Open heart surgery on expression context for processing sources

Author: m-kuhn

python/core/core_auto.sip

@@ -41,6 +41,7 @@
 %Include qgserror.sip
 %Include qgsexpressioncontext.sip
 %Include qgsexpressioncontextgenerator.sip
+%Include qgsexpressioncontextscopegenerator.sip
 %Include qgsexpressionfieldbuffer.sip
 %Include qgsfeaturefilterprovider.sip
 %Include qgsfeatureiterator.sip

python/core/processing/qgsprocessingutils.sip

@@ -274,11 +274,10 @@ class QgsProcessingFeatureSource : QgsFeatureSource
     virtual QVariant maximumValue( int fieldIndex ) const;
 
 
-    QgsExpressionContext createExpressionContext( const QgsProcessingContext &context ) const;
+    QgsExpressionContextScope *createExpressionContextScope() const /Factory/;
 %Docstring
- Returns an expression context scope suitable for this source or a default global/project
- context if nothing more specific can be created.
- :rtype: QgsExpressionContext
+ Returns an expression context scope suitable for this source.
+ :rtype: QgsExpressionContextScope
 %End
 
 };

python/core/qgsexpressioncontextscopegenerator.sip

@@ -0,0 +1,42 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsexpressioncontextscopegenerator.h                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+class QgsExpressionContextScopeGenerator
+{
+%Docstring
+ Abstract interface for generating an expression context scope.
+
+.. versionadded:: 3.0
+%End
+
+%TypeHeaderCode
+#include "qgsexpressioncontextscopegenerator.h"
+%End
+  public:
+
+    virtual QgsExpressionContextScope *createExpressionContextScope() const = 0 /Factory/;
+%Docstring
+ This method needs to be reimplemented in all classes which implement this interface
+ and return an expression context scope.
+
+.. versionadded:: 3.0
+ :rtype: QgsExpressionContextScope
+%End
+
+    virtual ~QgsExpressionContextScopeGenerator();
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsexpressioncontextscopegenerator.h                        *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/core/qgsvectorlayer.sip

@@ -17,7 +17,7 @@ typedef QList<int> QgsAttributeList;
 typedef QSet<int> QgsAttributeIds;
 
 
-class QgsVectorLayer : QgsMapLayer, QgsExpressionContextGenerator, QgsFeatureSink, QgsFeatureSource
+class QgsVectorLayer : QgsMapLayer, QgsExpressionContextGenerator, QgsExpressionContextScopeGenerator, QgsFeatureSink, QgsFeatureSource
 {
 %Docstring
  Represents a vector layer which manages a vector based data sets.
@@ -1783,6 +1783,9 @@ Returns the current blending mode for features
     virtual QgsExpressionContext createExpressionContext() const;
 
 
+    virtual QgsExpressionContextScope *createExpressionContextScope() const /Factory/;
+
+
     QgsEditFormConfig editFormConfig() const;
 %Docstring
  Get the configuration of the form used to represent this vector layer.

src/core/CMakeLists.txt

@@ -855,6 +855,7 @@ SET(QGIS_CORE_HDRS
   qgsexception.h
   qgsexpressioncontext.h
   qgsexpressioncontextgenerator.h
+  qgsexpressioncontextscopegenerator.h
   qgsexpressionfieldbuffer.h
   qgsfeaturefilterprovider.h
   qgsfeatureiterator.h

src/core/processing/qgsprocessingalgorithm.cpp

@@ -132,8 +132,8 @@ QgsExpressionContext QgsProcessingAlgorithm::createExpressionContext( const QVar
   // If there's a source capable of generating a context scope, use it
   if ( source )
   {
-    const auto &scopes = source->createExpressionContext( context ).takeScopes();
-    for ( QgsExpressionContextScope *scope : scopes )
+    QgsExpressionContextScope *scope = source->createExpressionContextScope();
+    if ( scope )
       c << scope;
   }
   else if ( c.scopeCount() == 0 )

src/core/processing/qgsprocessingutils.cpp

@@ -26,6 +26,7 @@
 #include "qgsprocessingparameters.h"
 #include "qgsprocessingalgorithm.h"
 #include "qgsvectorlayerfeatureiterator.h"
+#include "qgsexpressioncontextscopegenerator.h"
 
 QList<QgsRasterLayer *> QgsProcessingUtils::compatibleRasterLayers( QgsProject *project, bool sort )
 {
@@ -721,19 +722,13 @@ QVariant QgsProcessingFeatureSource::maximumValue( int fieldIndex ) const
   return mSource->maximumValue( fieldIndex );
 }
 
-QgsExpressionContext QgsProcessingFeatureSource::createExpressionContext( const QgsProcessingContext &context ) const
+QgsExpressionContextScope *QgsProcessingFeatureSource::createExpressionContextScope() const
 {
-  QgsExpressionContext expressionContext;
-  QgsExpressionContextGenerator *generator = dynamic_cast<QgsExpressionContextGenerator *>( mSource );
+  QgsExpressionContextScope *expressionContextScope = nullptr;
+  QgsExpressionContextScopeGenerator *generator = dynamic_cast<QgsExpressionContextScopeGenerator *>( mSource );
   if ( generator )
   {
-    expressionContext = generator->createExpressionContext();
+    expressionContextScope = generator->createExpressionContextScope();
   }
-  else
-  {
-    expressionContext
-        << QgsExpressionContextUtils::globalScope()
-        << QgsExpressionContextUtils::projectScope( context.project() );
-  }
-  return expressionContext;
+  return expressionContextScope;
 }

src/core/processing/qgsprocessingutils.h

@@ -320,10 +320,9 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
     QVariant maximumValue( int fieldIndex ) const override;
 
     /**
-     * Returns an expression context scope suitable for this source or a default global/project
-     * context if nothing more specific can be created.
+     * Returns an expression context scope suitable for this source.
      */
-    QgsExpressionContext createExpressionContext( const QgsProcessingContext &context ) const;
+    QgsExpressionContextScope *createExpressionContextScope() const SIP_FACTORY;
 
   private:
 

src/core/qgsexpressioncontextscopegenerator.h

@@ -0,0 +1,43 @@
+/***************************************************************************
+  qgsexpressioncontextscopegenerator.h - QgsExpressionContextScopeGenerator
+
+ ---------------------
+ begin                : 24.11.2017
+ copyright            : (C) 2017 by Matthias Kuhn
+ email                : matthias@opengis.ch
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#ifndef QGSEXPRESSIONCONTEXTSCOPEGENERATOR_H
+#define QGSEXPRESSIONCONTEXTSCOPEGENERATOR_H
+
+#include "qgsexpressioncontext.h"
+
+/**
+ * \ingroup core
+ * Abstract interface for generating an expression context scope.
+ *
+ * \since QGIS 3.0
+ */
+
+class CORE_EXPORT QgsExpressionContextScopeGenerator
+{
+  public:
+
+    /**
+     * This method needs to be reimplemented in all classes which implement this interface
+     * and return an expression context scope.
+     *
+     * \since QGIS 3.0
+     */
+    virtual QgsExpressionContextScope *createExpressionContextScope() const = 0 SIP_FACTORY;
+
+    virtual ~QgsExpressionContextScopeGenerator() = default;
+};
+
+#endif // QGSEXPRESSIONCONTEXTGENERATOR_H

src/core/qgsvectorlayer.cpp

@@ -3975,6 +3975,11 @@ QgsExpressionContext QgsVectorLayer::createExpressionContext() const
   return QgsExpressionContext( QgsExpressionContextUtils::globalProjectLayerScopes( this ) );
 }
 
+QgsExpressionContextScope *QgsVectorLayer::createExpressionContextScope() const
+{
+  return QgsExpressionContextUtils::layerScope( this );
+}
+
 void QgsVectorLayer::setDiagramLayerSettings( const QgsDiagramLayerSettings &s )
 {
   if ( !mDiagramLayerSettings )

src/core/qgsvectorlayer.h

@@ -40,6 +40,7 @@
 #include "qgsaggregatecalculator.h"
 #include "qgsfeatureiterator.h"
 #include "qgsexpressioncontextgenerator.h"
+#include "qgsexpressioncontextscopegenerator.h"
 
 class QPainter;
 class QImage;
@@ -350,7 +351,7 @@ typedef QSet<int> QgsAttributeIds;
  * TODO QGIS3: Remove virtual from non-inherited methods (like isModified)
  * \see QgsVectorLayerUtils()
  */
-class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionContextGenerator, public QgsFeatureSink, public QgsFeatureSource
+class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionContextGenerator, public QgsExpressionContextScopeGenerator, public QgsFeatureSink, public QgsFeatureSource
 {
     Q_OBJECT
 
@@ -1741,6 +1742,8 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
 
     QgsExpressionContext createExpressionContext() const override;
 
+    QgsExpressionContextScope *createExpressionContextScope() const override SIP_FACTORY;
+
     /**
      * Get the configuration of the form used to represent this vector layer.
      * This is a writable configuration that can directly be changed in place.