Fix diff parser: Invalid dedents meant that sometimes the wrong parents were chosen, fixes davidhalter/jedi#1499

parso/python/diff.py

@@ -281,10 +281,19 @@ class DiffParser(object):
             else:
                 p_children = line_stmt.parent.children
                 index = p_children.index(line_stmt)
+                p_children = p_children[index:]
+                # There might be a random dedent where we have to stop copying.
+                # Invalid indents are ok, because the parser handled that
+                # properly before. An invalid dedent can happen, because a few
+                # lines above there was an invalid indent.
+                indentation = line_stmt.start_pos[1]
+                for i, c in enumerate(p_children):
+                    if c.start_pos[1] < indentation:
+                        p_children = p_children[:i]
 
                 from_ = self._nodes_tree.parsed_until_line + 1
                 copied_nodes = self._nodes_tree.copy_nodes(
-                    p_children[index:],
+                    p_children,
                     until_line_old,
                     line_offset
                 )

test/test_diff_parser.py

@@ -845,8 +845,8 @@ def test_indentation_issues(differ):
 
     differ.initialize(code1)
     differ.parse(code2, parsers=2, copies=2, expect_error_leaves=True)
-    differ.parse(code1, copies=2)
+    differ.parse(code1, copies=2, parsers=1)
-    differ.parse(code3, parsers=2, copies=1)
+    differ.parse(code3, parsers=1, copies=1)
     differ.parse(code1, parsers=1, copies=2)
 
 
@@ -1305,3 +1305,29 @@ def test_async_copy(differ):
     differ.initialize(code1)
     differ.parse(code2, copies=1, parsers=1)
     differ.parse(code1, copies=1, parsers=1, expect_error_leaves=True)
+
+
+def test_parent_on_decorator(differ):
+    code1 = dedent('''\
+        class AClass:
+            @decorator()
+                def b_test(self):
+                print("Hello")
+                print("world")
+
+            def a_test(self):
+                pass''')
+    code2 = dedent('''\
+        class AClass:
+            @decorator()
+            def b_test(self):
+                print("Hello")
+                print("world")
+
+            def a_test(self):
+                pass''')
+    differ.initialize(code1)
+    module_node = differ.parse(code2, copies=2, parsers=1)
+    cls = module_node.children[0]
+    cls_suite = cls.children[-1]
+    assert len(cls_suite.children) == 3