Diff parser: Make sure dedent start pos are matching

parso/python/diff.py

@@ -456,7 +456,7 @@ class _NodesTreeNode(object):
                 if add_error_leaf == 'INDENT':
                     pos = children_part[0].start_pos
                 else:
-                    pos = children[-1].end_pos
+                    pos = children_part[0].start_pos[0], 0
                 children.append(PythonErrorLeaf(add_error_leaf, '', pos))
             children += children_part
         self.tree_node.children = children
@@ -547,11 +547,13 @@ class _NodesTree(object):
                     # having the right indentation.
                     break
             elif tree_node.type == 'file_input':
-                if indentation > 0 and indentation != node.get_latest_indentation():
+                latest_indentation = node.get_latest_indentation()
-                    if previous_node is None:
+                if indentation > 0 and indentation != latest_indentation:
+                    if previous_node is None and indentation > latest_indentation:
                         add_error_leaf = 'INDENT'
                     else:
-                        node = previous_node
+                        if previous_node is not None:
+                            node = previous_node
                         add_error_leaf = 'ERROR_DEDENT'
                 break
             previous_node = node

test/test_diff_parser.py

@@ -47,7 +47,7 @@ def _assert_nodes_are_equal(node1, node2):
         assert node1.value == node2.value
         #assert node1.type == node2.type
         assert node1.prefix == node2.prefix
-        #assert node1.start_pos == node2.start_pos
+        assert node1.start_pos == node2.start_pos
         return
     else:
         try: