Fix a diff parser issue.

parso/python/diff.py

@@ -14,7 +14,7 @@ from parso.utils import splitlines
 from parso.python.parser import Parser
 from parso.python.tree import EndMarker
 from parso.python.tokenize import (tokenize_lines, NEWLINE, TokenInfo,
-                                   ENDMARKER, INDENT, DEDENT)
+                                   ENDMARKER, INDENT, DEDENT, ERRORTOKEN)
 
 
 def _get_last_line(node_or_leaf):
@@ -301,7 +301,11 @@ class DiffParser(object):
                     continue
             is_first_token = False
 
-            if typ == DEDENT:
+            # In case of omitted_first_indent, it might not be dedented fully.
+            # However this is a sign for us that a dedent happened.
+            if typ == DEDENT \
+                    or typ == ERRORTOKEN and not string \
+                    and omitted_first_indent and len(indents) == 1:
                 indents.pop()
                 if omitted_first_indent and not indents:
                     # We are done here, only thing that can come now is an

parso/python/tokenize.py

@@ -248,7 +248,6 @@ def tokenize_lines(lines):
                 txt = line[pos:]
                 if txt.endswith('\n'):
                     new_line = True
-                # TODO remove prefix?
                 yield TokenInfo(ERRORTOKEN, txt, (lnum, pos), additional_prefix)
                 additional_prefix = ''
                 break
@@ -279,6 +278,7 @@ def tokenize_lines(lines):
                     while start < indents[-1]:
                         if start > indents[-2]:
                             yield TokenInfo(ERRORTOKEN, '', spos, '')
+                            print(spos, repr(line))
                             break
                         yield TokenInfo(DEDENT, '', spos, '')
                         indents.pop()

test/test_diff_parser.py

@@ -463,6 +463,20 @@ def test_in_parentheses_newlines(differ):
     b = 2""")
 
 
+def test_indentation_issue(differ):
+    code1 = dedent("""
+        import module
+    """)
+
+    code2 = dedent("""
+        class L1:
+            class L2:
+                class L3:
+                    def f(): pass
+                def f(): pass
+            def f(): pass
+        def f(): pass
+    """)
+
     differ.initialize(code1)
-    differ.parse(code2, parsers=2, copies=1)
-    differ.parse(code1, parsers=2, copies=1)
+    differ.parse(code2, parsers=2)