Fix merge when parent is a dict and child is a list

examples/merge/parent-dict.fmf

@@ -1,9 +1,12 @@
 discover:
     how: fmf
+    summary: test.
 
 /path:
     discover+:
       - name: upstream
         url: https://some.url
+        summary+: upstream
       - name: downstream
         url: https://other.url
+        summary+: downstream

examples/merge/parent-list.fmf

@@ -1,15 +1,19 @@
 discover:
   - how: fmf
     url: https://github.com/project1
+    summary: project1.
   - how: fmf
     url: https://github.com/project2
+    summary: project2.
 
 /tier1:
     summary: basic tests
     discover+:
         filter: "tier: 1"
+        summary+: tier1
 
 /tier2:
     summary: detailed tests
     discover+:
         filter: "tier: 2"
+        summary+: tier2

fmf/base.py

@@ -178,7 +178,8 @@ def _merge_plus(self, data, key, value, prepend=False):
             data[key] = value
             return
 
-        # Special handling for merging lists with dictionary
+        # Parent is a list of dict and child is a dict
+        # (just update every parent list item using the special merge)
         if isinstance(data[key], list) and isinstance(value, dict):
             for list_item in data[key]:
                 if not isinstance(list_item, dict):
@@ -187,20 +188,27 @@ def _merge_plus(self, data, key, value, prepend=False):
                             list_item, self.name))
                 self._merge_special(list_item, value)
             return
+
+        # Parent is a dict and child is a list of dict
+        # (replace parent dict with the list of its special-merged copies)
         if isinstance(data[key], dict) and isinstance(value, list):
+            result_list = []
             for list_item in value:
                 if not isinstance(list_item, dict):
                     raise utils.MergeError(
                         "MergeError: Item '{0}' in {1} must be a dictionary.".format(
                             list_item, self.name))
-                self._merge_special(list_item, data[key])
-            data[key] = value
+                result_dict = copy.deepcopy(data[key])
+                self._merge_special(result_dict, list_item)
+                result_list.append(result_dict)
+            data[key] = result_list
             return
 
         # Use the special merge for merging dictionaries
         if type(data[key]) == type(value) == dict:
             self._merge_special(data[key], value)
             return
+
         # Attempt to apply the plus operator
         try:
             if prepend:

tests/unit/test_base.py

@@ -160,22 +160,32 @@ def test_merge_plus(self):
         with pytest.raises(utils.MergeError):
             child.data["time+"] = "string"
             child.inherit()
+
+    def test_merge_plus_parent_dict(self):
+        """ Merging parent dict with child list """
         child = self.merge.find('/parent-dict/path')
         assert len(child.data['discover']) == 2
         assert child.data['discover'][0]['how'] == 'fmf'
         assert child.data['discover'][0]['name'] == 'upstream'
         assert child.data['discover'][0]['url'] == 'https://some.url'
+        assert child.data['discover'][0]['summary'] == 'test.upstream'
         assert child.data['discover'][1]['how'] == 'fmf'
         assert child.data['discover'][1]['name'] == 'downstream'
         assert child.data['discover'][1]['url'] == 'https://other.url'
+        assert child.data['discover'][1]['summary'] == 'test.downstream'
+
+    def test_merge_plus_parent_list(self):
+        """ Merging parent list with child dict """
         for i in [1, 2]:
             child = self.merge.find(f'/parent-list/tier{i}')
             assert child.data['summary'] == 'basic tests' if i == 1 else 'detailed tests'
             assert len(child.data['discover']) == 2
             assert child.data['discover'][0]['filter'] == f'tier: {i}'
             assert child.data['discover'][0]['url'] == 'https://github.com/project1'
+            assert child.data['discover'][0]['summary'] == f'project1.tier{i}'
             assert child.data['discover'][1]['filter'] == f'tier: {i}'
             assert child.data['discover'][1]['url'] == 'https://github.com/project2'
+            assert child.data['discover'][1]['summary'] == f'project2.tier{i}'
 
     def test_merge_minus(self):
         """ Reducing attributes using the '-' suffix """