swh.lister.cran: Add description in task_dict

Add description in task_dict method because
the only metadata that can be found for a
package at CRAN is  its decsription.  That can
only br achived from the build in API in R,
which ister is already using. Hence instead of
getting metadata in loader, it is passed
by lister.

swh/lister/cran/lister.py

@@ -5,6 +5,7 @@ import subprocess
 import json
 import logging
 import pkg_resources
+from collections import defaultdict
 
 from swh.lister.cran.models import CRANModel
 
@@ -17,6 +18,7 @@ class CRANLister(SimpleLister):
     MODEL = CRANModel
     LISTER_NAME = 'cran'
     instance = 'cran'
+    descriptions = defaultdict(dict)
 
     def task_dict(self, origin_type, origin_url, **kwargs):
         """Return task format dict
@@ -26,7 +28,8 @@ class CRANLister(SimpleLister):
         """
         return create_task_dict(
             'load-%s' % origin_type, 'recurring',
-            kwargs.get('name'), origin_url, kwargs.get('version'))
+            kwargs.get('name'), origin_url, kwargs.get('version'),
+            project_metadata=self.descriptions[kwargs.get('name')])
 
     def r_script_request(self):
         """Runs R script which uses inbuilt API to return a json
@@ -65,6 +68,7 @@ class CRANLister(SimpleLister):
         """Transform from repository representation to model
 
         """
+        self.descriptions[repo["Package"]] = repo['Description']
         project_url = 'https://cran.r-project.org/src/contrib' \
                       '/%(Package)s_%(Version)s.tar.gz' % repo
         return {

swh/lister/cran/tests/test_lister.py

@@ -0,0 +1,13 @@
+from unittest.mock import patch
+from swh.lister.cran.lister import CRANLister
+
+
+def test_task_dict():
+    lister = CRANLister()
+    lister.descriptions['test_pack'] = 'Test Description'
+    with patch('swh.lister.cran.lister.create_task_dict') as mock_create_tasks:
+        lister.task_dict(origin_type='cran', origin_url='https://abc',
+                         name='test_pack')
+    mock_create_tasks.assert_called_once_with(
+        'load-cran', 'recurring', 'test_pack', 'https://abc', None,
+        project_metadata='Test Description')