From 820e185dca576f6255fd37d00032a0d7fbf0edd3 Mon Sep 17 00:00:00 2001
From: Chanic Panic <chanicpanic@gmail.com>
Date: Thu, 12 Nov 2020 19:47:53 -0800
Subject: [PATCH 1/2] Fix IndexError (issue #754)

---
 lark/parsers/earley_forest.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/lark/parsers/earley_forest.py b/lark/parsers/earley_forest.py
index 1a71379..03c4573 100644
--- a/lark/parsers/earley_forest.py
+++ b/lark/parsers/earley_forest.py
@@ -459,15 +459,20 @@ class PackedData():
     that comes from the left child and the right child.
     """
 
+    class _NoData():
+        pass
+
+    NO_DATA = _NoData()
+
     def __init__(self, node, data):
-        self.left = None
-        self.right = None
+        self.left = self.NO_DATA
+        self.right = self.NO_DATA
         if data:
-            if node.left:
+            if node.left is not None:
                 self.left = data[0]
-                if len(data) > 1 and node.right:
+                if len(data) > 1:
                     self.right = data[1]
-            elif node.right:
+            else:
                 self.right = data[0]
 
 class ForestToParseTree(ForestTransformer):
@@ -558,12 +563,12 @@ class ForestToParseTree(ForestTransformer):
         children = []
         assert len(data) <= 2
         data = PackedData(node, data)
-        if data.left is not None:
+        if data.left is not PackedData.NO_DATA:
             if node.left.is_intermediate and isinstance(data.left, list):
                 children += data.left
             else:
                 children.append(data.left)
-        if data.right is not None:
+        if data.right is not PackedData.NO_DATA:
             children.append(data.right)
         if node.parent.is_intermediate:
             return children

From 13abf7ca3a89c548fd782e08236d65124f4c7ccb Mon Sep 17 00:00:00 2001
From: Chanic Panic <chanicpanic@gmail.com>
Date: Fri, 13 Nov 2020 12:10:19 -0800
Subject: [PATCH 2/2] Add test for custom indenter

---
 tests/test_parser.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tests/test_parser.py b/tests/test_parser.py
index 6d0981f..6fe2946 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -37,6 +37,7 @@ from lark.tree import Tree
 from lark.visitors import Transformer, Transformer_InPlace, v_args
 from lark.grammar import Rule
 from lark.lexer import TerminalDef, Lexer, TraditionalLexer
+from lark.indenter import Indenter
 
 logger.setLevel(logging.INFO)
 
@@ -1876,6 +1877,28 @@ def _make_parser_test(LEXER, PARSER):
             tree = parser.parse(test_file)
             self.assertEqual(tree.children, [Token('B', 'A')])
 
+        @unittest.skipIf(LEXER=='dynamic', "%declare/postlex doesn't work with dynamic")
+        def test_postlex_indenter(self):
+            class CustomIndenter(Indenter):
+                NL_type = 'NEWLINE'
+                OPEN_PAREN_types = []
+                CLOSE_PAREN_types = []
+                INDENT_type = 'INDENT'
+                DEDENT_type = 'DEDENT'
+                tab_len = 8
+
+            grammar = r"""
+            start: "a" NEWLINE INDENT "b" NEWLINE DEDENT
+
+            NEWLINE: ( /\r?\n */  )+
+
+            %ignore " "+
+            %declare INDENT DEDENT
+            """
+
+            parser = _Lark(grammar, postlex=CustomIndenter())
+            parser.parse("a\n    b\n")
+
         def test_import_custom_sources(self):
             custom_loader = FromPackageLoader('tests', ('grammars', ))