Cache snapping results in feature dialog for subsequent recalculation of

References #37359

python/gui/auto_generated/qgsattributedialog.sip.in

@@ -73,6 +73,14 @@ Intercept window activate/deactivate events to show/hide the highlighted feature
 :param e: The event
 
 :return: The same as the parent QDialog
+%End
+
+    void setExtraContextScope( QgsExpressionContextScope *extraScope /Transfer/ );
+%Docstring
+Sets an additional expression context scope to be used
+for calculations in this form.
+
+.. versionadded:: 3.16
 %End
 
   public slots:

python/gui/auto_generated/qgsattributeform.sip.in

@@ -167,6 +167,14 @@ In this case it will return a combined expression according to the chosen filter
 on all attribute widgets.
 
 .. versionadded:: 3.0
+%End
+
+    void setExtraContextScope( QgsExpressionContextScope *extraScope /Transfer/ );
+%Docstring
+Sets an additional expression context scope to be used
+for calculations in this form.
+
+.. versionadded:: 3.16
 %End
 
   signals:

src/app/qgsfeatureaction.cpp

@@ -65,6 +65,9 @@ QgsAttributeDialog *QgsFeatureAction::newDialog( bool cloneFeature )
 
   QgsAttributeDialog *dialog = new QgsAttributeDialog( mLayer, f, cloneFeature, parentWidget(), true, context );
   dialog->setWindowFlags( dialog->windowFlags() | Qt::Tool );
+  if ( scope )
+    dialog->setExtraContextScope( new QgsExpressionContextScope( *scope ) );
+
 
   dialog->setObjectName( QStringLiteral( "featureactiondlg:%1:%2" ).arg( mLayer->id() ).arg( f->id() ) );
 
@@ -255,6 +258,8 @@ bool QgsFeatureAction::addFeature( const QgsAttributeMap &defaultAttributes, boo
     dialog->setAttribute( Qt::WA_DeleteOnClose );
     dialog->setMode( QgsAttributeEditorContext::AddFeatureMode );
     dialog->setEditCommandMessage( text() );
+    if ( scope )
+      dialog->setExtraContextScope( new QgsExpressionContextScope( *scope ) );
 
     connect( dialog->attributeForm(), &QgsAttributeForm::featureSaved, this, &QgsFeatureAction::onFeatureSaved );
 

src/gui/qgsattributedialog.cpp

@@ -148,3 +148,8 @@ bool QgsAttributeDialog::event( QEvent *e )
 
   return QDialog::event( e );
 }
+
+void QgsAttributeDialog::setExtraContextScope( QgsExpressionContextScope *extraScope )
+{
+  mAttributeForm->setExtraContextScope( extraScope );
+}

src/gui/qgsattributedialog.h

@@ -95,6 +95,14 @@ class GUI_EXPORT QgsAttributeDialog : public QDialog
      */
     bool event( QEvent *e ) override;
 
+    /**
+     * Sets an additional expression context scope to be used
+     * for calculations in this form.
+     *
+     * \since QGIS 3.16
+     */
+    void setExtraContextScope( QgsExpressionContextScope *extraScope SIP_TRANSFER );
+
   public slots:
     void accept() override;
     void reject() override;

src/gui/qgsattributeform.cpp

@@ -516,7 +516,8 @@ bool QgsAttributeForm::updateDefaultValues( const int originIdx )
         if ( mAlreadyUpdatedFields.contains( eww->fieldIdx() ) )
           continue;
 
-        QString value = mLayer->defaultValue( eww->fieldIdx(), updatedFeature ).toString();
+        QgsExpressionContext context = createExpressionContext( updatedFeature );
+        QString value = mLayer->defaultValue( eww->fieldIdx(), updatedFeature, &context ).toString();
         eww->setValue( value );
       }
     }
@@ -832,6 +833,17 @@ QString QgsAttributeForm::createFilterExpression() const
   return filter;
 }
 
+QgsExpressionContext QgsAttributeForm::createExpressionContext( const QgsFeature &feature ) const
+{
+  QgsExpressionContext context;
+  context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
+  context.appendScope( QgsExpressionContextUtils::formScope( feature, mContext.attributeFormModeString() ) );
+  if ( mExtraContextScope )
+    context.appendScope( new QgsExpressionContextScope( *mExtraContextScope.get() ) );
+  context.setFeature( feature );
+  return context;
+}
+
 
 void QgsAttributeForm::onAttributeChanged( const QVariant &value, const QVariantList &additionalFieldValues )
 {
@@ -950,10 +962,7 @@ void QgsAttributeForm::updateConstraints( QgsEditorWidgetWrapper *eww )
     // sync OK button status
     synchronizeEnabledState();
 
-    QgsExpressionContext context;
+    QgsExpressionContext context = createExpressionContext( ft );
-    context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
-    context.appendScope( QgsExpressionContextUtils::formScope( ft, mContext.attributeFormModeString() ) );
-    context.setFeature( ft );
 
     // Recheck visibility for all containers which are controlled by this value
     const QVector<ContainerInformation *> infos = mContainerInformationDependency.value( eww->field().name() );
@@ -966,10 +975,7 @@ void QgsAttributeForm::updateConstraints( QgsEditorWidgetWrapper *eww )
 
 void QgsAttributeForm::updateContainersVisibility()
 {
-  QgsExpressionContext context;
+  QgsExpressionContext context = createExpressionContext( mFeature );
-  context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
-  context.appendScope( QgsExpressionContextUtils::formScope( mFeature, mContext.attributeFormModeString() ) );
-  context.setFeature( mFeature );
 
   const QVector<ContainerInformation *> infos = mContainerVisibilityInformation;
 
@@ -1017,10 +1023,7 @@ void QgsAttributeForm::updateLabels()
     QgsFeature currentFeature;
     if ( currentFormFeature( currentFeature ) )
     {
-      QgsExpressionContext context;
+      QgsExpressionContext context = createExpressionContext( currentFeature );
-      context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
-      context.appendScope( QgsExpressionContextUtils::formScope( currentFeature, mContext.attributeFormModeString() ) );
-      context.setFeature( currentFeature );
 
       for ( auto it = mLabelDataDefinedProperties.constBegin() ; it != mLabelDataDefinedProperties.constEnd(); ++it )
       {
@@ -2380,6 +2383,11 @@ QString QgsAttributeForm::aggregateFilter() const
   return filters.join( QStringLiteral( " AND " ) );
 }
 
+void QgsAttributeForm::setExtraContextScope( QgsExpressionContextScope *extraScope )
+{
+  mExtraContextScope.reset( extraScope );
+}
+
 int QgsAttributeForm::messageTimeout()
 {
   QgsSettings settings;

src/gui/qgsattributeform.h

@@ -183,6 +183,14 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
      */
     QString aggregateFilter() const;
 
+    /**
+     * Sets an additional expression context scope to be used
+     * for calculations in this form.
+     *
+     * \since QGIS 3.16
+     */
+    void setExtraContextScope( QgsExpressionContextScope *extraScope SIP_TRANSFER );
+
   signals:
 
     /**
@@ -387,6 +395,8 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
 
     QString createFilterExpression() const;
 
+    QgsExpressionContext createExpressionContext( const QgsFeature &feature ) const;
+
     //! constraints management
     void updateAllConstraints();
     void updateConstraints( QgsEditorWidgetWrapper *w );
@@ -407,6 +417,7 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     QgsMessageBarItem *mMultiEditMessageBarItem = nullptr;
     QList<QgsWidgetWrapper *> mWidgets;
     QgsAttributeEditorContext mContext;
+    std::unique_ptr<QgsExpressionContextScope> mExtraContextScope;
     QDialogButtonBox *mButtonBox = nullptr;
     QWidget *mSearchButtonBox = nullptr;
     QList<QgsAttributeFormInterface *> mInterfaces;