Ignore ERROR_DEDENT in graph validation

parso/python/diff.py

@@ -31,10 +31,10 @@ 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 == 'INDENT':
+        if node.type == 'error_leaf' and node.token_type in ('INDENT', 'ERROR_DEDENT'):
             return
         while previous_leaf and previous_leaf.type == 'error_leaf' \
-                and previous_leaf.token_type == 'INDENT':
+                and previous_leaf.token_type in ('INDENT', 'ERROR_DEDENT'):
             assert previous_leaf.end_pos <= node.start_pos, \
                 (previous_leaf, node)
             previous_leaf = previous_leaf.get_previous_leaf()

test/test_diff_parser.py

@@ -640,3 +640,28 @@ def test_one_call_in_function_change(differ):
     differ.initialize(code1)
     differ.parse(code2, parsers=1, copies=1, expect_error_leaves=True)
     differ.parse(code1, parsers=2, copies=1)
+
+
+def test_function_deletion(differ):
+    code1 = dedent('''\
+        class C(list):
+            def f(self):
+                def iterate():
+                    for x in b:
+                        break
+
+                return list(iterate())
+        ''')
+
+    code2 = dedent('''\
+        class C():
+            def f(self):
+                    for x in b:
+                        break
+
+                return list(iterate())
+        ''')
+
+    differ.initialize(code1)
+    differ.parse(code2, parsers=1, copies=0, expect_error_leaves=True)
+    differ.parse(code1, parsers=1, copies=0)