From 48890134040f9a607c99da9bb15ab39cb30a3f63 Mon Sep 17 00:00:00 2001
From: PJCampi <pierrejean.campigotto@gmail.com>
Date: Wed, 10 Apr 2019 02:33:55 +0200
Subject: [PATCH] get_namespace_name now preserves leading underscore on
 relative import

---
 lark/load_grammar.py                                        | 2 ++
 tests/grammars/leading_underscore_grammar.lark              | 6 ++++++
 tests/test_parser.py                                        | 5 +++++
 .../test_relative_import_preserves_leading_underscore.lark  | 3 +++
 4 files changed, 16 insertions(+)
 create mode 100644 tests/grammars/leading_underscore_grammar.lark
 create mode 100644 tests/test_relative_import_preserves_leading_underscore.lark

diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index b638a71..3608fcb 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -597,6 +597,8 @@ def import_from_grammar_into_namespace(grammar, namespace, aliases):
         try:
             return aliases[name].value
         except KeyError:
+            if name[0] == '_':
+                return '_%s__%s' % (namespace, name[1:])
             return '%s__%s' % (namespace, name)
 
     to_import = list(bfs(aliases, rule_dependencies))
diff --git a/tests/grammars/leading_underscore_grammar.lark b/tests/grammars/leading_underscore_grammar.lark
new file mode 100644
index 0000000..b09a2f4
--- /dev/null
+++ b/tests/grammars/leading_underscore_grammar.lark
@@ -0,0 +1,6 @@
+A: "A"
+
+_SEP: "x"
+_a: A
+
+c: _a _SEP
\ No newline at end of file
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 7cd7dd8..92f2f06 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -1099,6 +1099,11 @@ def _make_parser_test(LEXER, PARSER):
             x = l.parse('12 capybaras')
             self.assertEqual(x.children, ['12', 'capybaras'])
 
+        def test_relative_import_preserves_leading_underscore(self):
+            l = _Lark_open("test_relative_import_preserves_leading_underscore.lark", rel_to=__file__)
+            x = l.parse('Ax')
+            self.assertEqual(next(x.find_data('c')).children, ['A'])
+
         def test_import_errors(self):
             grammar = """
             start: NUMBER WORD
diff --git a/tests/test_relative_import_preserves_leading_underscore.lark b/tests/test_relative_import_preserves_leading_underscore.lark
new file mode 100644
index 0000000..92c08c6
--- /dev/null
+++ b/tests/test_relative_import_preserves_leading_underscore.lark
@@ -0,0 +1,3 @@
+start: c
+
+%import .grammars.leading_underscore_grammar.c
\ No newline at end of file