Cleaner approach -- create expression contexts in modeler parameter

definition dialogs using expression context and processing context
generators

python/gui/auto_generated/processing/qgsprocessingparameterdefinitionwidget.sip.in

@@ -12,7 +12,8 @@
 
 
 
-class QgsProcessingAbstractParameterDefinitionWidget : QWidget
+
+class QgsProcessingAbstractParameterDefinitionWidget : QWidget, QgsExpressionContextGenerator
 {
 %Docstring
 Abstract base class for widgets which allow users to specify the properties of a
@@ -53,6 +54,42 @@ Common properties for parameters, including the ``name``, ``description``, and p
 method. Subclass implementations must use these properties when crafting a parameter definition which
 also respects the additional properties specific to the parameter type handled by the widget subclass.
 %End
+
+    virtual void setWidgetContext( const QgsProcessingParameterWidgetContext &context );
+%Docstring
+Sets the ``context`` in which the Processing definition widget is shown, e.g., the
+parent model algorithm, a linked map canvas, and other relevant information which allows the widget
+to fine-tune its behavior.
+
+Subclasses should take care to call the base class method when reimplementing this method.
+
+.. seealso:: :py:func:`widgetContext`
+
+.. versionadded:: 3.18
+%End
+
+    const QgsProcessingParameterWidgetContext &widgetContext() const;
+%Docstring
+Returns the context in which the Processing definition widget is shown, e.g., the
+parent model algorithm, a linked map canvas, and other relevant information which allows the widget
+to fine-tune its behavior.
+
+.. seealso:: :py:func:`setWidgetContext`
+
+.. versionadded:: 3.18
+%End
+
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+%Docstring
+Registers a Processing context ``generator`` class that will be used to retrieve
+a Processing context for the widget when required.
+
+.. versionadded:: 3.18
+%End
+
+    virtual QgsExpressionContext createExpressionContext() const;
+
+
 };
 
 
@@ -96,6 +133,14 @@ associated with the parameter.
 Returns a new instance of a parameter definition, using the current settings defined in the dialog.
 
 The ``name`` parameter specifies the name for the newly created parameter.
+%End
+
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+%Docstring
+Registers a Processing context ``generator`` class that will be used to retrieve
+a Processing context for the widget when required.
+
+.. versionadded:: 3.18
 %End
 
 };
@@ -181,6 +226,14 @@ Returns the color for the comments for the parameter.
     void switchToCommentTab();
 %Docstring
 Switches the dialog to the comments tab.
+%End
+
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+%Docstring
+Registers a Processing context ``generator`` class that will be used to retrieve
+a Processing context for the widget when required.
+
+.. versionadded:: 3.18
 %End
 
   public slots:

python/gui/auto_generated/qgsexpressionlineedit.sip.in

@@ -127,15 +127,6 @@ an expression context for the widget.
                   create an expression context when required.
 %End
 
-    void setExpressionContext( QgsExpressionContext &context );
-%Docstring
-Set a default expression context. Will be used if no QgsEcpressionContextGenerator or layer is set.
-
-:param context: The QgsExpressionContext to use.
-
-.. versionadded:: 3.18
-%End
-
   signals:
 
     void expressionChanged( const QString &expression );

python/plugins/processing/modeler/ModelerDialog.py

@@ -40,12 +40,13 @@ from qgis.core import (Qgis,
                        QgsProcessing,
                        QgsProject,
                        QgsProcessingModelParameter,
-                       QgsSettings
+                       QgsSettings,
                        )
 from qgis.gui import (QgsProcessingParameterDefinitionDialog,
                       QgsProcessingParameterWidgetContext,
                       QgsModelGraphicsScene,
-                      QgsModelDesignerDialog)
+                      QgsModelDesignerDialog,
+                      QgsProcessingContextGenerator)
 from processing.gui.HelpEditionDialog import HelpEditionDialog
 from processing.gui.AlgorithmDialog import AlgorithmDialog
 from processing.modeler.ModelerParameterDefinitionDialog import ModelerParameterDefinitionDialog
@@ -105,6 +106,19 @@ class ModelerDialog(QgsModelDesignerDialog):
 
         self.view().centerOn(0, 0)
 
+        self.processing_context = createContext()
+
+        class ContextGenerator(QgsProcessingContextGenerator):
+
+            def __init__(self, context):
+                super().__init__()
+                self.processing_context = context
+
+            def processingContext(self):
+                return self.processing_context
+
+        self.context_generator = ContextGenerator(self.processing_context)
+
     def editHelp(self):
         alg = self.model()
         dlg = HelpEditionDialog(alg)
@@ -270,6 +284,7 @@ class ModelerDialog(QgsModelDesignerDialog):
                                                          context=context,
                                                          widgetContext=widget_context,
                                                          algorithm=self.model())
+            dlg.registerProcessingContextGenerator(self.context_generator)
             if dlg.exec_():
                 new_param = dlg.createParameter()
                 self.autogenerate_parameter_name(new_param)

python/plugins/processing/modeler/ModelerGraphicItem.py

@@ -31,7 +31,8 @@ from qgis.gui import (
     QgsProcessingParameterWidgetContext,
     QgsModelParameterGraphicItem,
     QgsModelChildAlgorithmGraphicItem,
-    QgsModelOutputGraphicItem
+    QgsModelOutputGraphicItem,
+    QgsProcessingContextGenerator
 )
 from processing.modeler.ModelerParameterDefinitionDialog import ModelerParameterDefinitionDialog
 from processing.modeler.ModelerParametersDialog import ModelerParametersDialog
@@ -50,6 +51,19 @@ class ModelerInputGraphicItem(QgsModelParameterGraphicItem):
     def __init__(self, element, model):
         super().__init__(element, model, None)
 
+        self.processing_context = createContext()
+
+        class ContextGenerator(QgsProcessingContextGenerator):
+
+            def __init__(self, context):
+                super().__init__()
+                self.processing_context = context
+
+            def processingContext(self):
+                return self.processing_context
+
+        self.context_generator = ContextGenerator(self.processing_context)
+
     def create_widget_context(self):
         """
         Returns a new widget context for use in the model editor
@@ -91,6 +105,8 @@ class ModelerInputGraphicItem(QgsModelParameterGraphicItem):
                                                          algorithm=self.model())
             dlg.setComments(comment)
             dlg.setCommentColor(comment_color)
+            dlg.registerProcessingContextGenerator(self.context_generator)
+
             if edit_comment:
                 dlg.switchToCommentTab()
 

src/gui/processing/qgsprocessingparameterdefinitionwidget.cpp

@@ -34,14 +34,35 @@
 #include <QTextEdit>
 
 QgsProcessingAbstractParameterDefinitionWidget::QgsProcessingAbstractParameterDefinitionWidget( QgsProcessingContext &,
-    const QgsProcessingParameterWidgetContext &,
+    const QgsProcessingParameterWidgetContext &context,
     const QgsProcessingParameterDefinition *,
     const QgsProcessingAlgorithm *, QWidget *parent )
   : QWidget( parent )
+  , mWidgetContext( context )
 {
 
 }
 
+void QgsProcessingAbstractParameterDefinitionWidget::setWidgetContext( const QgsProcessingParameterWidgetContext &context )
+{
+  mWidgetContext = context;
+}
+
+const QgsProcessingParameterWidgetContext &QgsProcessingAbstractParameterDefinitionWidget::widgetContext() const
+{
+  return mWidgetContext;
+}
+
+void QgsProcessingAbstractParameterDefinitionWidget::registerProcessingContextGenerator( QgsProcessingContextGenerator *generator )
+{
+  mContextGenerator = generator;
+}
+
+QgsExpressionContext QgsProcessingAbstractParameterDefinitionWidget::createExpressionContext() const
+{
+  return QgsProcessingGuiUtils::createExpressionContext( mContextGenerator, mWidgetContext, nullptr, nullptr );
+}
+
 //
 // QgsProcessingParameterDefinitionWidget
 //
@@ -120,6 +141,14 @@ QgsProcessingParameterDefinition *QgsProcessingParameterDefinitionWidget::create
   return param.release();
 }
 
+void QgsProcessingParameterDefinitionWidget::registerProcessingContextGenerator( QgsProcessingContextGenerator *generator )
+{
+  if ( mDefinitionWidget )
+  {
+    mDefinitionWidget->registerProcessingContextGenerator( generator );
+  }
+}
+
 //
 // QgsProcessingParameterDefinitionDialog
 //
@@ -210,6 +239,14 @@ void QgsProcessingParameterDefinitionDialog::switchToCommentTab()
   mCommentEdit->selectAll();
 }
 
+void QgsProcessingParameterDefinitionDialog::registerProcessingContextGenerator( QgsProcessingContextGenerator *generator )
+{
+  if ( mWidget )
+  {
+    mWidget->registerProcessingContextGenerator( generator );
+  }
+}
+
 void QgsProcessingParameterDefinitionDialog::accept()
 {
   if ( mWidget->mDescriptionLineEdit->text().isEmpty() )

src/gui/processing/qgsprocessingparameterdefinitionwidget.h

@@ -25,8 +25,11 @@
 #include "qgis_gui.h"
 #include "qgis_sip.h"
 #include "qgsprocessingparameters.h"
+#include "qgsexpressioncontextgenerator.h"
+#include "qgsprocessingwidgetwrapper.h"
+
+class QgsProcessingContextGenerator;
 
-class QgsProcessingParameterWidgetContext;
 class QLineEdit;
 class QCheckBox;
 class QTabWidget;
@@ -40,7 +43,7 @@ class QgsColorButton;
  * \ingroup gui
  * \since QGIS 3.10
  */
-class GUI_EXPORT QgsProcessingAbstractParameterDefinitionWidget : public QWidget
+class GUI_EXPORT QgsProcessingAbstractParameterDefinitionWidget : public QWidget, public QgsExpressionContextGenerator
 {
     Q_OBJECT
 
@@ -73,6 +76,43 @@ class GUI_EXPORT QgsProcessingAbstractParameterDefinitionWidget : public QWidget
      * also respects the additional properties specific to the parameter type handled by the widget subclass.
      */
     virtual QgsProcessingParameterDefinition *createParameter( const QString &name, const QString &description, QgsProcessingParameterDefinition::Flags flags ) const = 0 SIP_FACTORY;
+
+    /**
+     * Sets the \a context in which the Processing definition widget is shown, e.g., the
+     * parent model algorithm, a linked map canvas, and other relevant information which allows the widget
+     * to fine-tune its behavior.
+     *
+     * Subclasses should take care to call the base class method when reimplementing this method.
+     *
+     * \see widgetContext()
+     * \since QGIS 3.18
+     */
+    virtual void setWidgetContext( const QgsProcessingParameterWidgetContext &context );
+
+    /**
+     * Returns the context in which the Processing definition widget is shown, e.g., the
+     * parent model algorithm, a linked map canvas, and other relevant information which allows the widget
+     * to fine-tune its behavior.
+     *
+     * \see setWidgetContext()
+     * \since QGIS 3.18
+     */
+    const QgsProcessingParameterWidgetContext &widgetContext() const;
+
+    /**
+     * Registers a Processing context \a generator class that will be used to retrieve
+     * a Processing context for the widget when required.
+     *
+     * \since QGIS 3.18
+     */
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+
+    QgsExpressionContext createExpressionContext() const override;
+
+  private:
+
+    QgsProcessingContextGenerator *mContextGenerator = nullptr;
+    QgsProcessingParameterWidgetContext mWidgetContext;
 };
 
 
@@ -117,6 +157,14 @@ class GUI_EXPORT QgsProcessingParameterDefinitionWidget: public QWidget
      */
     QgsProcessingParameterDefinition *createParameter( const QString &name = QString() ) const SIP_FACTORY;
 
+    /**
+     * Registers a Processing context \a generator class that will be used to retrieve
+     * a Processing context for the widget when required.
+     *
+     * \since QGIS 3.18
+     */
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+
   private:
 
     QString mType;
@@ -203,6 +251,14 @@ class GUI_EXPORT QgsProcessingParameterDefinitionDialog: public QDialog
      */
     void switchToCommentTab();
 
+    /**
+     * Registers a Processing context \a generator class that will be used to retrieve
+     * a Processing context for the widget when required.
+     *
+     * \since QGIS 3.18
+     */
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+
   public slots:
     void accept() override;
 

src/gui/processing/qgsprocessingwidgetwrapperimpl.cpp

@@ -1841,18 +1841,13 @@ QgsProcessingAbstractParameterDefinitionWidget *QgsProcessingFileWidgetWrapper::
 QgsProcessingExpressionParameterDefinitionWidget::QgsProcessingExpressionParameterDefinitionWidget( QgsProcessingContext &context, const QgsProcessingParameterWidgetContext &widgetContext, const QgsProcessingParameterDefinition *definition, const QgsProcessingAlgorithm *algorithm, QWidget *parent )
   : QgsProcessingAbstractParameterDefinitionWidget( context, widgetContext, definition, algorithm, parent )
 {
-  mModel = widgetContext.model();
-
   QVBoxLayout *vlayout = new QVBoxLayout();
   vlayout->setContentsMargins( 0, 0, 0, 0 );
   vlayout->addWidget( new QLabel( tr( "Default value" ) ) );
 
   mDefaultLineEdit = new QgsExpressionLineEdit();
-  if ( mModel )
-  {
-    QgsExpressionContext expressionContext = createExpressionContext( context, algorithm );
-    mDefaultLineEdit->setExpressionContext( expressionContext );
-  }
+  mDefaultLineEdit->registerExpressionContextGenerator( this );
+
   if ( const QgsProcessingParameterExpression *expParam = dynamic_cast<const QgsProcessingParameterExpression *>( definition ) )
     mDefaultLineEdit->setExpression( QgsProcessingParameters::parameterAsExpression( expParam, expParam->defaultValueForGui(), context ) );
   vlayout->addWidget( mDefaultLineEdit );
@@ -1866,14 +1861,13 @@ QgsProcessingExpressionParameterDefinitionWidget::QgsProcessingExpressionParamet
   if ( const QgsProcessingParameterExpression *expParam = dynamic_cast<const QgsProcessingParameterExpression *>( definition ) )
     initialParent = expParam->parentLayerParameterName();
 
-
-  if ( mModel )
+  if ( QgsProcessingModelAlgorithm *model = widgetContext.model() )
   {
     // populate combo box with other model input choices
-    const QMap<QString, QgsProcessingModelParameter> components = mModel->parameterComponents();
+    const QMap<QString, QgsProcessingModelParameter> components = model->parameterComponents();
     for ( auto it = components.constBegin(); it != components.constEnd(); ++it )
     {
-      if ( const QgsProcessingParameterFeatureSource *definition = dynamic_cast< const QgsProcessingParameterFeatureSource * >( mModel->parameterDefinition( it.value().parameterName() ) ) )
+      if ( const QgsProcessingParameterFeatureSource *definition = dynamic_cast< const QgsProcessingParameterFeatureSource * >( model->parameterDefinition( it.value().parameterName() ) ) )
       {
         mParentLayerComboBox-> addItem( definition->description(), definition->name() );
         if ( !initialParent.isEmpty() && initialParent == definition->name() )
@@ -1881,7 +1875,7 @@ QgsProcessingExpressionParameterDefinitionWidget::QgsProcessingExpressionParamet
           mParentLayerComboBox->setCurrentIndex( mParentLayerComboBox->count() - 1 );
         }
       }
-      else if ( const QgsProcessingParameterVectorLayer *definition = dynamic_cast< const QgsProcessingParameterVectorLayer * >( mModel->parameterDefinition( it.value().parameterName() ) ) )
+      else if ( const QgsProcessingParameterVectorLayer *definition = dynamic_cast< const QgsProcessingParameterVectorLayer * >( model->parameterDefinition( it.value().parameterName() ) ) )
       {
         mParentLayerComboBox-> addItem( definition->description(), definition->name() );
         if ( !initialParent.isEmpty() && initialParent == definition->name() )
@@ -1907,46 +1901,9 @@ QgsProcessingParameterDefinition *QgsProcessingExpressionParameterDefinitionWidg
 {
   auto param = qgis::make_unique< QgsProcessingParameterExpression >( name, description, mDefaultLineEdit->expression(), mParentLayerComboBox->currentData().toString() );
   param->setFlags( flags );
-  if ( mModel )
-  {
-    QStringList extraVars = mModel->variables().keys();
-    param->setAdditionalExpressionContextVariables( extraVars );
-  }
   return param.release();
 }
 
-QgsExpressionContext QgsProcessingExpressionParameterDefinitionWidget::createExpressionContext( QgsProcessingContext &context, const QgsProcessingAlgorithm *algorithm ) const
-{
-  QgsExpressionContext finalContext = context.expressionContext();
-  QString childId;
-
-  QgsExpressionContextScope *algScope = QgsExpressionContextUtils::processingAlgorithmScope( algorithm, QVariantMap(), context );
-  finalContext.appendScope( algScope );
-
-  QgsExpressionContextScope *modelScope = QgsExpressionContextUtils::processingModelAlgorithmScope( mModel, QVariantMap(), context );
-  finalContext << modelScope;
-  const QgsProcessingAlgorithm *childAlg = nullptr;
-  if ( mModel->childAlgorithms().contains( childId ) )
-    childAlg = mModel->childAlgorithm( childId ).algorithm();
-  QgsExpressionContextScope *algorithmScope = QgsExpressionContextUtils::processingAlgorithmScope( childAlg, QVariantMap(), context );
-  finalContext << algorithmScope;
-
-  QgsExpressionContextScope *childScope = mModel->createExpressionContextScopeForChildAlgorithm( childId, context, QVariantMap(), QVariantMap() );
-  finalContext << childScope;
-
-  QStringList highlightedVariables = childScope->variableNames();
-  QStringList highlightedFunctions = childScope->functionNames();
-  highlightedVariables += algorithmScope->variableNames();
-  highlightedVariables += algScope->variableNames();
-  highlightedVariables += mModel->variables().keys();
-  highlightedFunctions += algScope->functionNames();
-  highlightedFunctions += algorithmScope->functionNames();
-  finalContext.setHighlightedVariables( highlightedVariables );
-  finalContext.setHighlightedFunctions( highlightedFunctions );
-
-  return finalContext;
-}
-
 QgsProcessingExpressionWidgetWrapper::QgsProcessingExpressionWidgetWrapper( const QgsProcessingParameterDefinition *parameter, QgsProcessingGui::WidgetType type, QWidget *parent )
   : QgsAbstractProcessingParameterWidgetWrapper( parameter, type, parent )
 {

src/gui/processing/qgsprocessingwidgetwrapperimpl.h

@@ -66,8 +66,6 @@ class QgsProcessingMapLayerComboBox;
 class QgsRasterBandComboBox;
 class QgsProcessingLayerOutputDestinationWidget;
 class QgsCheckableComboBox;
-class QgsProcessingModelAlgorithm;
-class QgsExpressionContext;
 
 ///@cond PRIVATE
 
@@ -635,13 +633,11 @@ class GUI_EXPORT QgsProcessingExpressionParameterDefinitionWidget : public QgsPr
         const QgsProcessingParameterDefinition *definition = nullptr,
         const QgsProcessingAlgorithm *algorithm = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr );
     QgsProcessingParameterDefinition *createParameter( const QString &name, const QString &description, QgsProcessingParameterDefinition::Flags flags ) const override;
-    QgsExpressionContext createExpressionContext( QgsProcessingContext &context, const QgsProcessingAlgorithm *algorithm ) const;
 
   private:
 
     QComboBox *mParentLayerComboBox = nullptr;
     QgsExpressionLineEdit *mDefaultLineEdit = nullptr;
-    QgsProcessingModelAlgorithm *mModel = nullptr;
 
 };
 

src/gui/qgsexpressionlineedit.h

@@ -132,13 +132,6 @@ class GUI_EXPORT QgsExpressionLineEdit : public QWidget
      */
     void registerExpressionContextGenerator( const QgsExpressionContextGenerator *generator );
 
-    /**
-     * Set a default expression context. Will be used if no QgsEcpressionContextGenerator or layer is set.
-     * \param context The QgsExpressionContext to use.
-     * \since QGIS 3.18
-     */
-    void setExpressionContext( QgsExpressionContext &context ) { mExpressionContext = context; }
-
   signals:
 
     /**