at( index )->description();
         if ( !mInputs.value( params.at( index )->name() ).toString().isEmpty() )

src/gui/processing/models/qgsmodelgraphicsscene.cpp

@@ -22,6 +22,7 @@
 #include "qgsmessagebar.h"
 #include "qgsmessagebaritem.h"
 #include "qgsmessageviewer.h"
+#include "qgsapplication.h"
 #include <QGraphicsSceneMouseEvent>
 #include <QPushButton>
 
@@ -409,6 +410,20 @@ QList<QgsModelGraphicsScene::LinkSource> QgsModelGraphicsScene::linkSourcesForPa
           LinkSource l;
           l.item = mChildAlgorithmItems.value( source.outputChildId() );
           l.edge = Qt::BottomEdge;
+
+          // do sanity check of linked index
+          if ( i >= model->childAlgorithm( source.outputChildId() ).algorithm()->outputDefinitions().length() )
+          {
+            QString short_message = tr( "Check output links for alg: %1" ).arg( model->childAlgorithm( source.outputChildId() ).algorithm()->name() );
+            QString long_message = tr( "Cannot link output for alg: %1" ).arg( model->childAlgorithm( source.outputChildId() ).algorithm()->name() );
+            QString title( tr( "Algorithm link error" ) );
+            if ( messageBar() )
+              showWarning( const_cast<QString &>( short_message ), const_cast<QString &>( title ), const_cast<QString &>( long_message ) );
+            else
+              QgsMessageLog::logMessage( long_message, "QgsModelGraphicsScene", Qgis::Warning, true );
+            break;
+          }
+
           l.linkIndex = i;
           res.append( l );
         }
@@ -467,7 +482,7 @@ void QgsModelGraphicsScene::setMessageBar( QgsMessageBar *messageBar )
   mMessageBar = messageBar;
 }
 
-void QgsModelGraphicsScene::showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level )
+void QgsModelGraphicsScene::showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level ) const
 {
   QgsMessageBarItem *messageWidget = mMessageBar->createMessage( QString(), shortMessage );
   QPushButton *detailsButton = new QPushButton( tr( "Details" ) );
@@ -484,4 +499,3 @@ void QgsModelGraphicsScene::showWarning( const QString &shortMessage, const QStr
 }
 
 ///@endcond
-

src/gui/processing/models/qgsmodelgraphicsscene.h

@@ -164,7 +164,7 @@ class GUI_EXPORT QgsModelGraphicsScene : public QGraphicsScene
     /**
      * Shows a warning message, allowing users to click a button to see the full details (\a longMessage).
      */
-    void showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level = Qgis::Warning );
+    void showWarning( const QString &shortMessage, const QString &title, const QString &longMessage, Qgis::MessageLevel level = Qgis::Warning ) const;
 
   signals: