gh-107625: configparser: Raise error if a missing value is continued (GH-107651)

Co-authored-by: Éric <merwok@netwok.org>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Jason R. Coombs <jaraco@jaraco.com>

Lib/test/test_configparser.py

@@ -1555,6 +1555,30 @@ def test_source_as_bytes(self):
             "'[badbad'"
         )
 
+    def test_keys_without_value_with_extra_whitespace(self):
+        lines = [
+            '[SECT]\n',
+            'KEY1\n',
+            ' KEY2 = VAL2\n', # note the Space before the key!
+        ]
+        parser = configparser.ConfigParser(
+            comment_prefixes="",
+            allow_no_value=True,
+            strict=False,
+            delimiters=('=',),
+            interpolation=None,
+        )
+        with self.assertRaises(configparser.MultilineContinuationError) as dse:
+            parser.read_file(lines)
+        self.assertEqual(
+            str(dse.exception),
+            "Key without value continued with an indented line.\n"
+            "file: '<???>', line: 3\n"
+            "' KEY2 = VAL2\\n'"
+        )
+
+
+
 
 class CoverageOneHundredTestCase(unittest.TestCase):
     """Covers edge cases in the codebase."""