[processing] Fix evaluation of linked parameters in batch mode

e.g. missing fields after selecting a layer parameter

Author: nyalldawson

python/plugins/processing/gui/BatchPanel.py

@@ -36,13 +36,15 @@
                        QgsApplication,
                        QgsSettings,
                        QgsProcessingParameterDefinition)
-from qgis.gui import QgsProcessingParameterWidgetContext
+from qgis.gui import (QgsProcessingParameterWidgetContext,
+                      QgsProcessingContextGenerator)
 from qgis.utils import iface
 
 from processing.gui.wrappers import WidgetWrapperFactory, WidgetWrapper
 from processing.gui.BatchOutputSelectionPanel import BatchOutputSelectionPanel
 
 from processing.tools import dataobjects
+from processing.tools.dataobjects import createContext
 
 pluginPath = os.path.split(os.path.dirname(__file__))[0]
 
@@ -87,6 +89,19 @@ def __init__(self, parent, alg):
         self.tblParameters.horizontalHeader().setDefaultSectionSize(250)
         self.tblParameters.horizontalHeader().setMinimumSectionSize(150)
 
+        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)
+
         self.initWidgets()
 
     def layerRegistryChanged(self):
@@ -260,6 +275,7 @@ def setCellWrapper(self, row, column, wrapper, context):
                 widget_context.setMapCanvas(iface.mapCanvas())
             wrapper.setWidgetContext(widget_context)
             widget = wrapper.createWrappedWidget(context)
+            wrapper.registerProcessingContextGenerator(self.context_generator)
         else:
             widget = wrapper.widget