Avoid recursion in lex_indent() on long comments. Fix #1280.

Author: Guido van Rossum

mypy/lex.py

@@ -688,15 +688,16 @@ def lex_space(self) -> None:
     def lex_indent(self) -> None:
         """Analyze whitespace chars at the beginning of a line (indents)."""
         s = self.match(self.indent_exp)
-        if s != '' and s[-1] in self.comment_or_newline:
+        while True:
+            s = self.match(self.indent_exp)
+            if s == '' or s[-1] not in self.comment_or_newline:
+                break
             # Empty line (whitespace only or comment only).
             self.add_pre_whitespace(s[:-1])
             if s[-1] == '#':
                 self.lex_comment()
             else:
                 self.lex_break()
-            self.lex_indent()
-            return
         indent = self.calc_indent(s)
         if indent == self.indents[-1]:
             # No change in indent: just whitespace.

mypy/test/testlex.py

@@ -426,6 +426,10 @@ def test_byte_order_mark(self):
         self.assert_lex('\ufeff"\xbb"'.encode('utf8'),
                         'Bom(\ufeff) StrLit("\xbb") Break() Eof()')
 
+    def test_long_comment(self):
+        prog = '# pass\n' * 1000
+        self.assert_lex(prog, 'Eof(%s)' % repr(prog)[1:-1])
+
     # TODO
     #   invalid escape sequences in string literals etc.