[processing] Also expose complete expression context inside

data defined buttons for model child algorithms

The context was not previously exposed, so users would not have
been aware that they can utilise all the variables and functions
available to parameters within child algorithms.

Author: nyalldawson

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

@@ -64,6 +64,12 @@ parent model algorithm and other relevant information which allows the widget
 to fine-tune its behavior.
 
 .. seealso:: :py:func:`widgetContext`
+%End
+
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+%Docstring
+Register a Processing context ``generator`` class that will be used to retrieve
+a Processing context for the widget when required.
 %End
 
     void populateSources( const QStringList &compatibleParameterTypes,

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

@@ -109,7 +109,7 @@ Sets the child algorithm ``id`` within the model which the parameter widget is a
 
 };
 
-class QgsAbstractProcessingParameterWidgetWrapper : QObject
+class QgsAbstractProcessingParameterWidgetWrapper : QObject, QgsExpressionContextGenerator
 {
 %Docstring
 
@@ -232,7 +232,7 @@ Returns the current value of the parameter.
 
     void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
 %Docstring
-Register a Processing context generator class that will be used to retrieve
+Register a Processing context ``generator`` class that will be used to retrieve
 a Processing context for the wrapper when required.
 %End
 
@@ -242,6 +242,9 @@ Called after all wrappers have been created within a particular dialog or contex
 allowing the wrapper to connect to the wrappers of other, related parameters.
 %End
 
+    virtual QgsExpressionContext createExpressionContext() const;
+
+
   signals:
 
 

python/plugins/processing/modeler/ModelerParametersDialog.py

@@ -36,7 +36,6 @@
                                  QHBoxLayout, QWidget)
 
 from qgis.core import (Qgis,
-                       QgsApplication,
                        QgsProcessingParameterDefinition,
                        QgsProcessingParameterPoint,
                        QgsProcessingParameterExtent,
@@ -58,6 +57,7 @@
                       QgsScrollArea,
                       QgsFilterLineEdit,
                       QgsHelp,
+                      QgsProcessingContextGenerator,
                       QgsProcessingModelerParameterWidget,
                       QgsProcessingParameterWidgetContext)
 from qgis.utils import iface
@@ -83,8 +83,20 @@ def __init__(self, alg, model, algName=None, configuration=None):
 
         self.widget_labels = {}
 
+        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.context)
+
         self.setupUi()
         self.params = None
+
         settings = QgsSettings()
         self.restoreGeometry(settings.value("/Processing/modelParametersDialogGeometry", QByteArray()))
 
@@ -135,6 +147,8 @@ def setupUi(self):
 
         widget_context = QgsProcessingParameterWidgetContext()
         widget_context.setMapCanvas(iface.mapCanvas())
+        widget_context.setModel(self.model)
+        widget_context.setModelChildAlgorithmId(self.childId)
 
         for param in self._alg.parameterDefinitions():
             if param.flags() & QgsProcessingParameterDefinition.FlagAdvanced:
@@ -156,6 +170,7 @@ def setupUi(self):
 
             if issubclass(wrapper.__class__, QgsProcessingModelerParameterWidget):
                 wrapper.setWidgetContext(widget_context)
+                wrapper.registerProcessingContextGenerator(self.context_generator)
                 widget = wrapper
             else:
                 widget = wrapper.widget

src/gui/processing/qgsprocessingmodelerparameterwidget.cpp

@@ -121,6 +121,12 @@ void QgsProcessingModelerParameterWidget::setWidgetContext( const QgsProcessingP
     mStaticWidgetWrapper->setWidgetContext( context );
 }
 
+void QgsProcessingModelerParameterWidget::registerProcessingContextGenerator( QgsProcessingContextGenerator *generator )
+{
+  if ( mStaticWidgetWrapper )
+    mStaticWidgetWrapper->registerProcessingContextGenerator( generator );
+}
+
 const QgsProcessingParameterDefinition *QgsProcessingModelerParameterWidget::parameterDefinition() const
 {
   return mParameterDefinition;
@@ -176,7 +182,10 @@ QgsExpressionContext QgsProcessingModelerParameterWidget::createExpressionContex
   QgsExpressionContext c = mContext.expressionContext();
   if ( mModel )
   {
-    QgsExpressionContextScope *algorithmScope = QgsExpressionContextUtils::processingAlgorithmScope( mModel->childAlgorithm( mChildId ).algorithm(), QVariantMap(), mContext );
+    const QgsProcessingAlgorithm *alg = nullptr;
+    if ( mModel->childAlgorithms().contains( mChildId ) )
+      alg = mModel->childAlgorithm( mChildId ).algorithm();
+    QgsExpressionContextScope *algorithmScope = QgsExpressionContextUtils::processingAlgorithmScope( alg, QVariantMap(), mContext );
     c << algorithmScope;
     QgsExpressionContextScope *childScope = mModel->createExpressionContextScopeForChildAlgorithm( mChildId, mContext, QVariantMap(), QVariantMap() );
     c << childScope;
@@ -305,6 +314,9 @@ void QgsProcessingModelerParameterWidget::populateSources( const QStringList &co
 
       case QgsProcessingModelChildParameterSource::ChildOutput:
       {
+        if ( !mModel->childAlgorithms().contains( source.outputChildId() ) )
+          continue;
+
         const QgsProcessingModelChildAlgorithm &alg = mModel->childAlgorithm( source.outputChildId() );
         if ( !alg.algorithm() )
           continue;

src/gui/processing/qgsprocessingmodelerparameterwidget.h

@@ -31,6 +31,7 @@ class QgsAbstractProcessingParameterWidgetWrapper;
 class QgsExpressionLineEdit;
 class QgsProcessingModelAlgorithm;
 class QgsProcessingParameterWidgetContext;
+class QgsProcessingContextGenerator;
 
 class QLabel;
 class QToolButton;
@@ -92,6 +93,12 @@ class GUI_EXPORT QgsProcessingModelerParameterWidget : public QWidget, public Qg
      */
     void setWidgetContext( const QgsProcessingParameterWidgetContext &context );
 
+    /**
+     * Register a Processing context \a generator class that will be used to retrieve
+     * a Processing context for the widget when required.
+     */
+    void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
+
     /**
      * Populates the widget with available sources for the parameter's value, e.g.
      * adding the available child algorithm outputs and model input parameter

src/gui/processing/qgsprocessingwidgetwrapper.cpp

@@ -20,6 +20,8 @@
 #include "qgsprocessingparameters.h"
 #include "qgsprocessingmodelerparameterwidget.h"
 #include "qgspropertyoverridebutton.h"
+#include "qgsexpressioncontext.h"
+#include "models/qgsprocessingmodelalgorithm.h"
 #include <QLabel>
 #include <QHBoxLayout>
 
@@ -101,6 +103,7 @@ QWidget *QgsAbstractProcessingParameterWidgetWrapper::createWrappedWidget( QgsPr
     hLayout->addWidget( mPropertyButton );
     mPropertyButton->init( 0, QgsProperty(), mParameterDefinition->dynamicPropertyDefinition() );
     mPropertyButton->registerEnabledWidget( mWidget, false );
+    mPropertyButton->registerExpressionContextGenerator( this );
 
     wrappedWidget = new QWidget();
     wrappedWidget->setLayout( hLayout );
@@ -211,6 +214,47 @@ void QgsAbstractProcessingParameterWidgetWrapper::postInitialize( const QList<Qg
   }
 }
 
+QgsExpressionContext QgsAbstractProcessingParameterWidgetWrapper::createExpressionContext() const
+{
+  // Get a processing context to start with
+  QgsProcessingContext *context = nullptr;
+  std::unique_ptr< QgsProcessingContext > tmpContext;
+  if ( mProcessingContextGenerator )
+    context = mProcessingContextGenerator->processingContext();
+
+  if ( !context )
+  {
+    tmpContext = qgis::make_unique< QgsProcessingContext >();
+    context = tmpContext.get();
+  }
+
+  QgsExpressionContext c = context->expressionContext();
+
+  if ( mPropertyButton->vectorLayer() )
+    c << QgsExpressionContextUtils::layerScope( mPropertyButton->vectorLayer() );
+
+  if ( mWidgetContext.model() )
+  {
+    const QgsProcessingAlgorithm *alg = nullptr;
+    if ( mWidgetContext.model()->childAlgorithms().contains( mWidgetContext.modelChildAlgorithmId() ) )
+      alg = mWidgetContext.model()->childAlgorithm( mWidgetContext.modelChildAlgorithmId() ).algorithm();
+
+    QgsExpressionContextScope *algorithmScope = QgsExpressionContextUtils::processingAlgorithmScope( alg, QVariantMap(), *context );
+    c << algorithmScope;
+    QgsExpressionContextScope *childScope = mWidgetContext.model()->createExpressionContextScopeForChildAlgorithm( mWidgetContext.modelChildAlgorithmId(), *context, QVariantMap(), QVariantMap() );
+    c << childScope;
+
+    QStringList highlightedVariables = childScope->variableNames();
+    QStringList highlightedFunctions = childScope->functionNames();
+    highlightedVariables += algorithmScope->variableNames();
+    highlightedFunctions += algorithmScope->functionNames();
+    c.setHighlightedVariables( highlightedVariables );
+    c.setHighlightedFunctions( highlightedFunctions );
+  }
+
+  return c;
+}
+
 void QgsAbstractProcessingParameterWidgetWrapper::parentLayerChanged( QgsAbstractProcessingParameterWidgetWrapper *wrapper )
 {
   if ( wrapper )

src/gui/processing/qgsprocessingwidgetwrapper.h

@@ -153,7 +153,7 @@ class GUI_EXPORT QgsProcessingParameterWidgetContext
  * \ingroup gui
  * \since QGIS 3.4
  */
-class GUI_EXPORT QgsAbstractProcessingParameterWidgetWrapper : public QObject
+class GUI_EXPORT QgsAbstractProcessingParameterWidgetWrapper : public QObject, public QgsExpressionContextGenerator
 {
     Q_OBJECT
 
@@ -257,7 +257,7 @@ class GUI_EXPORT QgsAbstractProcessingParameterWidgetWrapper : public QObject
     QVariant parameterValue() const;
 
     /**
-     * Register a Processing context generator class that will be used to retrieve
+     * Register a Processing context \a generator class that will be used to retrieve
      * a Processing context for the wrapper when required.
      */
     void registerProcessingContextGenerator( QgsProcessingContextGenerator *generator );
@@ -268,6 +268,8 @@ class GUI_EXPORT QgsAbstractProcessingParameterWidgetWrapper : public QObject
      */
     virtual void postInitialize( const QList< QgsAbstractProcessingParameterWidgetWrapper * > &wrappers );
 
+    QgsExpressionContext createExpressionContext() const override;
+
   signals:
 
     // TODO QGIS 4.0 - remove wrapper parameter - this is kept for compatibility with 3.x API,