gh-152631: Fix ast.parse on lazy imports with older feature_version (#152632)

Author: sobolevn

Grammar/python.gram

@@ -218,15 +218,25 @@ import_stmt[stmt_ty](memo):
 # -----------------
 
 import_name[stmt_ty]:
-    | lazy="lazy"? 'import' a=dotted_as_names { _PyAST_Import(a, lazy ? 1 : 0, EXTRA) }
+    | "lazy" 'import' a=dotted_as_names {
+        CHECK_VERSION(stmt_ty, 15, "Lazy imports are",
+            _PyAST_Import(a, 1, EXTRA)) }
+    | 'import' a=dotted_as_names { _PyAST_Import(a, 0, EXTRA) }
 
 # note below: the ('.' | '...') is necessary because '...' is tokenized as ELLIPSIS
 import_from[stmt_ty]:
     | invalid_import_from
-    | lazy="lazy"? 'from' a=('.' | '...')* b=dotted_name 'import' c=import_from_targets {
-        _PyPegen_checked_from_import(p, a, b, c, lazy, EXTRA) }
-    | lazy="lazy"? 'from' a=('.' | '...')+ 'import' b=import_from_targets {
-        _PyAST_ImportFrom(NULL, b, _PyPegen_seq_count_dots(a), lazy ? 1 : 0, EXTRA) }
+    | lazy="lazy" 'from' a=('.' | '...')* b=dotted_name 'import' c=import_from_targets {
+        CHECK_VERSION(stmt_ty, 15, "Lazy imports are",
+            _PyPegen_checked_from_import(p, a, b, c, lazy, EXTRA)) }
+    | "lazy" 'from' a=('.' | '...')+ 'import' b=import_from_targets {
+        CHECK_VERSION(stmt_ty, 15, "Lazy imports are",
+            _PyAST_ImportFrom(NULL, b, _PyPegen_seq_count_dots(a), 1, EXTRA)) }
+    | 'from' a=('.' | '...')* b=dotted_name 'import' c=import_from_targets {
+        _PyPegen_checked_from_import(p, a, b, c, NULL, EXTRA) }
+    | 'from' a=('.' | '...')+ 'import' b=import_from_targets {
+        _PyAST_ImportFrom(NULL, b, _PyPegen_seq_count_dots(a), 0, EXTRA) }
+
 import_from_targets[asdl_alias_seq*]:
     | '(' a=import_from_as_names [','] ')' { a }
     | import_from_as_names !','

Lib/test/test_ast/test_ast.py

@@ -1031,6 +1031,19 @@ def test_type_params_default_feature_version(self):
                 with self.assertRaises(SyntaxError):
                     ast.parse(sample, feature_version=(3, 12))
 
+    def test_lazy_imports_feature_version(self):
+        samples = [
+            "lazy import os",
+            "lazy from .. import name",
+            "lazy from mod import some",
+        ]
+        for sample in samples:
+            with self.subTest(sample):
+                ast.parse(sample)
+                ast.parse(sample, feature_version=(3, 15))
+                with self.assertRaises(SyntaxError):
+                    ast.parse(sample, feature_version=(3, 14))
+
     def test_invalid_major_feature_version(self):
         with self.assertRaises(ValueError):
             ast.parse('pass', feature_version=(2, 7))

Misc/NEWS.d/next/Core_and_Builtins/2026-06-29-23-01-07.gh-issue-152631.LKgCM_.rst

@@ -0,0 +1,2 @@
+Fix :func:`ast.parse` ability to parse lazy imports with *feature_version*
+older than 3.15, now it properly raises :exc:`SyntaxError`.