API tweak

Author: nyalldawson

python/core/auto_generated/processing/models/qgsprocessingmodelalgorithm.sip.in

@@ -56,6 +56,8 @@ Constructor for QgsProcessingModelAlgorithm.
 
     virtual QString asPythonCommand( const QVariantMap &parameters, QgsProcessingContext &context ) const;
 
+    virtual QgsExpressionContext createExpressionContext( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeatureSource *source = 0 ) const;
+
 
     void setName( const QString &name );
 %Docstring

python/core/auto_generated/processing/qgsprocessingalgorithm.sip.in

@@ -367,7 +367,7 @@ The base class implementation returns None, which indicates that an autogenerate
 parameters widget should be used.
 %End
 
-    QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
+    virtual QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
         QgsProcessingContext &context, QgsProcessingFeatureSource *source = 0 ) const;
 %Docstring
 Creates an expression context relating to the algorithm. This can be called by algorithms

src/core/processing/qgsprocessingalgorithm.h

@@ -376,7 +376,7 @@ class CORE_EXPORT QgsProcessingAlgorithm
      * Optionally, a \a source can be specified which will be used to populate the context if it
      * implements the QgsExpressionContextGenerator interface.
      */
-    QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
+    virtual QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
         QgsProcessingContext &context, QgsProcessingFeatureSource *source = nullptr ) const;
 
     /**