Load newest grammar in face of a future grammar

parso/grammar.py

@@ -1,5 +1,6 @@
 import hashlib
 import os
+import warnings
 from typing import Generic, TypeVar, Union, Dict, Optional, Any
 from pathlib import Path
 
@@ -239,7 +240,15 @@ def load_grammar(*, version: str = None, path: str = None):
     :param str version: A python version string, e.g. ``version='3.8'``.
     :param str path: A path to a grammar file
     """
-    version_info = parse_version_string(version)
+    # NOTE: this (3, 14) should be updated to the latest version parso supports.
+    #       (if this doesn't happen, users will get older syntaxes and spurious warnings)
+    passed_version_info = parse_version_string(version)
+    version_info = min(passed_version_info, PythonVersionInfo(3, 14))
+
+    if passed_version_info != version_info:
+        warnings.warn('parso does not support %s.%s yet.' % (
+            passed_version_info.major, passed_version_info.minor
+        ))
 
     file = path or os.path.join(
         'python',

pytest.ini

@@ -10,3 +10,6 @@ norecursedirs = .* docs scripts normalizer_issue_files build
 # fine as long as we are using `clean_jedi_cache` as a session scoped
 # fixture.
 usefixtures = clean_parso_cache
+
+# Disallow warnings
+filterwarnings = error

test/test_load_grammar.py

@@ -4,15 +4,21 @@ from parso import utils
 
 
 def test_load_inexisting_grammar():
-    # This version shouldn't be out for a while, but if we ever do, wow!
+    # We support future grammars assuming future compatibility,
-    with pytest.raises(NotImplementedError):
+    # but we don't know how to parse old grammars.
-        load_grammar(version='15.8')
-    # The same is true for very old grammars (even though this is probably not
-    # going to be an issue.
     with pytest.raises(NotImplementedError):
         load_grammar(version='1.5')
 
 
+def test_load_grammar_uses_older_syntax():
+    with pytest.warns():
+        load_grammar(version='4.0')
+
+
+def test_load_grammar_doesnt_warn(each_version):
+    load_grammar(version=each_version)
+
+
 @pytest.mark.parametrize(('string', 'result'), [
     ('2', (2, 7)), ('3', (3, 6)), ('1.1', (1, 1)), ('1.1.1', (1, 1)), ('300.1.31', (300, 1))
 ])