Fix valid graph asserting for some dedents that are errors

parso/python/diff.py

@@ -33,10 +33,11 @@ def _assert_valid_graph(node):
 
         # Ignore INDENT is necessary, because indent/dedent tokens don't
         # contain value/prefix and are just around, because of the tokenizer.
-        if node.type == 'error_leaf' and node.token_type in ('INDENT', 'ERROR_DEDENT'):
+        error_tokens = 'INDENT', 'ERROR_DEDENT', 'DEDENT'
+        if node.type == 'error_leaf' and node.token_type in error_tokens:
             return
         while previous_leaf and previous_leaf.type == 'error_leaf' \
-                and previous_leaf.token_type in ('INDENT', 'ERROR_DEDENT'):
+                and previous_leaf.token_type in error_tokens:
             assert previous_leaf.end_pos <= node.start_pos, \
                 (previous_leaf, node)
             previous_leaf = previous_leaf.get_previous_leaf()

test/test_diff_parser.py

@@ -884,3 +884,38 @@ Some'random text: yeah
     differ.initialize(code1)
     differ.parse(code2, parsers=1, copies=1, expect_error_leaves=True)
     differ.parse(code1, parsers=1, copies=1)
+
+
+def test_l(differ):
+    code1 = dedent('''\
+        class C:
+            def f(self):
+                def iterate():
+                    if 1:
+                        yield t
+                    else:
+                        yield
+                return
+
+        def g():
+            3
+        ''')
+
+    code2 = dedent('''\
+            def f(self):
+                def iterate():
+                    if 1:
+                        yield t
+        hahahaha
+                        if 2:
+                            else:
+                                yield
+                return
+
+        def g():
+            3
+        ''')
+
+    differ.initialize(code1)
+    differ.parse(code2, parsers=2, copies=1, expect_error_leaves=True)
+    differ.parse(code1, parsers=1, copies=1)