gh-140344: ast: Add deprecation warnings

These were all deprecated in 3.9 (bace59d) but without
a runtime deprecation warning. Add it now, so that these
items can be removed in 3.20 per PEP 387.

Author: jepler

Lib/ast.py

@@ -22,7 +22,6 @@
 """
 from _ast import *
 
-
 def parse(source, filename='<unknown>', mode='exec', *,
           type_comments=False, feature_version=None, optimize=-1):
     """
@@ -607,9 +606,13 @@ def __new__(cls, dims=(), **kwargs):
 
     def _dims_getter(self):
         """Deprecated. Use elts instead."""
+        import warnings
+        warnings._deprecated(f"ast.Tuple.dims", remove=(3, 20))
         return self.elts
 
     def _dims_setter(self, value):
+        import warnings
+        warnings._deprecated(f"ast.Tuple.dims", remove=(3, 20))
         self.elts = value
 
     Tuple.dims = property(_dims_getter, _dims_setter)
@@ -689,5 +692,23 @@ def main(args=None):
     print(dump(tree, include_attributes=args.include_attributes,
                indent=args.indent, show_empty=args.show_empty))
 
+_deprecated = {
+        'slice': globals().pop("slice"),
+        'Index': globals().pop("Index"),
+        'ExtSlice': globals().pop("ExtSlice"),
+        'Suite': globals().pop("Suite"),
+        'AugLoad': globals().pop("AugLoad"),
+        'AugStore': globals().pop("AugStore"),
+        'Param': globals().pop("Param")
+}
+
+def __getattr__(attr):
+    if val := _deprecated.get(attr, None):
+        import warnings
+        warnings._deprecated(f"ast.{attr}", remove=(3, 20))
+        globals()[attr] = val
+        return val
+    raise AttributeError(f"module 'ast' has no attribute {attr!r}")
+
 if __name__ == '__main__':
     main()

Lib/test/test_ast/test_ast.py

@@ -502,6 +502,12 @@ def test_classattrs(self):
         self.assertIs(ast.Constant(None).value, None)
         self.assertIs(ast.Constant(...).value, ...)
 
+        with self.assertWarns(DeprecationWarning):
+            ast.Tuple().dims
+
+        with self.assertWarns(DeprecationWarning):
+            ast.Tuple().dims = 3
+
     def test_constant_subclasses(self):
         class N(ast.Constant):
             def __init__(self, *args, **kwargs):
@@ -1124,6 +1130,28 @@ def test_tstring(self):
         self.assertIsInstance(tree.body[0].value.values[0], ast.Constant)
         self.assertIsInstance(tree.body[0].value.values[1], ast.Interpolation)
 
+    def test_deprecated(self):
+        with self.assertWarns(DeprecationWarning):
+            ast.slice
+
+        with self.assertWarns(DeprecationWarning):
+            ast.Index
+
+        with self.assertWarns(DeprecationWarning):
+            ast.ExtSlice
+
+        with self.assertWarns(DeprecationWarning):
+            ast.Suite
+
+        with self.assertWarns(DeprecationWarning):
+            ast.AugLoad
+
+        with self.assertWarns(DeprecationWarning):
+            ast.AugStore
+
+        with self.assertWarns(DeprecationWarning):
+            ast.Param
+
 
 class CopyTests(unittest.TestCase):
     """Test copying and pickling AST nodes."""

Misc/NEWS.d/next/Library/2025-10-20-09-12-18.gh-issue-140344.WjbYg-.rst

@@ -0,0 +1,3 @@
+The classes ``ast.Suite``, ``ast.AugLoad``, ``ast.AugStore``, and
+``ast.Param``, deprecated since Python 3.9, now issue deprecation warnings
+on use. They are now scheduled for removal in Python 3.20.