From 9923987e94547ded8a17d7a03840c4cebce39188 Mon Sep 17 00:00:00 2001
From: decorator-factory <42166884+decorator-factory@users.noreply.github.com>
Date: Mon, 10 Aug 2020 23:07:55 +0300
Subject: [PATCH] allow multiline regexes with 'x' (verbose) flag

---
 lark/load_grammar.py | 13 ++++++++++---
 tests/test_parser.py | 26 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index ae7ec32..d716ec1 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -13,7 +13,7 @@ from .parser_frontends import LALR_TraditionalLexer
 from .common import LexerConf, ParserConf
 from .grammar import RuleOptions, Rule, Terminal, NonTerminal, Symbol
 from .utils import classify, suppress, dedup_list, Str
-from .exceptions import GrammarError, UnexpectedCharacters, UnexpectedToken
+from .exceptions import GrammarError, LarkError, UnexpectedCharacters, UnexpectedToken
 
 from .tree import Tree, SlottedTree as ST
 from .visitors import Transformer, Visitor, v_args, Transformer_InPlace, Transformer_NonRecursive
@@ -85,7 +85,7 @@ TERMINALS = {
     'RULE': '!?[_?]?[a-z][_a-z0-9]*',
     'TERMINAL': '_?[A-Z][_A-Z0-9]*',
     'STRING': r'"(\\"|\\\\|[^"\n])*?"i?',
-    'REGEXP': r'/(?!/)(\\/|\\\\|[^/\n])*?/[%s]*' % _RE_FLAGS,
+    'REGEXP': r'/(?!/)(\\/|\\\\|[^/])*?/[%s]*' % _RE_FLAGS,
     '_NL': r'(\r?\n)+\s*',
     'WS': r'[ \t]+',
     'COMMENT': r'\s*//[^\n]*',
@@ -336,7 +336,7 @@ class PrepareAnonTerminals(Transformer_InPlace):
                     term_name = None
 
         elif isinstance(p, PatternRE):
-            if p in self.term_reverse: # Kind of a wierd placement.name
+            if p in self.term_reverse: # Kind of a weird placement.name
                 term_name = self.term_reverse[p].name
         else:
             assert False, p
@@ -409,6 +409,13 @@ def _literal_to_pattern(literal):
     flags = v[flag_start:]
     assert all(f in _RE_FLAGS for f in flags), flags
 
+    if literal.type == 'STRING' and '\n' in v:
+        raise GrammarError('You cannot put newlines in string literals')
+
+    if literal.type == 'REGEXP' and '\n' in v and 'x' not in flags:
+        raise GrammarError('You can only use newlines in regular expressions '
+                           'with the `x` (verbose) flag')
+
     v = v[:flag_start]
     assert v[0] == v[-1] and v[0] in '"/'
     x = v[1:-1]
diff --git a/tests/test_parser.py b/tests/test_parser.py
index cd3ea4d..48a4674 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -1262,6 +1262,32 @@ def _make_parser_test(LEXER, PARSER):
             tree = l.parse('aA')
             self.assertEqual(tree.children, ['a', 'A'])
 
+        def test_token_flags_verbose(self):
+            g = _Lark(r"""start: NL | ABC
+                          ABC: / [a-z] /x
+                          NL: /\n/
+                      """)
+            x = g.parse('a')
+            self.assertEqual(x.children, ['a'])
+
+        def test_token_flags_verbose_multiline(self):
+            g = _Lark(r"""start: ABC
+                          ABC: /  a      b c
+                               d
+                                e f
+                           /x
+                       """)
+            x = g.parse('abcdef')
+            self.assertEqual(x.children, ['abcdef'])
+
+        def test_token_multiline_only_works_with_x_flag(self):
+            g = r"""start: ABC
+                    ABC: /  a      b c
+                              d
+                                e f
+                            /i
+                      """
+            self.assertRaises( GrammarError, _Lark, g)
 
         @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_twice_empty(self):