bpo-40847: Consider a line with only a LINECONT a blank line (GH-20769)

A line with only a line continuation character should be considered
a blank line at tokenizer level so that only a single NEWLINE token
gets emitted. The old parser was working around the issue, but the
new parser threw a `SyntaxError` for valid input. For example,
an empty line following a line continuation character was interpreted
as a `SyntaxError`.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/Lib/test/test_peg_parser.py b/Lib/test/test_peg_parser.py
index 6ccb2573176..fae85e323da 100644
--- a/Lib/test/test_peg_parser.py
+++ b/Lib/test/test_peg_parser.py
@@ -153,6 +153,13 @@ TEST_CASES = [
     ('dict_comp', '{x:1 for x in a}'),
     ('dict_comp_if', '{x:1+2 for x in a if b}'),
     ('dict_empty', '{}'),
+    ('empty_line_after_linecont',
+     r'''
+        pass
+        \
+
+        pass
+     '''),
     ('for',
      '''
         for i in a:
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index f41426a4e9d..0c207ec8fc0 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -858,6 +858,20 @@ class SyntaxTestCase(unittest.TestCase):
                           "iterable argument unpacking follows "
                           "keyword argument unpacking")
 
+    def test_empty_line_after_linecont(self):
+        # See issue-40847
+        s = r"""\
+pass
+        \
+
+pass
+"""
+        try:
+            compile(s, '<string>', 'exec')
+        except SyntaxError:
+            self.fail("Empty line after a line continuation character is valid.")
+
+
 def test_main():
     support.run_unittest(SyntaxTestCase)
     from test import test_syntax