Add ast.Constant

Issue #26146: Add a new kind of AST node: ast.Constant. It can be used by
external AST optimizers, but the compiler does not emit directly such node.

An optimizer can replace the following AST nodes with ast.Constant:

* ast.NameConstant: None, False, True
* ast.Num: int, float, complex
* ast.Str: str
* ast.Bytes: bytes
* ast.Tuple if items are constants too: tuple
* frozenset

Update code to accept ast.Constant instead of ast.Num and/or ast.Str:

* compiler
* docstrings
* ast.literal_eval()
* Tools/parser/unparse.py

1 files changed, 50 insertions, 0 deletions

diff --git a/Python/ast.c b/Python/ast.c
index a5d8dba..5422e9c 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -132,6 +132,50 @@ validate_arguments(arguments_ty args)
 }
 
 static int
+validate_constant(PyObject *value)
+{
+    if (value == Py_None || value == Py_Ellipsis)
+        return 1;
+
+    if (PyLong_CheckExact(value)
+            || PyFloat_CheckExact(value)
+            || PyComplex_CheckExact(value)
+            || PyBool_Check(value)
+            || PyUnicode_CheckExact(value)
+            || PyBytes_CheckExact(value))
+        return 1;
+
+    if (PyTuple_CheckExact(value) || PyFrozenSet_CheckExact(value)) {
+        PyObject *it;
+
+        it = PyObject_GetIter(value);
+        if (it == NULL)
+            return 0;
+
+        while (1) {
+            PyObject *item = PyIter_Next(it);
+            if (item == NULL) {
+                if (PyErr_Occurred()) {
+                    Py_DECREF(it);
+                    return 0;
+                }
+                break;
+            }
+
+            if (!validate_constant(item)) {
+                Py_DECREF(it);
+                return 0;
+            }
+        }
+
+        Py_DECREF(it);
+        return 1;
+    }
+
+    return 0;
+}
+
+static int
 validate_expr(expr_ty exp, expr_context_ty ctx)
 {
     int check_ctx = 1;
@@ -240,6 +284,12 @@ validate_expr(expr_ty exp, expr_context_ty ctx)
         return validate_expr(exp->v.Call.func, Load) &&
             validate_exprs(exp->v.Call.args, Load, 0) &&
             validate_keywords(exp->v.Call.keywords);
+    case Constant_kind:
+        if (!validate_constant(exp->v.Constant.value)) {
+            PyErr_SetString(PyExc_TypeError, "invalid type in Constant");
+            return 0;
+        }
+        return 1;
     case Num_kind: {
         PyObject *n = exp->v.Num.n;
         if (!PyLong_CheckExact(n) && !PyFloat_CheckExact(n) &&