From e6fc3c9b00306e3a8661210fcc93bf50479ee229 Mon Sep 17 00:00:00 2001
From: MegaIng1 <trampchamp@hotmail.de>
Date: Thu, 16 Jul 2020 18:04:26 +0200
Subject: [PATCH] Added possibility for terminals with different flags to be
 joined in python3.6+

---
 lark/load_grammar.py | 11 +++++++----
 tests/test_parser.py | 16 ++++++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index ee0f1c0..f20feb6 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -5,7 +5,7 @@ import sys
 from copy import copy, deepcopy
 from io import open
 
-from .utils import bfs, eval_escaping
+from .utils import bfs, eval_escaping, Py36
 from .lexer import Token, TerminalDef, PatternStr, PatternRE
 
 from .parse_tree_builder import ParseTreeBuilder
@@ -441,9 +441,12 @@ class TerminalTreeToPattern(Transformer):
         assert items
         if len(items) == 1:
             return items[0]
-        if len({i.flags for i in items}) > 1:
-            raise GrammarError("Lark doesn't support joining terminals with conflicting flags!")
-        return PatternRE(''.join(i.to_regexp() for i in items), items[0].flags if items else ())
+        if not Py36:
+            if len({i.flags for i in items}) > 1:
+                raise GrammarError("Lark doesn't support joining terminals with conflicting flags in python <3.6!")
+            return PatternRE(''.join(i.to_regexp() for i in items), items[0].flags if items else ())
+        else:
+            return PatternRE(''.join(i.to_regexp() for i in items), ())
 
     def expansions(self, exps):
         if len(exps) == 1:
diff --git a/tests/test_parser.py b/tests/test_parser.py
index def4eca..762c979 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -7,6 +7,9 @@ import logging
 import os
 import sys
 from copy import copy, deepcopy
+
+from lark.utils import Py36
+
 try:
     from cStringIO import StringIO as cStringIO
 except ImportError:
@@ -1062,6 +1065,19 @@ def _make_parser_test(LEXER, PARSER):
             g = _Lark(g)
             self.assertEqual( g.parse('"hello"').children, ['"hello"'])
             self.assertEqual( g.parse("'hello'").children, ["'hello'"])
+        
+        @unittest.skipIf(not Py36, "Required re syntax only exists in python3.6+")
+        def test_join_regex_flags(self):
+            g = r"""
+                start: A
+                A: B C
+                B: /./s
+                C: /./
+            """
+            g = _Lark(g)
+            self.assertEqual(g.parse("  ").children,["  "])
+            self.assertEqual(g.parse("\n ").children,["\n "])
+            self.assertRaises(UnexpectedCharacters, g.parse, "\n\n")
 
 
         def test_lexer_token_limit(self):