[processing] Add an example of running a sub-algorithm correctly

to script template file

(cherry-picked from 9ce21e4)

Author: nyalldawson

python/plugins/processing/script/ScriptTemplate.py

@@ -6,6 +6,7 @@
                        QgsProcessingAlgorithm,
                        QgsProcessingParameterFeatureSource,
                        QgsProcessingParameterFeatureSink)
+import processing
 
 
 class ExampleProcessingAlgorithm(QgsProcessingAlgorithm):
@@ -136,6 +137,23 @@ def processAlgorithm(self, parameters, context, feedback):
             # Update the progress bar
             feedback.setProgress(int(current * total))
 
+        # To run another Processing algorithm as part of this algorithm, you can use
+        # processing.run(...). Make sure you pass the current context and feedback
+        # to processing.run to ensure that all temporary layer outputs are available
+        # to the executed algorithm, and that the executed algorithm can send feedback
+        # reports to the user (and correctly handle cancelation and progress reports!)
+        if False:
+            buffered_layer = processing.run("native:buffer", param={
+                'INPUT': dest_id,
+                'DISTANCE': 1.5,
+                'SEGMENTS': 5,
+                'END_CAP_STYLE': 0,
+                'JOIN_STYLE': 0,
+                'MITER_LIMIT': 2,
+                'DISSOLVE': False,
+                'OUTPUT': 'memory:'
+            }, context=context, feedback=feedback)['OUTPUT']
+
         # Return the results of the algorithm. In this case our only result is
         # the feature sink which contains the processed features, but some
         # algorithms may return multiple feature sinks, calculated numeric