gh-133516: Raise ValueError when constants True, False or None are used as an identifier after NFKC normalization

Lib/test/test_ast/test_ast.py

@@ -821,6 +821,12 @@ def test_constant_as_name(self):
             with self.assertRaisesRegex(ValueError, f"identifier field can't represent '{constant}' constant"):
                 compile(expr, "<test>", "eval")
 
+    def test_constant_as_unicode_name(self):
+        for constant in b"Tru\xe1\xb5\x89", b"Fal\xc5\xbfe", b"N\xc2\xbane":
+            with self.assertRaisesRegex(ValueError,
+                "identifier must not be None, True or False after Unicode normalization \\(NKFC\\)"):
+                ast.parse(constant, mode="eval")
+
     def test_precedence_enum(self):
         class _Precedence(enum.IntEnum):
             """Precedence table that originated from python grammar."""

Misc/NEWS.d/next/Core_and_Builtins/2025-05-06-15-01-41.gh-issue-133516.RqWVf2.rst

@@ -0,0 +1,2 @@
+Raise :exc:`ValueError` when constants ``True``, ``False`` or ``None`` are
+used as an identifier after NFKC normalization.

Parser/pegen.c

@@ -549,6 +549,16 @@ _PyPegen_new_identifier(Parser *p, const char *n)
         }
         id = id2;
     }
+    if (_PyUnicode_EqualToASCIIString(id, "None")
+        || _PyUnicode_EqualToASCIIString(id, "True")
+        || _PyUnicode_EqualToASCIIString(id, "False"))
+    {
+        PyErr_SetString(PyExc_ValueError,
+                        "identifier must not be None, True or False "
+                        "after Unicode normalization (NKFC)");
+        Py_DECREF(id);
+        goto error;
+    }
     PyInterpreterState *interp = _PyInterpreterState_GET();
     _PyUnicode_InternImmortal(interp, &id);
     if (_PyArena_AddPyObject(p->arena, id) < 0)